GASCO exit exam questions and answers — Advanced Training for Liquefied Gas Tanker Cargo Operations

All 710 questions from the Advanced Training for Liquefied Gas Tanker Cargo Operations (GASCO) exit exam bank, with the correct option marked and a one-line explanation for every one. Read it end to end, jump to a single set, or search it — then sit the same bank as a timed paper. The real DG Shipping exit exam is 30 marks with 15 to pass.

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Set 1 — 30 GASCO exit exam questions with answers

1. What is the primary component of Liquefied Natural Gas (LNG)?

A. Methane
B. Butane
C. Propane
D. Ethane

Answer: A — Methane

LNG consists predominantly of methane (typically over 85-95%) along with small percentages of ethane, propane, and butane.

2. At atmospheric pressure, what is the approximate boiling point of methane?

A. −42 °C
B. −104 °C
C. 0 °C
D. −162 °C

Answer: D — −162 °C

Methane, the main component of LNG, boils at about −161.5 °C (−162 °C) at atmospheric pressure. −42 °C is propane and −104 °C is ethylene.

3. Which code governs the construction and equipment of ships carrying liquefied gases in bulk?

A. IGC Code
B. IMSBC Code
C. IMDG Code
D. IBC Code

Answer: A — IGC Code

The International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code) is mandatory under SOLAS Chapter VII.

4. What is the function of Boil-Off Gas (BOG) on an LNG carrier?

A. It is dumped directly into seawater
B. It must be vented continuously into the atmosphere
C. It is used to extinguish boiler fires
D. It is generated due to heat ingress and can be used as fuel or re-liquefied

Answer: D — It is generated due to heat ingress and can be used as fuel or re-liquefied

Boil-Off Gas (BOG) forms when cargo absorbs ambient heat. Modern gas carriers use BOG in dual-fuel propulsion engines or re-liquefy it back into the cargo tanks.

5. What gas is used to inert cargo tanks on gas carriers before introducing gas cargo?

A. Dry Nitrogen or Inert Gas with low O2
B. Oxygen
C. Compressed air
D. Carbon Dioxide only

Answer: A — Dry Nitrogen or Inert Gas with low O2

Nitrogen gas or dry inert gas (O2 < 5%) is used to displace oxygen from cargo tanks to prevent flammable atmosphere formation.

6. What is the Maximum Allowable Relief Valve Setting (MARVS) for a Type C independent tank on an LPG carrier?

A. Always negative pressure
B. Exactly 0.0 bar gauge
C. Less than 0.1 bar gauge
D. Greater than 0.7 bar gauge

Answer: D — Greater than 0.7 bar gauge

Type C independent tanks are pressure vessels designed for MARVS usually greater than 0.7 bar gauge (typically 5 to 18 bar gauge for fully pressurized tanks).

7. What risk is associated with rapid liquid cargo release onto steel deck structures?

A. Steel expansion and warping
B. Brittle fracture of hull steel due to extreme cold
C. Corrosion of hull plates
D. Immediate magnetic interference

Answer: B — Brittle fracture of hull steel due to extreme cold

Cryogenic liquids cause severe localized thermal shock and brittle fracture in normal ship steel. Water curtains and deck protection are used.

8. What type of pumps are most commonly used submerged inside LNG cargo tanks?

A. Steam reciprocating pumps
B. Screw positive displacement pumps
C. Submerged electric motor driven centrifugal pumps
D. Diaphragm hand pumps

Answer: C — Submerged electric motor driven centrifugal pumps

Submerged motor centrifugal pumps operate directly submerged in LNG liquid, as methane is electrical insulation in liquid phase with zero oxygen.

9. What instrument measures low concentration flammable gas by catalytic oxidation?

A. Explosimeter (Combustible Gas Indicator)
B. Hydrometer
C. Paramagnetic Oxygen Analyzer
D. Hygrometer

Answer: A — Explosimeter (Combustible Gas Indicator)

Explosimeters measure flammable vapor concentrations as a percentage of the Lower Explosive Limit (LEL).

10. What safety feature automatically trips cargo valves and pumps during an emergency ESD activation?

A. Quick Release Towing Hook
B. Auto-ignition Override
C. Manual Bilge Injection
D. Emergency Shutdown System (ESD)

Answer: D — Emergency Shutdown System (ESD)

The Emergency Shutdown (ESD) system stops cargo pumps, closes ESD valves, and isolates cargo transfer in emergency situations.

11. What is 'rollover' in an LNG cargo tank?

A. Over-rotation of the submerged pump impeller
B. Rapid mixing of two stratified liquid layers of different densities leading to sudden high gas evolution
C. Physical capsizing of the ship
D. Sloshing of cargo causing physical tank deformation

Answer: B — Rapid mixing of two stratified liquid layers of different densities leading to sudden high gas evolution

Rollover occurs when stratified LNG layers equalize densities rapidly, releasing large volumes of boil-off gas and causing sharp tank pressure rise.

12. What is the primary hazard of Ammonia ($NH_3$) when carried on gas tankers?

A. Non-flammable under all temperature conditions
B. High toxicity, corrosive nature, and stress corrosion cracking in steel
C. Zero toxicity and inert behavior
D. High radio-activity

Answer: B — High toxicity, corrosive nature, and stress corrosion cracking in steel

Ammonia is toxic, corrosive to copper alloys, and can cause stress corrosion cracking (SCC) in carbon-manganese steel tanks.

13. What insulation material is widely used in LNG membrane tanks?

A. Reinforced Polyurethane Foam (R-PUF) and Plywood Boxes with Perlite
B. Solid lead sheets
C. Fiber glass wool only
D. Concrete slabs

Answer: A — Reinforced Polyurethane Foam (R-PUF) and Plywood Boxes with Perlite

GTT No.96 uses perlite-filled plywood boxes, while Mark III uses reinforced polyurethane foam insulation panels.

14. What is the function of the water spray system on a gas carrier upper deck?

A. Clean the deck paintwork
B. Provide fresh drinking water to crew
C. Cool cargo tank domes, accommodation boundaries, and absorb toxic or flammable gas leaks
D. Lubricate cargo manifold connections

Answer: C — Cool cargo tank domes, accommodation boundaries, and absorb toxic or flammable gas leaks

Deck water spray systems cool structural steel boundaries and knock down soluble gas clouds (like ammonia) during emergency leaks.

15. Before gas-freeing a cargo tank that contained flammable gas, what step must be taken first?

A. Turn on electric deck heaters
B. Open all deck hatches immediately to fresh air
C. Inert the tank with Nitrogen or inert gas until hydrocarbon content is below LFL
D. Fill the tank with sea water

Answer: C — Inert the tank with Nitrogen or inert gas until hydrocarbon content is below LFL

Purging flammable gas with inert gas prevents the atmosphere inside the tank from entering the flammable range when fresh air is later introduced.

16. What is the purpose of the primary membrane in a Gaztransport membrane LNG containment system?

A. Liquid-tight barrier containing the cargo liquid
B. Outer weather deck protection
C. Thermal insulation layer only
D. Structural hull stiffener

Answer: A — Liquid-tight barrier containing the cargo liquid

The primary membrane (Invar steel or corrugated stainless steel) acts as a thin liquid-tight liquid container.

17. What device is installed on gas carrier vents to prevent flame propagation into cargo tanks?

A. Orifice plate
B. Flame screen or flame arrestor
C. Butterfly valve
D. Non-return flap

Answer: B — Flame screen or flame arrestor

Flame screens use wire gauze to dissipate heat and prevent external flames from entering gas outlets.

18. What is Custody Transfer Measurement System (CTMS) used for on an LNG carrier?

A. Monitoring crew cabin temperature
B. Tracking ship GPS position
C. Calculating engine oil consumption
D. Accurately measuring cargo volume, temperature, and pressure for financial transfer

Answer: D — Accurately measuring cargo volume, temperature, and pressure for financial transfer

CTMS measures liquid level, density, and temperature with high precision for cargo accounting and commercial billing.

19. What is the upper explosive limit (UEL) of methane in air?

A. Approximately 90%
B. Approximately 5%
C. Approximately 50%
D. Approximately 15%

Answer: D — Approximately 15%

Methane is flammable in air between its LEL of ~5% and UEL of ~15% by volume.

20. What personal protective equipment must be worn when sampling toxic liquefied gases?

A. Dust mask and safety shoes
B. Standard cotton coveralls only
C. Sunglasses and leather gloves
D. Full protective suit, SCBA or air-line respirator, and chemical-resistant gloves

Answer: D — Full protective suit, SCBA or air-line respirator, and chemical-resistant gloves

Handling or sampling toxic gases requires respiratory protection (SCBA) and chemical-proof suits to prevent inhalation or contact.

21. What does LPG stand for?

A. Liquefied Petroleum Gas
B. Liquefied Propylene Gasoline
C. Low Pressure Gas
D. Liquid Processed Gas

Answer: A — Liquefied Petroleum Gas

LPG stands for Liquefied Petroleum Gas, primarily consisting of propane and butane mixtures.

22. In a fully refrigerated LPG carrier, at what temperature is propane typically carried at atmospheric pressure?

A. +15 °C
B. −42 °C
C. +5 °C
D. −162 °C

Answer: B — −42 °C

Fully refrigerated LPG carriers carry propane at about −42 °C, its boiling point at atmospheric pressure.

23. What gas detection method is used in continuous gas monitoring systems in interbarrier spaces?

A. Infrared gas absorption analyzers
B. Litmus paper strips
C. Visual observation glass
D. Smoke detectors

Answer: A — Infrared gas absorption analyzers

Infrared gas detectors provide reliable continuous detection of hydrocarbon vapors without needing oxygen.

24. What is the function of the secondary barrier in an LNG containment system?

A. Prevent seawater entry into ballast tanks
B. Provide structural strength to the main deck
C. Hold engine exhaust gas
D. Contain cargo leakage for a specified period if the primary barrier fails

Answer: D — Contain cargo leakage for a specified period if the primary barrier fails

Under the IGC Code, a secondary barrier prevents cold liquid reaching the ship hull structure if the primary barrier leaks.

25. Why must cargo tanks be cooled down gradually before loading cryogenic liquid cargo?

A. Increase loading speed
B. Save electrical power
C. Prevent rust formation
D. Prevent excessive thermal stress and deformation of tank structure and pumps

Answer: D — Prevent excessive thermal stress and deformation of tank structure and pumps

Controlled tank cool-down limits thermal gradients, avoiding structural cracks or seal damages in tanks and piping.

26. What is the typical maximum oxygen content allowed in Nitrogen used for inerting gas tanks?

A. 8.0% by volume
B. 0.5% to 1.0% by volume
C. 15.0% by volume
D. 21.0% by volume

Answer: B — 0.5% to 1.0% by volume

High purity Nitrogen generators on gas tankers supply N2 with O2 levels below 0.5-1% to ensure complete safety.

27. What safety valve is fitted on cargo lines to relieve thermal expansion of trapped liquid?

A. Foot valve
B. Vacuum breaker valve
C. Thermal relief valve
D. Storm valve

Answer: C — Thermal relief valve

Trapped cold liquid expands rapidly when warmed; thermal relief valves release small quantities to prevent pipe rupture.

28. What type of cargo compressor is commonly used in LPG reliquefaction plants?

A. Hydraulic axial pumps
B. Air jet ejectors
C. Wet rotary vane pumps
D. Oil-free screw or reciprocating compressors

Answer: D — Oil-free screw or reciprocating compressors

Reliquefaction units use oil-free compressors to avoid oil contamination of cargo liquid during condensation cycles.

29. What emergency signal activates the shipwide ESD during cargo operations?

A. VHF radio call
B. Manual ESD push button or automatic fire/high pressure trip
C. General emergency alarm bell only
D. Whistle blast on main mast

Answer: B — Manual ESD push button or automatic fire/high pressure trip

ESD pushbuttons located at manifolds, cargo control room, and bridge trigger pneumatic/electrical ESD loops.

30. What publication provides detailed safety guidelines for Tanker Safety in gas operations?

A. COLREG 1972
B. Load Line Convention
C. SIGTTO Liquefied Gas Handling Principles on Ships
D. STCW Code Section A-I/1

Answer: C — SIGTTO Liquefied Gas Handling Principles on Ships

SIGTTO guidelines (Society of International Gas Tanker and Terminal Operators) are industry standard manuals for gas tanker safety.

Set 2 — 30 GASCO exit exam questions with answers

1. What is the primary function of the cargo vaporizer on an LNG carrier?

A. Condense boil-off gas into liquid
B. Separate water from LNG
C. Cool down cargo piping
D. Convert LNG liquid into methane gas for cargo tank gassing-up or boiler fuel

Answer: D — Convert LNG liquid into methane gas for cargo tank gassing-up or boiler fuel

Vaporizers use steam or thermal fluid heat exchangers to vaporize liquid LNG for operational gas supply.

2. Which type of independent tank is spherical in shape and self-supporting?

A. Gaztransport Membrane Tank
B. Integral Tank Type A
C. Technigaz Mark III
D. Moss Rosenberg Type B Tank

Answer: D — Moss Rosenberg Type B Tank

The Moss Rosenberg tank is a spherical self-supporting independent IMO Type B tank; GTT and Mark III are membrane systems.

3. What is 'gassing up' in gas carrier operations?

A. Replacing inert gas in cargo tanks with cargo vapor before initial cool-down
B. Pumping bilge water out
C. Injecting air into cargo tanks
D. Venting excess gas into atmosphere

Answer: A — Replacing inert gas in cargo tanks with cargo vapor before initial cool-down

Gassing up introduces cargo gas vapor to displace inert gas, avoiding N2 freezing or contamination during subsequent liquid loading.

4. What risk occurs if water vapor is present inside an LPG cargo system before loading cargo?

A. Loss of cargo density
B. Ice and hydrate formation blocking valves, filters, and pump suctions
C. Immediate chemical explosion
D. Tank vacuum collapse

Answer: B — Ice and hydrate formation blocking valves, filters, and pump suctions

Moisture forms solid ice and hydrocarbon hydrates at low temperatures, causing severe valve and pump clogging.

5. What instrument is used to check dew point (moisture content) in inert gas?

A. Pyrometer
B. Salinometer
C. Dew point meter / Hygrometer
D. Manometer

Answer: C — Dew point meter / Hygrometer

Hygrometers measure dew point to ensure inert gas moisture content is sufficiently low (typically below -40°C to -60°C dew point).

6. What is the purpose of insulation space purging with Nitrogen on membrane LNG carriers?

A. Maintain inert atmosphere and monitor for gas leakage across primary and secondary barriers
B. Cool down the ship's engine room
C. Clean the steel plating
D. Maintain positive water pressure

Answer: A — Maintain inert atmosphere and monitor for gas leakage across primary and secondary barriers

Nitrogen sweeps through insulation spaces to keep them dry, inert, and continuously sampled by hydrocarbon gas sensors.

7. What is the minimum oxygen concentration required in air for human survival without breathing apparatus?

A. 10.0%
B. 20.9% (at least 19.5% for safe entry)
C. 5.0%
D. 50.0%

Answer: B — 20.9% (at least 19.5% for safe entry)

Normal air contains 20.9% O2. Enclosed space entry requires at least 19.5% to 21% O2 volume.

8. What safety valve opens automatically if cargo tank pressure drops below atmospheric limits?

A. Gate valve
B. Pressure relief valve
C. Globe valve
D. Vacuum relief valve

Answer: D — Vacuum relief valve

Vacuum relief valves protect thin containment tanks from mechanical collapse due to sub-atmospheric internal pressure.

9. What chemical inhibitor is added to unsaturated gas cargoes like Isoprene or VCM to prevent self-reaction?

A. Caustic soda solution
B. Polymerization inhibitor
C. Anti-freeze fluid
D. Rust converter

Answer: B — Polymerization inhibitor

Reactivity inhibitors prevent violent self-polymerization reactions during sea transit.

10. What is the purpose of a cargo hose Emergency Release Coupling (ERC)?

A. Connect different pipe diameters
B. Equalize manifold pressure
C. Speed up liquid loading rates
D. Rapidly detach loading arms/hoses without spill if the ship drifts away from berth

Answer: D — Rapidly detach loading arms/hoses without spill if the ship drifts away from berth

ERCs close dry-break valves and uncouple manifold connections instantly during severe emergency breakaway.

11. What does SIGTTO stand for?

A. Society of International Gas Tanker and Terminal Operators
B. Safety Inspection Group for Tanker Operations
C. Standard International Gas Trade Organization
D. System Integration for Gas Transport Operators

Answer: A — Society of International Gas Tanker and Terminal Operators

SIGTTO promotes safety and operational best practices in gas marine transportation and terminal handling worldwide.

12. What is the density of Methane gas compared to air at standard ambient temperature (+20°C)?

A. Heavier than air
B. Lighter than air (vapor density ~ 0.55 relative to air)
C. Heavier than lead
D. Same density as water

Answer: B — Lighter than air (vapor density ~ 0.55 relative to air)

Methane gas at ambient temperature is lighter than air (~0.55 SG) and disperses upward quickly. Cold methane (-162°C) is initially heavier than air.

13. What type of fire extinguishing agent is most effective on gas cargo manifold fires?

A. Seawater jet directly
B. Sand buckets
C. Foam blanket
D. Dry Chemical Powder (DCP)

Answer: D — Dry Chemical Powder (DCP)

DCP systems (Potassium Bicarbonate/Sodium Bicarbonate) extinguish gas flame jets rapidly by inhibiting chemical chain reaction.

14. Under the IGC Code, what is the maximum filling limit for liquid gas cargo tanks?

A. 80% maximum
B. 50% only
C. Typically 98% at reference temperature to allow thermal expansion
D. 100% full to top

Answer: C — Typically 98% at reference temperature to allow thermal expansion

Filling limits are calculated (usually ~98% max) to ensure liquid expansion does not fill the tank completely 100% liquid-full.

15. What is the function of the cargo heater on a gas tanker?

A. Heat drinking water for crew
B. Warm cold liquid cargo during discharge to atmospheric pressure shore tanks
C. Boil cargo inside cargo tanks
D. Melt ice on ship anchor

Answer: B — Warm cold liquid cargo during discharge to atmospheric pressure shore tanks

Cargo heaters use seawater to warm cold liquid LPG before delivering it to uninsulated pressurized shore storage tanks.

16. What safety document must be completed jointly by ship and shore representatives before starting gas cargo transfer?

A. Crew List
B. Certificate of Registry
C. SSSCL (Ship/Shore Safety Checklist)
D. Bill of Lading

Answer: C — SSSCL (Ship/Shore Safety Checklist)

The ISGOTT/SIGTTO Ship/Shore Safety Checklist ensures all safety controls, ESD links, and emergency communications are verified.

17. What is the primary cause of cold spot formation on the outer hull plating near an LNG tank?

A. Insulation failure or leak in cargo containment
B. Strong wind blowing
C. High seawater salinity
D. Paint discoloration

Answer: A — Insulation failure or leak in cargo containment

Cold spots indicate breakdown in insulation performance, causing hull steel temperature to drop below safe design limits.

18. What protective atmosphere is maintained inside the void spaces of Type A independent LPG tanks?

A. Seawater
B. Steam
C. Dry inert gas or dry air
D. Pure oxygen

Answer: C — Dry inert gas or dry air

Void spaces surrounding Type A tanks are kept dry with inert gas or dry air to prevent corrosion and detect leaks.

19. What device measures cargo level continuously in an LNG membrane tank using radar waves?

A. Radar ullage level gauge
B. Sounding tape
C. Float gauge
D. Sight glass tube

Answer: A — Radar ullage level gauge

Non-contact microwave radar level gauges provide accurate non-mechanical ullage measurements inside cryogenic tanks.

20. What condition requires immediate stopping of gas cargo operations?

A. Electrical storm / lightning in immediate vicinity, ESD failure, or gas leak detected
B. Sunrise
C. Change of watchman
D. Meal time announcement

Answer: A — Electrical storm / lightning in immediate vicinity, ESD failure, or gas leak detected

Lightning storms, cargo leaks, or ESD failures pose immediate fire/explosion risks requiring instant operational shutdown.

21. Deep well pump shaft bearing are cooled and lubricated by liquid

A. Cargo being pumped
B. Hydraulic oil
C. Greas
D. Inert gas

Answer: A — Cargo being pumped

Submerged / deepwell cargo pumps in liquefied gas carriers utilize the liquid cargo being pumped to lubricate and cool the pump bearings and motor windings.

22. The study of behaviour of matter at low temperature is called

A. Seismology
B. Hydrograph
C. Cryogenics
D. Ecology

Answer: C — Cryogenics

Cryogenics is the branch of physics and engineering that studies the production and behavior of materials at extremely low cryogenic temperatures (below -150°C / 123 K).

23. Fixed gas detection system alarms should be activated when the vapour concentration reaches

A. 20
B. 5
C. 30
D. 60

Answer: C — 30

IGC Code 13.6 requires fixed gas detection to alarm at 30% of the LFL of the cargo vapour.

24. A device fitted in gas vent pipeline to arrest the passage of flame Into enclosed space

A. Flame arrestor
B. Explosion proof
C. Flame screen
D. Gas fr

Answer: A — Flame arrestor

A flame arrestor is a safety device fitted in vent lines and pipework designed to prevent the passage of flame into enclosed spaces or cargo tanks by dissipating heat across metallic elements.

25. Chemical combination of flammable substance with oxygen is called

A. Explosion
B. Auto ignition
C. Combustion
D. None of the abov

Answer: C — Combustion

The correct answer is Combustion. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

26. Which cargo operation are to be recorded in cargo record book :

A. All bunker operations
B. All petroleum cargo operations
C. All cargo operations involving NLS
D. All cargo operations

Answer: C — All cargo operations involving NLS

Under MARPOL Annex II, the Cargo Record Book records all cargo operations involving noxious liquid substances.

27. When cargo carried as liquid in cargo tanks and not shipped in drums , containers , or packages , what are they called as

A. Liquid cargo
B. Tank cargo
C. Oil cargo
D. Bulk cargo

Answer: D — Bulk cargo

Cargoes loaded directly into ship tanks without intermediate packaging, drums, or containers are classified as bulk liquid cargoes.

28. Gas ship accommodation and machinery space are :

A. Hazardous area
B. Gas saf
C. Gas dangerous
D. All the abov

Answer: B — Gas saf

Accommodation spaces, engine rooms, and service spaces outside the cargo area are designated as Gas Safe areas provided they are properly segregated and maintained at positive pressure.

29. What is the hazards – reactivity when cargo reacts with water called

A. Hydrate formation
B. Polymerization
C. Toxic vapour
D. None of the abov

Answer: A — Hydrate formation

Hydrate formation occurs when light hydrocarbons (like methane, ethane, propane) combine with free water at low temperatures and high pressures, forming solid ice-like crystalline compounds that can block valves and pipework.

30. Fire fighting technique with a pool fire is to sweep

A. Side to sid
B. Front to back
C. Both A and B
D. None of the abov

Answer: C — Both A and B

When tackling a liquefied gas pool fire with dry chemical powder, the recommended nozzle technique is to sweep side-to-side and advance from front-to-back to extinguish the base of the flame.

Set 3 — 30 GASCO exit exam questions with answers

1. The mass of a Vapour compared with the mass of an equal volume of air both at standard condition to temp and pressure is

A. Relative liquid density
B. Relative vapour density
C. Relative density
D. None of the abov

Answer: B — Relative vapour density

The correct answer is Relative vapour density. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

2. Changing of cargo which may involve

A. Only gas freeing
B. Only inerting
C. Only gassing up
D. All of the abov

Answer: D — All of the abov

A complete change of cargo grades on a gas tanker typically involves stripping/warming up, inerting, gas freeing, aerating (if required), and subsequent gassing up/cooling down.

3. On which type of cargo tank would you find a bimetallic joint or STJ

A. Kvaerner Moss Type B
B. Gas transport membrane
C. Type C
D. Prismatic Type A

Answer: A — Kvaerner Moss Type B

In Kvaerner Moss Type B spherical tank systems, a structural transition joint (STJ or bimetallic joint) connects the aluminum alloy sphere to the stainless/carbon steel supporting skirt.

4. If the cargo density is different from that specified the float gauge manufacturer what will you adjust

A. Float correction
B. Trim correction
C. List correction
D. Tape correction

Answer: A — Float correction

The correct answer is Float correction. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

5. The frequency of pressure testing ashore of BA set should at least every

A. 6 years
B. 5 years
C. 10 years
D. 15 years

Answer: B — 5 years

Self-Contained Breathing Apparatus (SCBA/BA) cylinders must undergo periodic hydraulic pressure testing ashore at least once every 5 years in compliance with SOLAS and class rules.

6. What is the guiding rule for limiting pressure surge on loading or discharging

A. Stop the cargo pump
B. First close ESD valve nearest to the pump
C. Finally close other ESD valv
D. All the abov

Answer: D — All the abov

To minimize hydraulic pressure surge (liquid hammer), ESD valves and pumps follow sequenced shut-down protocols.

7. The ventilation of the airlock should be of the ______ pressure type

A. Negativ
B. Positiv
C. Neutral
D. None of the abov

Answer: B — Positiv

Airlocks providing access between gas-dangerous and gas-safe zones are maintained at positive relative air pressure to prevent vapor ingress into the safe area.

8. Why is it necessary to cool down cargo tanks (refrigerated ships) during bulk loading

A. To avoid overflow
B. To avoid vapors emission
C. To avoid vacuum in cargo tank
D. To avoid excessive tank pressure

Answer: D — To avoid excessive tank pressure

Pre-cooling refrigerated cargo tanks avoids thermal shock, violent flashing, and excessive tank pressure increases during bulk loading.

9. An overdose of toxic petroleum vapour effects your sense of smell by

A. Reducing it temporarily
B. Taking it away completely
C. Improving it temporarily
D. Improving it permanently

Answer: B — Taking it away completely

High concentrations of hydrocarbon vapors and toxic compounds (like H2S) rapidly cause olfactory fatigue, completely deadening the sense of smell.

10. All liquefied gases produces vapours which have a relative vapour density greater than that of

A. Methan
B. Methane and ethylen
C. Methane, ethylene and ammonia
D. None of the abov

Answer: A — Methan

Relative vapor density is the ratio of the mass of a specific volume of gas/vapor compared to an equal volume of dry air at standard temperature and pressure.

11. Gas codes and classification society rules require every tank to be fitted at least _____ level gauge

A. On
B. Two
C. Thr
D. Four

Answer: B — Two

Under the IGC Code (Chapter 13), each cargo tank must be fitted with at least two independent level gauging devices.

12. The concentration of a hydrocarbon gas is air below which there is insufficient hydrocarbon is called

A. Lower flammable limit
B. Dry air
C. Upper flammable limit
D. Stoichiometric ratio

Answer: A — Lower flammable limit

The Lower Flammable Limit (LFL/LEL) is the minimum concentration of flammable gas/vapor in air below which the mixture is too lean to ignite.

13. After stopping the cargo compressor, the glycol/water system is left running to provide

A. Crank case heating
B. Remove cargo vapours
C. Both a and b
D. None of the abov

Answer: C — Both a and b

After shutting down cargo compressors, the glycol-water heating circuit is maintained to provide crankcase heating and prevent condensation or migration of cargo vapors.

14. Fixed water spray system for fire protection purpose in gas tanker covers area such as

A. Cargo tanks domes only
B. The front of the accommodation and control room bulkhead
C. Cargo tank area above deck and cargo manifold area
D. All the abov

Answer: D — All the abov

Fixed water spray systems on gas carriers provide boundary cooling for cargo tank domes, deck piping, manifolds, and accommodation forward bulkheads.

15. When carbon atoms joined by double covalent bonds C-C or triple covalent bonds, what is it called as

A. Saturated organic compound
B. Unsaturated organic compound
C. Both a and b
D. None of the abov

Answer: B — Unsaturated organic compound

Hydrocarbons containing double (C=C) or triple (C≡C) carbon-carbon bonds (such as ethylene and propylene) are classified as unsaturated organic compounds.

16. What is liquid relative density at atmospheric boiling point of methane

A. 0.427
B. 144
C. 195.7
D. None of the abov

Answer: A — 0.427

Methane has a liquid relative density of approximately 0.427 at its atmospheric boiling point of -161.5°C.

17. The ability of a substance to cause damage to living tissue or impairment of the central nervous system

A. Asphyxia
B. Frost bit
C. Toxicity
D. None of the abov

Answer: C — Toxicity

Toxicity is the inherent property of a substance to cause biological damage to living tissue, systemic poisoning, or impairment of the central nervous system.

18. How suction capacity and resulting discharge rate can be regulated

A. By reducing pump speed
B. By throttling the discharge valv
C. By creating bypass (return flow)
D. All the abov

Answer: D — All the abov

Centrifugal cargo pump discharge rate can be regulated by varying motor/turbine speed, throttling the discharge valve, or utilizing recirculating bypass lines.

19. What are the necessary condition that must take place for an electrical discharge to occur

A. Electrostatic separation
B. Electrostatic accumulation
C. Electrostatic discharg
D. All the abov

Answer: D — All the abov

The correct answer is All the abov. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

20. Gas ships cargo compressor room, cargo tank area are

A. Snap back area
B. Gas safe area
C. Gas dangerous
D. All the abov

Answer: C — Gas dangerous

The correct answer is Gas dangerous. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

21. What does Exe represents

A. Flameproof
B. Pressurized
C. Increased safety
D. None of the abov

Answer: C — Increased safety

The Ex 'e' electrical marking designates 'Increased Safety' explosion-protection construction under IEC/CENELEC standards.

22. Onboard LNG tanker which of these requirements is not required for gas burning

A. Vacuum pump
B. Gas heater
C. LD compressor
D. Steam dump on main condenser

Answer: A — Vacuum pump

LNG boil-off gas burning systems utilize LD compressors, gas heaters, and main boiler steam dump systems; vacuum pumps are not part of the fuel gas supply train.

23. What is provided in a low duty gas compressor to prevent lubricating oil mist from entering the compressed LNG vapour ?

A. The gas detection system
B. The gas burning system
C. c. The lubricating system
D. The seal gas system

Answer: D — The seal gas system

A nitrogen seal gas system is fitted on LNG boil-off gas compressors to prevent lubricating oil mist from contaminating the compressed vapor and prevent gas leakage along shaft seals.

24. What is the first task to be completed before doing hot work permit.

A. To inform chief engineer
B. Work can be started without carrying out any other task
C. To complete a hot work permit
D. None of the abov

Answer: C — To complete a hot work permit

Before initiating hot work, a comprehensive hot work permit and risk assessment must be completed, verifying atmosphere tests, safety measures, and formal authorization.

25. The most like place for the spontaneous combustion that take place is

A. The oily rag bin
B. The fuel oil tanks
C. The electrical switch boards
D. The pressuree tanks

Answer: A — The oily rag bin

Oily rags stored in confined bins can undergo slow exothermic oxidation, leading to thermal accumulation and spontaneous combustion.

26. Which of the following is not part of an arrangement in fiber optical system to accommodate 'fail safe' ESDS system

A. The photo coupler of the input side are duplicated
B. Frequency checking sides of O/P are duplicated
C. The optical cables are protected by double layer of insulations
D. The output circuits has double output contacts

Answer: C — The optical cables are protected by double layer of insulations

Fail-safe fibre-optic ESD design duplicates photo couplers, frequency checking and output contacts; double-layer cable insulation is not part of that redundancy arrangement.

27. Up to what temperature is methane vapour heavier than air

A. -110C
B. -161 .5C
C. -125C
D. 15C

Answer: A — -110C

Cold methane vapor at temperatures below -110°C is denser/heavier than ambient air (15°C) and will stay low or form a dense white cloud until warmed above -110°C.

28. What is the typical content of carbon dioxide in inert gas produced by an inert gas generator

A. 25%
B. 15%
C. 20%
D. 30%

Answer: B — 15%

Typical combustion-based marine inert gas generators produce inert gas consisting of ~14-15% CO2, <0.5-1% O2, with the remainder (~84-85%) being nitrogen.

29. A water repellant such as _____ is added in order to avoid humidity in the power

A. Sulphur
B. Silicon
C. Calcium
D. None of the abov

Answer: B — Silicon

Silicon additives and metal stearates are added to dry chemical powders as water repellents to prevent moisture caking and maintain fluid powder discharge.

30. What does the term boil off mean

A. Cargo vapour space in insulation spac
B. Natural vapourization of LNG in the cargo tank
C. Cargo tank vapour pressuree during voyag
D. Excess steam dumped from the boiler

Answer: B — Natural vapourization of LNG in the cargo tank

Boil-Off Gas (BOG) is the continuous natural vaporization of cryogenic liquefied gas (like LNG at -161.5°C) caused by ambient heat ingress through the cargo tank insulation.

Set 4 — 30 GASCO exit exam questions with answers

1. Why LNG is liquefied for sea transportation

A. LNG has high calorific value than natural gas
B. Natural gas transportation by sea is banned
C. It makes it more economical to transport
D. The ship can choose the form of neutral gas or LNG to be loaded

Answer: C — It makes it more economical to transport

Liquefying natural gas reduces its volume by approximately 600 times, making long-distance maritime bulk transportation commercially and technically viable.

2. Which of the following is the typical seal gas system used for low duty gas compressor ?

A. R 404
B. Carbon dioxid
C. Nitrogen
D. Argon

Answer: C — Nitrogen

A nitrogen seal gas system is fitted on LNG boil-off gas compressors to prevent lubricating oil mist from contaminating the compressed vapor and prevent gas leakage along shaft seals.

3. The purpose of remotely controlled measuring of tank levels are to measure

A. Height from liquid surface to top stringers in the tank
B. Height of the liquid in the tank
C. Height from bottom shell to top stringers in the tank
D. Height of bottom girders in the tank

Answer: B — Height of the liquid in the tank

The correct answer is Height of the liquid in the tank. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

4. One of the following is NOT an alarm on an inert gas plant, which one?

A. Low pressuree alarm
B. Low oxygen Alarm
C. Deck sea Low water Alarm
D. Scrubber high water level alarm

Answer: B — Low oxygen Alarm

The correct answer is Low oxygen Alarm. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

5. On all gas ships, any pipework entering or leaving the cargo tank must do so through the ____ of the tank

A. Aft end
B. Top
C. Bottom
D. Forward end

Answer: B — Top

The correct answer is Top. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

6. If a centrifugal pump operating with a positive suction head becomes air bound, your FIRST response should be to _____

A. Vent the casting
B. Tighten the packing
C. Close the discharg
D. Re-prime the pump

Answer: A — Vent the casting

The correct answer is Vent the casting. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

7. How much cleaner is natural gas to burn?

A. Reducing Carbon Dioxide (CO2) emissions by 20% to 30%
B. Reducing carbon monoxide (CO) emissions up to 75%
C. Reducing nitrous oxide (NO2) emission by appropriately 50%
D. All the abov

Answer: A — Reducing Carbon Dioxide (CO2) emissions by 20% to 30%

The correct answer is Reducing Carbon Dioxide (CO2) emissions by 20% to 30%. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

8. Self contained breathing apparatus – SCBA is also called as

A. Compressed air breathing apparatus – CABA
B. EEBD
C. ELSA
D. None of the abov

Answer: A — Compressed air breathing apparatus – CABA

The correct answer is Compressed air breathing apparatus – CABA. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

9. The space enclosed by the ships structure in which a cargo Containment system is situated called ______

A. Hold spac
B. Compressor room
C. Motor room
D. Engine room

Answer: A — Hold spac

The correct answer is Hold spac. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

10. This liquefied gas is normally carried in its fully refrigerated condition at its atmospheric boiling point of -104 °C is ______

A. Ethylen
B. Propan
C. Butan
D. Ammonia

Answer: A — Ethylen

The correct answer is Ethylen. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

11. How is cooling/Cleaning water supplied to the inert gas scrubber tower?

A. By the main sea water pumps
B. By the cargo condenser pump
C. By the scrubber sea water pump
D. By the deck seal sea water pump

Answer: C — By the scrubber sea water pump

The correct answer is By the scrubber sea water pump. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

12. Which safety device is fitted on the deck inert gas line to monitor the supply condition of the inert gas?

A. The inert gas high temperature alarm
B. The inert gas low flow alarm
C. The inert gas low pressuree alarm
D. The inert gas reverse flow alarm

Answer: C — The inert gas low pressuree alarm

The correct answer is The inert gas low pressuree alarm. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

13. What characteristics should insulation materials possess for use in gas carriers?

A. Low thermal conductivity, ability to bear loads
B. Ability to with stand mechanical damagee, lightweight
C. Unaffected by cargo liquid or vapour
D. All the abov

Answer: D — All the abov

The correct answer is All the abov. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

14. Which of the following is the ultimate source of energy for us?

A. LNG
B. Nuclear
C. Solar
D. CNG

Answer: C — Solar

The correct answer is Solar. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

15. Why strainers are commonly installed in the cargo piping system?

A. To protect the cargo handling plant
B. To protect equipment from damagee by foreign objects
C. Both A and B
D. None of the abov

Answer: C — Both A and B

The correct answer is Both A and B. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

16. Which of these would you consider essential equipment to carry when working on the deck of ship carrying ammonia?

A. Gloves
B. Personal O meter
C. Gas mask
D. Personal Hydrocarbon alarm

Answer: C — Gas mask

The correct answer is Gas mask. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

17. What is the condition of inert gas as it is produced by the boilers or inert gas generator?

A. Free of oxygen and clean
B. Hot and containing soot particles
C. Dirty and saturated
D. Super heated and black or greyish in colour

Answer: B — Hot and containing soot particles

Raw inert gas from boiler uptakes or an IG generator is hot and contains soot and SO2; it must be scrubbed and cooled before use.

18. For what reason cargo sampling is necessary in gas tanker?

A. To establish safe conditions prior to cargo transfer
B. To establish that the cargo is within commercially agreed specifications at various Pumps
C. Both A and B
D. None of the abov

Answer: C — Both A and B

The correct answer is Both A and B. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

19. What is the MAIN danger to be guarded against when discharging using a cargo heater with sea water as the heating medium?

A. Over pressureizing of the gas side of the water
B. Freezing of the water side of the heater
C. Over pressureizing of the water side of the heater
D. Overheating of the gas side of the heater

Answer: B — Freezing of the water side of the heater

The correct answer is Freezing of the water side of the heater. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

20. Magnesium, Titanium, Sodium, Lithium and Potassium are classified as

A. Class A fir
B. Class B fir
C. Class C fir
D. Class D fir

Answer: D — Class D fir

The correct answer is Class D fir. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

21. What are the symptoms of Asphyxiant , when LPG and LNG carried as cargo?

A. Increased rate and dept of respiration and loss of consciousness
B. Blueness of the skin (Cyanosis)
C. Stertorous breathing with a snoring sound
D. All of the abov

Answer: D — All of the abov

The correct answer is All of the abov. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

22. Inert gas- How is sea water supplied to the deck seal ?

A. Through the main sea water pumps or through the condenser cargo pump
B. Through a sea water aggregate pump fitted on the cargo deck
C. Through the deck fire lin
D. Through the deck seal pump fitted in the engine room

Answer: D — Through the deck seal pump fitted in the engine room

The correct answer is Through the deck seal pump fitted in the engine room. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

23. On tank vessels, which of these valve types is most commonly used in conjunction with hydraulically actuated controls?

A. Non return valves
B. Globe valves
C. Butterfly valves
D. Gate valves

Answer: C — Butterfly valves

The correct answer is Butterfly valves. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

24. What is critical temperature of methane in °Celsius ?

A. -82.5
B. 82.5
C. 52.8
D. None of the abov

Answer: A — -82.5

The correct answer is -82.5. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

25. On tank vessels equipped with the power operated cargo tank valves, the type of power operator most commonly used is _____

A. Hydraulic
B. Electric
C. Steam
D. Diesel

Answer: A — Hydraulic

The correct answer is Hydraulic. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

26. The valve best suited for throttling gas or liquid flow in a pipe line is the _____

A. Globe valv
B. Gate valv
C. Check valv
D. Pug cock

Answer: A — Globe valv

The correct answer is Globe valv. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

27. What is the boiling point at atmospheric pressure of ammonia

A. -42 °Celsius
B. -34 °Celsius
C. -5 °Celsius
D. None of the abov

Answer: B — -34 °Celsius

Anhydrous ammonia (NH3) has an atmospheric boiling point of -33.4°C (approximately -34°C).

28. Which tanks are completely supported self-supporting and do not form part of the ship's hull structure

A. Independent tanks
B. Membrane tank
C. Semi membranee tank
D. None of the abov

Answer: A — Independent tanks

The correct answer is Independent tanks. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

29. Ammonia forms explosive compounds with

A. Mercury alon
B. Mercury, chlorine, iodine, bromine, calcium, silver oxide and silver hypo chlorit
C. Silica
D. Water

Answer: B — Mercury, chlorine, iodine, bromine, calcium, silver oxide and silver hypo chlorit

The correct answer is Mercury, chlorine, iodine, bromine, calcium, silver oxide and silver hypo chlorit. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

30. A bigger spell of LPG will be visible as a _____ which is condensed water vapour from the atmosphere

A. White cloud
B. Blue cloud
C. Black cloud
D. None of the abov

Answer: A — White cloud

The correct answer is White cloud. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

Set 5 — 30 GASCO exit exam questions with answers

1. How is BOIL OFF gas generated

A. Evaporation
B. Heat ingress
C. Drop in pressure
D. All of the abov

Answer: D — All of the abov

Boil-Off Gas (BOG) is the continuous natural vaporization of cryogenic liquefied gas (like LNG at -161.5°C) caused by ambient heat ingress through the cargo tank insulation.

2. Which of the following can lead to major leak of insulation spaces?

A. Due to hair line cracks inside membranee.
B. Due to significant fatigue cracks on welds of cargo tank membranees
C. The gradual increase of methane content inside the insulation spac
D. Due to accidentally tripped of both HD and LD compressors

Answer: B — Due to significant fatigue cracks on welds of cargo tank membranees

The correct answer is Due to significant fatigue cracks on welds of cargo tank membranees. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

3. Which of the following equipment is not used to lift an auxiliary cargo pump?

A. Electrical connection box
B. Chain block
C. Overhead railing
D. Manifold spool piece derrick

Answer: D — Manifold spool piece derrick

The correct answer is Manifold spool piece derrick. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

4. What will happen to the liquid level within and pressure of a cargo tank when there is a big crack (major leak) in the cargo tank's primary membrane and adjacent insulation space, underneath the cargo level?

A. The liquid level will increase and pressuree will suddenly increas
B. The liquid level will drop and pressuree will suddenly drop
C. The liquid level will drop and pressuree will suddenly ris
D. The liquid level will increase and pressuree will be suddenly drop

Answer: C — The liquid level will drop and pressuree will suddenly ris

With a major leak below liquid level, LNG drains into the insulation spaces, so the tank level drops. The liquid flash-vaporises in the warm insulation and pressure rises suddenly.

5. In the event of major LNG spill which of the following action should not to be taken?

A. Stop cargo operation
B. Inject cargo line with CO2, without stopping the cargo operation
C. Close all accommodation doors and ventilation fans
D. Start the deck water spray (or IMO) pump

Answer: B — Inject cargo line with CO2, without stopping the cargo operation

The correct answer is Inject cargo line with CO2, without stopping the cargo operation. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

6. What is the method used to prevent any further lowering of the hull steel temperature due to damaged insulation?

A. By flooding the ballast tanks with CO2 around the affected cargo tank
B. By sending ship's crew to scaling off the ice formed on the surfaces of the hull steel
C. By injecting nitrogen gas inside the ballast tanks around the affected cargo tank
D. By flooding ballast tanks with sea water around any affected cargo tank

Answer: D — By flooding ballast tanks with sea water around any affected cargo tank

The correct answer is By flooding ballast tanks with sea water around any affected cargo tank. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

7. Which is the melting point temperature of the ESDS automatic fusible element normally fitted onboard?

A. Between 200°C to 206°C
B. Between 50°C to 55°C
C. Between 72°C to 78°C
D. Between 98°C to 104°C

Answer: D — Between 98°C to 104°C

ESDS automatic fusible thermal elements are designed to melt between 98°C and 104°C during a fire, depressurizing the pneumatic loop and tripping the emergency shutdown system.

8. Identify the odd one. Onboard an LNG tanker with NO 96 containment system, which of the following is not a typical early indication of a major cargo leak into the insulation spaces?

A. There will be a rapid increase of methane content in affected areas
B. Relief valve for the affected primary space may lift
C. Inner hull temperature will drop in affected areas
D. There will be cold spots at the ship side close to the affected area

Answer: D — There will be cold spots at the ship side close to the affected area

Methane rise, primary-space relief valve lifting and an inner-hull temperature drop are early signs of a major leak. Cold spots on the outer ship side appear later, if at all, because the ballast space lies in between.

9. Which of the following portable gas meters is used to monitor methane content during the inerting operation prior aerating?

A. M2 test tub
B. Hygrometer
C. Oxygen meter
D. Gas scop

Answer: D — Gas scop

The correct answer is Gas scop. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

10. Onboard a membrane class LNG tanker, during purging cargo tanks with LNG, where is the sampling point for taking the gas readings?

A. Vaporiser outlet sample cock
B. Heater outlet sample cock
C. Vapor line sample cock
D. At cargo tank loading line sample cock

Answer: D — At cargo tank loading line sample cock

When gassing up a membrane tank, LNG vapour (lighter than the inert gas) is admitted at the top through the vapour line and pushes the inert gas out through the bottom filling (loading) line. Readings are therefore taken at the loading-line sample cock until the methane content shows the inert gas has been displaced.

11. Onboard an LNG tanker, why is forced boil - off required out during loaded passage?

A. To maintain cargo tank pressurees
B. To maintain cargo tank temperatures
C. To maintain cold temperature at the tripod mast
D. To supplement fuel supply to the main propulsion plant

Answer: D — To supplement fuel supply to the main propulsion plant

The correct answer is To supplement fuel supply to the main propulsion plant. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

12. If there is an interruption at the end of cooldown before loading, what is the recommended measure to be taken?

A. To stop cooldown completely and open loading valv
B. To stop cooldown and close the vapor manifold
C. To start own spray pump and cool down
D. To continue cooldown process until the tank bottom close to -160°C.

Answer: D — To continue cooldown process until the tank bottom close to -160°C.

The correct answer is To continue cooldown process until the tank bottom close to -160°C.. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

13. Can ballast operations take place during custody transfer measurement?

A. Yes, ballasting should be done to maintain even keel
B. Ship should be maintained upright by ballasting
C. No; all ballast operations should be suspended
D. There are no restrictions on ballast operations

Answer: C — No; all ballast operations should be suspended

The correct answer is No; all ballast operations should be suspended. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

14. What is the medium used for inerting cargo tanks?

A. Oxygen
B. Inert gas
C. Dry air
D. Methan

Answer: B — Inert gas

The correct answer is Inert gas. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

15. What is the main reason for a membrane class LNG tanker to retain a small quantity of cargo ("heel") during ballast passage?

A. To ensure easy starting of cargo pump at loading port
B. To reduce the consumption of heavy fuel oil on passage
C. To avoid bottom of the cargo tank come into contact with oxygen
D. For cold maintenance of the cargo tanks

Answer: D — For cold maintenance of the cargo tanks

Heel is kept to maintain the tanks cold on ballast passage so that they arrive ready to load without lengthy cool-down.

16. Which equipment Is used for evacuating the Insulation spaces?

A. Vacuum pumps
B. HD blowers
C. LD blowers
D. Water ballast ejector

Answer: A — Vacuum pumps

The correct answer is Vacuum pumps. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

17. Safety is dependent on orderliness and cleanliness. Order may be maintained by______.

A. storing items in their assigned plac
B. storing all items in a common storage container except those ready-for-sea
C. tagging all items according to their age and then storing them together
D. disposing of used items

Answer: A — storing items in their assigned plac

The correct answer is storing items in their assigned plac. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

18. Oxygen in the atmosphere of the tank is used up when iron is converted into oxides during the corrosion process. ---------------i in the tanks prior to entry.

A. Copious quantity of fresh air
B. Space to have a minimum oxygen level for sustaining lif
C. Pressurized oxygen pumped
D. Space to be ventilated for 24 hours

Answer: B — Space to have a minimum oxygen level for sustaining lif

The correct answer is Space to have a minimum oxygen level for sustaining lif. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

19. gas pressurizes the liquid out of the soda acid type- water extinguisher through the dip tube.

A. hydrogen
B. oxygen
C. nitrogen
D. carbon-dioxid

Answer: D — carbon-dioxid

Soda-acid fire extinguishers use a solution of sodium bicarbonate in water that reacts with sulfuric acid to generate carbon dioxide expellant gas for Class A fires.

20. Good housekeeping on a vessel prevents fires by

A. allowing better access in an emergency
B. eliminating potential fuel sources
C. eliminating trip hazards
D. improving personnel qualifications

Answer: B — eliminating potential fuel sources

The correct answer is eliminating potential fuel sources. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

21. On each LNG cargo tank two relief valves are fitted. Identify the correct combination of "set pressure" (lifting pressure) and "reseating pressure" for these valves.

A. 250 mbar and 220 mbar
B. 50 mbar and 20 mbar
C. 2.5 bar and 2.2 bar
D. 500 mbar and 200 mbar

Answer: A — 250 mbar and 220 mbar

The correct answer is 250 mbar and 220 mbar. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

22. Advantages of reliquefaction plant on LNG tankships will not include,

A. Total quantity of LNG loaded can be delivered to the customer
B. Reduction in heel required on ballast voyag
C. Lower S0 and NO emissions
D. Proven technology and easy availability of crew

Answer: C — Lower S0 and NO emissions

The correct answer is Lower S0 and NO emissions. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

23. What happens to the air leaving drying tower if the activated alumina inside cylindrical alumina inside cylindrical tank is "old" (inefficient)?

A. It will not be at required dew point
B. It will not be affected at all
C. It will not be warm enough
D. It will not be cold enough

Answer: A — It will not be at required dew point

The correct answer is It will not be at required dew point. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

24. What is provided to ensure that the low duty gas compressor flow rate does not fall below the designed minimum?

A. An automatic shut down system
B. An automatic surge control system
C. An automatic venting system
D. An automatic start system

Answer: B — An automatic surge control system

Centrifugal LD/HD compressors have an automatic anti-surge control that recirculates gas to keep the flow above the surge (minimum) line.

25. Onboard an LNG Tanker, while vaporizing during cargo discharge using the main vaporizer, what is the approximate desired outlet temperature of LNG vapour?

A. -140°C
B. -130°C
C. -10°C
D. -120°C

Answer: C — -10°C

The correct answer is -10°C. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

26. There are typically two types of gas heaters onboard an LNG tanker. One is the main heater and which of the following options is the other?

A. IG heater
B. Fuel gas heater (Boil - off gas heater)
C. Nitrogen heater
D. Air heater

Answer: B — Fuel gas heater (Boil - off gas heater)

The correct answer is Fuel gas heater (Boil - off gas heater). This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

27. A typical membrane method Nitrogen Generator's Air Compressor will trip when the following occur, EXCEPT

A. Nitrogen storage tank pressuree high
B. Air Compressor oil separator pressuree high
C. Air Compressor oil separator inlet temperature high
D. Air Compressor oxygen reading 20% by volum

Answer: D — Air Compressor oxygen reading 20% by volum

About 20-21% O2 is normal for air at the compressor and is not a trip condition; high separator pressure or temperature and high receiver pressure stop the compressor.

28. The following are the communication connection integrated in the ESDS fibre optic system, EXCEPT:

A. 1 connection satellite telephon
B. 1 hotline telephone (to terminal)
C. 1 public telephon
D. 1 normal telephone (to terminal)

Answer: A — 1 connection satellite telephon

The SIGTTO ship/shore fibre-optic link carries ESD signals plus hotline, public and normal telephone lines to the terminal, not a satellite telephone.

29. What is the purpose of having a level gauging system?

A. To avoid over pressureizing of cargo tanks during loading operation
B. To ensure tank cool down rate is maintained at required rat
C. To get accurate tank levels for custody transfer and topping up
D. To prevent sudden temperature change in the insulation spaces

Answer: C — To get accurate tank levels for custody transfer and topping up

The correct answer is To get accurate tank levels for custody transfer and topping up. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

30. What is the type of gas detection system fitted for spaces with air?

A. Spot metering type fixed inside the individual insulation spaces
B. Infrared type using sequential measurement
C. Portable gas detection system due to mobility of this method
D. Catalytic combustion typ

Answer: D — Catalytic combustion typ

Spaces that normally contain air are monitored with catalytic (%LEL) detectors. Inerted insulation spaces use infrared detectors, because catalytic sensors need oxygen.

Set 6 — 30 GASCO exit exam questions with answers

1. What is the "ESDS" abbreviation stands for?

A. Emergency shutdown deck system
B. Emergency system deck serial
C. Emergency shutdown system
D. Emergency downtime system

Answer: C — Emergency shutdown system

ESDS automatic fusible thermal elements are designed to melt between 98°C and 104°C during a fire, depressurizing the pneumatic loop and tripping the emergency shutdown system.

2. How many suitable and operational portable gas detection equipment shall be available onboard?

A. At least two sets with methane gas detection capability
B. At least one with methane and one of carbon monoxides gas detection capability
C. At least one with methane gas and one of Ammonia gas detection capability
D. At least one with methane gas and one of propane gas detection capability

Answer: A — At least two sets with methane gas detection capability

The correct answer is At least two sets with methane gas detection capability. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

3. What is the type of gas detection system fitted to monitor gas content of the insulation spaces?

A. Continuous measurement system using catalytic combustion typ
B. Infrared type / sequential measurement
C. Portable gas detection system due to mobility of this method
D. Spot metering type fixed inside the individual insulation spaces

Answer: B — Infrared type / sequential measurement

The correct answer is Infrared type / sequential measurement. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

4. What is the use of a Distributed Control System (DCS) onboard an LNG carrier?

A. To allow the shore to control the ship's system from the terminal cargo control room
B. To monitor and control main propulsion and cargo operations
C. To monitor and control various cargo equipment distributed on the deck
D. To monitor and control the shore valves from the ship's carao control room

Answer: B — To monitor and control main propulsion and cargo operations

The correct answer is To monitor and control main propulsion and cargo operations. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

5. Which of the following is not a sign of an LNG gas (vapor) leak into insulation spaces?

A. Comparing to normal trends - high temperature variations on barrier spaces
B. Increase of pressuree in insulation spaces
C. Icing of sea water outside hull when ship at anchor
D. Sudden rise in percentage of methane vapour in insulation spaces

Answer: C — Icing of sea water outside hull when ship at anchor

The correct answer is Icing of sea water outside hull when ship at anchor. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

6. How is intrinsic safety achieved for electrical circuits used in hazardous areas?

A. By limiting the ignition energy and surface temperature that can arise during operation
B. By increasing mechanical ventilation to the area
C. By limiting the number of equipment used in a spac
D. By installing machinery which have higher power and thus shorter operation tim

Answer: A — By limiting the ignition energy and surface temperature that can arise during operation

The correct answer is By limiting the ignition energy and surface temperature that can arise during operation. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

7. Why is the 'maximum surface temperature' identified, for electrical equipment used in hazardous areas onboard LNG carriers?

A. The limit is on minimum surface temperature on LNG carriers as the cargo is cryogenic
B. Equipment should operate within these limits to prevent the formation of a hot surfac
C. Equipment should operate within these limits to reduce the power and boil-off consumption
D. Equipment should operate within these limits to reduce the heat transfer to the cryogenic cargo

Answer: B — Equipment should operate within these limits to prevent the formation of a hot surfac

The correct answer is Equipment should operate within these limits to prevent the formation of a hot surfac. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

8. What can major failure of primary membrane lead to?

A. Flooding of primary insulation space by cargo
B. Increase of temperature in pirmary spaces
C. Decrease of gas content in the primary space readings
D. Increase of gas content in secondary spac

Answer: A — Flooding of primary insulation space by cargo

A major primary membrane failure allows LNG to flood the primary insulation space.

9. How will you measure methane concentration inside insulation spaces?

A. By using hydrocarbon meter
B. By using hydrometer
C. By using personnel oxygen meter
D. By using tank scop

Answer: A — By using hydrocarbon meter

The correct answer is By using hydrocarbon meter. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

10. For the LNG NO 96 containment system, why is the cargo tanks secondary insulation spaces pressure maintained slightly higher than primary insulation spaces?

A. To avoid vapor transfer into secondary insulation spaces if primary insulation spaces vapor leaks
B. To avoid cold spot formation in inner hull
C. To reduce heat transfer and increase efficiency of insulation spaces
D. To prevent ingress of air through the leak spot into cargo tank

Answer: A — To avoid vapor transfer into secondary insulation spaces if primary insulation spaces vapor leaks

Keeping the secondary space slightly above primary-space pressure means any leak flows from secondary to primary, so cargo vapour does not migrate into the secondary space.

11. How do you remove water from the secondary insulation space?

A. By using emergency turbine driven pump fitted in secondary insulation spaces well
B. By using vacuum pump fitted inside compressor room
C. By using emergency cargo pump fitted in affected tank emergency cargo pump column
D. By using emergency hand driven pump fitted in primary insulation spaces well

Answer: A — By using emergency turbine driven pump fitted in secondary insulation spaces well

The correct answer is By using emergency turbine driven pump fitted in secondary insulation spaces well. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

12. If insulation damage occurs, how does filling the ballast tanks with sea water help in maintaining the hull steel temperature?

A. Through slow heat transfer, as sea water conducts heat better than air
B. Through better heat transfer, as sea water conducts heat better than air
C. Due to the improved heat transfer to outside sea at ambient temperatur
D. As sea water temperature is much lower than LNG temperature, thus helping the heat transfer

Answer: B — Through better heat transfer, as sea water conducts heat better than air

The correct answer is Through better heat transfer, as sea water conducts heat better than air. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

13. Onboard an LNG tanker with NO 96 containment system, what will happen if a minor membrane leak (crack) occurs above the cargo level?

A. Small flow of liquid into the crack will vaporize. cargo tank pressuree will remain the same.
B. Direct vapor flow rate into the insulation spaces via the crack changes with cargo tank's pressure
C. Cargo pressuree will be tremendously increased boil-off Gas will be out of control
D. Leak will become bigger and primary membranee will collapse inwards

Answer: B — Direct vapor flow rate into the insulation spaces via the crack changes with cargo tank's pressure

A crack above the liquid level lets only vapour into the insulation space, at a flow rate governed by the tank-to-insulation-space pressure difference.

14. International Certificate of fitness for Carriage of Liquefied Gas in bulk will not include,

A. signify that a minimum standard of constructional safety has been incorporated into the ship's build
B. list the cargo grades that the ship is certified to carry
C. the carriage condition or minimum tank temperature that must be maintained
D. the carriage condition for minimum certificated crew that must be maintained.

Answer: D — the carriage condition for minimum certificated crew that must be maintained.

The correct answer is the carriage condition for minimum certificated crew that must be maintained.. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

15. Which code will you refer to for the requirements on LNG containment system?

A. SIGTTO
B. IGC Cod
C. IBC Cod
D. OCIMF

Answer: B — IGC Cod

The correct answer is IGC Cod. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

16. What is the ideal location for the cargo tank from the bottom shell plating, for any Gas Tanker type?

A. B/ 10 or 1.5 meters (4.9 feet), whichever is less
B. B/5 or 3.0 meters (9.8 feet), whichever is less
C. B/ 15 or 2 meters (6.5 feet), whichever isless
D. B/ 4 or 2.4 meters (7.9 feet), whichever is less

Answer: C — B/ 15 or 2 meters (6.5 feet), whichever isless

The correct answer is B/ 15 or 2 meters (6.5 feet), whichever isless. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

17. As per Chapter 11 of IGC code (fire protection and fire extinction) which of the following is a requirement for an LNG tanker?

A. Firemen's outfits
B. Fire ESD system
C. Fire emergency response plans
D. Fire equipment test / drill

Answer: A — Firemen's outfits

IGC Code Chapter 11 (11.6) requires firemen's outfits (personnel protection) on gas carriers.

18. Onboard an LNG carrier, what provisions are made for separation between the deck and electric motors room?

A. Watertight doors
B. Airlocks
C. Air intakes
D. Weathertight doors

Answer: B — Airlocks

The correct answer is Airlocks. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

19. In an LNG carrier mixtures of methane and air are avoided at all times. What is the reason?

A. Dilution of cargo
B. Risk of fire or explosion
C. Degradation of cargo quality
D. Ice formation in cargo

Answer: B — Risk of fire or explosion

Methane-air mixtures within the flammable range (5% to 15% methane by volume) pose severe risks of fire and explosion, so tanks are inerted with inert gas or nitrogen before introducing air or cargo.

20. Which flammability diagram is used to observe change in cargo tank atmosphere for an LNG gas carrier?

A. Methane and nitrogen mixtures
B. Methane and oxygen mixtures
C. Methane and air mixtures
D. Methane, oxygen and nitrogen mixtures

Answer: D — Methane, oxygen and nitrogen mixtures

The correct answer is Methane, oxygen and nitrogen mixtures. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

21. What is the maximum interval of time between sampling and analyzing for each sampling head location sequentially?

A. Not exceeding 50 minutes interval
B. Not exceeding 30 minutes interval
C. Not exceeding 40 minutes interval
D. Not exceeding 60 minutes interval

Answer: B — Not exceeding 30 minutes interval

The correct answer is Not exceeding 30 minutes interval. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

22. How can a gas be liquefied?

A. By mixing gases of higher specific density
B. By the application of pressuree or by cooling
C. By fusion in a closed chamber
D. By evaporation in a closed chamber

Answer: B — By the application of pressuree or by cooling

The correct answer is By the application of pressuree or by cooling. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

23. What is the IGC code definition for a liquefied gas?

A. Product having a saturated vapor pressuree of 2.8 bar absolute at 37.8°C/100°F
B. Product having a saturated vapor pressuree of 1.76 bar absolute at 37.8°C/ 100 ° F
C. Product having a saturated vapor pressuree of 1.76 bar absolute at 38.7°C/1029 F
D. Product having a saturated vapor pressuree of 2.8 bar absolute at 38.7°C/102° F

Answer: A — Product having a saturated vapor pressuree of 2.8 bar absolute at 37.8°C/100°F

The correct answer is Product having a saturated vapor pressuree of 2.8 bar absolute at 37.8°C/100°F. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

24. During heat transfer from one body to another, what transfer takes place?

A. Molecul
B. Energy
C. Power
D. Electron

Answer: B — Energy

The correct answer is Energy. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

25. Why is adequate heel retained during short ballast voyages?

A. It is done as cargo tanks cannot be stripped completely
B. It reduces the ballast to be taken and thus improves turn around
C. It reduces boil-off rates during the ballast voyag
D. It enables loading without further cool down on arrival

Answer: D — It enables loading without further cool down on arrival

Retaining a small heel of LNG cargo on ballast voyages maintains tank cryogenic temperatures, minimizes thermal shock, and avoids lengthy pre-cooling at the loading port.

26. Identify the industry body which is associated with LNG industry although its major stakeholders are from the oil industry?

A. The Oil Companies International Marine Forum (OCIMF)
B. The Oil Charterers International Marine Forum (OCIMF)
C. The Oil & Gas Terminals International Marine Forum (OTIMF)
D. The Oil Terminals International Marine Forum (OTIMF)

Answer: A — The Oil Companies International Marine Forum (OCIMF)

The correct answer is The Oil Companies International Marine Forum (OCIMF). This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

27. Who are the stakeholders represented by the Society of International Gas Tanker & Terminal Operators Ltd (SIGTTO)?

A. Liquefied gas importing countries
B. Liquefied gas shipping and terminals
C. Liquefied gas exporting countries
D. Liquefied gas pipeline owners

Answer: B — Liquefied gas shipping and terminals

SIGTTO (Society of International Gas Tanker and Terminal Operators) represents liquefied gas tanker operators, terminal owners, and industry stakeholders worldwide.

28. Which is the typical temperature trend that indicates a membrane failure?

A. No change in insulation spaces temperature of affected cargo tanks
B. Increase in affected cargo tanks' temperatur
C. Decrease in affected cargo tank's temperatur
D. A decrease in secondary spaces temperature of affected cargo tanks

Answer: D — A decrease in secondary spaces temperature of affected cargo tanks

Cargo leaking past a failed membrane cools the insulation spaces, so a drop in insulation/secondary space temperature indicates membrane failure.

29. What is the use of thermocouples fitted at the surface of the inner hull?

A. To monitor cargo tank temperatur
B. To monitor the inner steel temperatur
C. To monitor hull stresses
D. To monitor inner hull paint thickness

Answer: B — To monitor the inner steel temperatur

The correct answer is To monitor the inner steel temperatur. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

30. What shall be followed upon after a major LNG spill?

A. Nothing to be done to any affected areas
B. All the affected areas shall be sealed off untll next dry dock repairs
C. All the affected areas shall be wash with oil remover
D. All affected areas shall be thoroughly inspected for any signs of cold shock fractures

Answer: D — All affected areas shall be thoroughly inspected for any signs of cold shock fractures

The correct answer is All affected areas shall be thoroughly inspected for any signs of cold shock fractures. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

Set 7 — 30 GASCO exit exam questions with answers

1. What can lead to LNG (cargo) leak into primary insulation spaces?

A. Fatigue crack on ship hull
B. Fatigue cracks on primary membrane
C. Fatigue cracks on secondary membrane
D. Fatigue crack on ballast tank stiffener

Answer: B — Fatigue cracks on primary membrane

The correct answer is Fatigue cracks on primary membrane. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

2. The LNG cargo tank insulation system is designed to perform the following, EXCEPT:-

A. Maintain the boil - off losses from the cargo at an acceptable level
B. Protect cargo valves and piping
C. Protect the inner hull steel from the effect of excessively low temperatur
D. Reduce heat transfer from the outside into cargo tank

Answer: B — Protect cargo valves and piping

The correct answer is Protect cargo valves and piping. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

3. Where is the secondary insulation pump well typically located?

A. Aft of each tank secondary insulation spac
B. Forward of each tank secondary insulation spac
C. Centre of each tank secondary insulation spac
D. Top of each tank secondary insulation spac

Answer: A — Aft of each tank secondary insulation spac

The correct answer is Aft of each tank secondary insulation spac. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

4. Which of the following may not contribute to structural failure of inner hull?

A. Destruction of inner hull due to ship grounding
B. Destruction of ship side due to collision
C. Destruction of Ballast pump during high speed operation
D. Destruction of the insulation space due to sloshing effect

Answer: C — Destruction of Ballast pump during high speed operation

The correct answer is Destruction of Ballast pump during high speed operation. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

5. During a cargo handling operation which of the following precautions need not be observed to deal with spillage?

A. Fire fighting equipment on standby mod
B. Manifold shipside water spray curtain used
C. Ship cordoned off with LNG containment boom
D. Deck fire main on standby mod

Answer: C — Ship cordoned off with LNG containment boom

The correct answer is Ship cordoned off with LNG containment boom. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

6. On an LNG tanker, why ballasting operation is carried out concurrently with LNG discharging operation?

A. To ensure stability criteria is met at all times
B. To ensure vessel has sufficient trim for discharging
C. To ensure easy shore gangway adjustment
D. To maintain manifold alignment with shore marker

Answer: A — To ensure stability criteria is met at all times

The correct answer is To ensure stability criteria is met at all times. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

7. What will happen if cold LNG Boil - Off Gas (BOG) vented through the mast riser?

A. Mast riser will frozen up and it is possible to crack
B. Methane vapor will caught fire immediately
C. Methane vapor will be tuming back to LNG liquid
D. Big white plume will be produced

Answer: D — Big white plume will be produced

The correct answer is Big white plume will be produced. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

8. Traces of inert gas constituents may be present even after aerating. What are the limits for carbon dioxide (CO2) and carbon monoxide?

A. CO2 <1.5% BV and CO <150ppm
B. CO2 <1.5% BV and CO <250ppm
C. CO2 <1.0%BV and CO <50ppm
D. CO2 <0.5% BV and CO <50ppm

Answer: D — CO2 <0.5% BV and CO <50ppm

The correct answer is CO2 <0.5% BV and CO <50ppm. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

9. What should be done before commencing unloading test?

A. Ship should provide specifications to port
B. Exchange of ship - shore safety plan
C. Terminal should provide specifications to port
D. Ship and terminal should test the ship's pumps

Answer: B — Exchange of ship - shore safety plan

The correct answer is Exchange of ship - shore safety plan. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

10. During a long ballast passage which method of retaining heel onboard produces less boil-off?

A. Heel is retained in a center tank and sprayed in others
B. Heel is retained in alternate tanks
C. Heel is retained in 50% of the tanks
D. Adequate heel is retained in all the tanks

Answer: D — Adequate heel is retained in all the tanks

Retaining a small heel of LNG cargo on ballast voyages maintains tank cryogenic temperatures, minimizes thermal shock, and avoids lengthy pre-cooling at the loading port.

11. How do you maintain the cargo tank pressure as low as possible (about 20 - 30 mbar gauge) during inerting operation after gas burning is stopped?

A. by continuous venting via vapor dome's safety valves (manually opened)
B. by continuous venting via vacuum pump mast riser
C. by continuous venting via ship's funnel exhaust
D. by continuous venting via dedicated mast riser

Answer: D — by continuous venting via dedicated mast riser

The correct answer is by continuous venting via dedicated mast riser. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

12. What should be the vessel's trim and list during gauging for custody transfer?

A. Upright and 1 m down by stern
B. Upright and 0.5 m down by stern
C. There are no restrictions trim and list
D. Upright and even keel

Answer: D — Upright and even keel

The correct answer is Upright and even keel. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

13. Fire fighters can control small LNG fire by using____________.

A. water
B. water mixed with ail
C. high expansion foam
D. dry chemical powder

Answer: D — dry chemical powder

The correct answer is dry chemical powder. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

14. Smoke detectors are classified into the following:

A. Photoelectric typ
B. Tonization typ
C. Photoelectric type and Ionization typ
D. Ionization type smoke detectors are in machinery spaces

Answer: C — Photoelectric type and Ionization typ

The correct answer is Photoelectric type and Ionization typ. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

15. Where do the cargo manifold relief lines, the cargo machinery space relief lines and cargo tanks relief lines lead to?

A. They are led to a common riser
B. They are led to gas line to engine room
C. They are led to vapor domes
D. They are led to high duty compressor suction lin

Answer: C — They are led to vapor domes

The correct answer is They are led to vapor domes. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

16. Onboard an LNG tanker, for both main and forcing steam vaporizers it is important to note the output capacity (the amount of LNG liquid turned into LNG vapor). What does this capacity depend on?

A. Cooling water supplied to the vaporizers
B. Heat supplied to the vaporizers (steam supply)
C. Air supplied to the vaporizers
D. Condensate returned from the vaporizers

Answer: B — Heat supplied to the vaporizers (steam supply)

The correct answer is Heat supplied to the vaporizers (steam supply). This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

17. Relief valves are used on an LNG carrier liquid header. Identify the correct combination of "set pressure" (lifting pressure) and "reseating pressure" for these valves.

A. 100 mbar and 900 mbar
B. 10 bar and 9 bar
C. 15 bar and 10 bar
D. 1000 mbar and 500 mbar

Answer: B — 10 bar and 9 bar

The correct answer is 10 bar and 9 bar. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

18. When does the need to rig the auxiliary cargo pump arise?

A. When all the cargo pumps (main and stripping pumps) in a particular tank are out of servic
B. When the needs arise to increase flow rate during discharging operation
C. In case of one cargo pump of the particular tanks is out of servic
D. To increase the loading rate of LNG from shore due to shore pumps is out of servic

Answer: A — When all the cargo pumps (main and stripping pumps) in a particular tank are out of servic

The correct answer is When all the cargo pumps (main and stripping pumps) in a particular tank are out of servic. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

19. Identify the odd one. Which of the following is not an important point to be monitored when using a gas heater?

A. Hot or cold phase flow should be established in the correct sequenc
B. Equipment shall always to be operated in manual mod
C. Heaters shall be pressuree tested prior usage or otherwise checked for leaks at regular
D. Instrumentation and associated equipment should be functioning correctly.

Answer: B — Equipment shall always to be operated in manual mod

The correct answer is Equipment shall always to be operated in manual mod. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

20. Which of the following types LNG carrier propulsion systems will typically have a re-liquefaction plant onboard?

A. Steam turbin
B. Ultra steam turbines
C. Duel - fuel diesel electric (DFDE)
D. Low - speed diesel

Answer: D — Low - speed diesel

The correct answer is Low - speed diesel. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

21. Onboard a membrane class LNG carrier, when is an auxiliary or emergency cargo pump put into use?

A. Total cargo pumps failur
B. One cargo pump failur
C. Two cargo pumps failur
D. Stripping pumps failur

Answer: A — Total cargo pumps failur

The emergency cargo pump is lowered into a tank only when that tank's main cargo pumps have all failed.

22. Which of the following could be a possible cause when the refrigeration compressor "noise" is high?

A. Lubrication oil pressuree high
B. Lubrication oil pressuree low
C. No lubrication oil
D. Compressor suction pressuree low

Answer: B — Lubrication oil pressuree low

The correct answer is Lubrication oil pressuree low. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

23. When ESDS is activated either automatically or manually the following equipment is shutdown on the ship, EXCEPT:-

A. HD compressors
B. Deck air conditioning unit
C. All main and auxiliary cargo pumps
D. All manifold valves. allowed valv

Answer: B — Deck air conditioning unit

ESD stops cargo pumps and compressors and closes the manifold/ESD valves; deck accommodation air conditioning is not part of the ESD shutdown.

24. What is the limitation of a combustible gas detector of catalytic combustion type?

A. It cannot be used for measurement in air
B. It cannot be used for measurement in nitrogen
C. It cannot be used for measurement in methan
D. It cannot be used for measurement in oxygen

Answer: B — It cannot be used for measurement in nitrogen

The correct answer is It cannot be used for measurement in nitrogen. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

25. Following are means of links available onboard to connect ship's ESDS to shore ESDS, EXCEPT:-

A. Pneumatic link
B. Fibre - optical system
C. Bluetooth link
D. Electrical link

Answer: C — Bluetooth link

Ship-shore ESD links are pneumatic, electrical (umbilical) or fibre-optic; Bluetooth is not used.

26. During a fully loaded passage, cold spots are beyond control. It is confirmed that it is unsafe to delay discharge of cargo from the damaged cargo tank. What is the action to be taken?

A. To jettison the cargo via the emergency discharge connection
B. To discharge all the cargo to nearby ballast tank
C. To transfer cargo of the affected tank to other fully loaded tanks
D. To vent out all the cargo via vapor header mast riser

Answer: A — To jettison the cargo via the emergency discharge connection

The correct answer is To jettison the cargo via the emergency discharge connection. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

27. A major failure of the primary membrane will allow LNG to flood the primary insulation space. In addition there will be a tendency for the liquid level in the main cargo tank and a space to equalize. Which of the following is this space?

A. The primary insulation space to equaliz
B. The secondary insulation space to equaliz
C. The both insulation space to equaliz
D. The vapor dome space to equaliz

Answer: A — The primary insulation space to equaliz

Once the primary membrane fails, the cargo tank and the flooded primary insulation space are connected, so their liquid levels tend to equalise.

28. Zone definitions does not include,

A. Zone 0: Area in which an explosive gas atmosphere is present continuously or is present for a long period.
B. Zone 1: Area in which an explosive gas atmosphere is likely to occur in normal operation.
C. Zone 2: Area in which an explosive gas atmosphere is not likely to occur in normal operation, and if it does occur is likely to do so only infrequently and will exit for a short period only.
D. Zone 3: Area in which explosion can occur on a LNGF vessel

Answer: D — Zone 3: Area in which explosion can occur on a LNGF vessel

The correct answer is Zone 3: Area in which explosion can occur on a LNGF vessel. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

29. How is moisture removed from the insulation spaces before a damaged insulation spaces is being repaired?

A. By injecting wet steam into secondary insulation spaces
B. By installing water heater inside the ballast tank
C. By installing bags of activated alumina inside the insulation spaces
D. By drying out the insulation spaces with nitrogen gas

Answer: D — By drying out the insulation spaces with nitrogen gas

The correct answer is By drying out the insulation spaces with nitrogen gas. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

30. Based on the principles of segregation, what would you classify cargo containment system as?

A. Gas dangerous spac
B. Gas dangerous zon
C. Gas safe zon
D. Gas safe spac

Answer: A — Gas dangerous spac

The correct answer is Gas dangerous spac. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

Set 8 — 30 GASCO exit exam questions with answers

1. Based on the principles of segregation, what would you classify the deck of an LNG carrier?

A. Gas dangerous spac
B. Gas dangerous zon
C. Gas safe zon
D. Gas safe spac

Answer: B — Gas dangerous zon

The open cargo-area deck is a gas-dangerous zone (hazardous area) under IGC classification.

2. What is the ideal location for a cargo tank from the shell plating, in any Gas tanker type?

A. less than 760 mm (30 inches) from the shell plating
B. less than 750 mm (29.5 Inches) from the ship sid
C. less than 740 mm (29 inches) from the main deck
D. less than 730 mm (28.7 inches) from the summer draft

Answer: A — less than 760 mm (30 inches) from the shell plating

IGC Code 2.4 requires cargo tanks to be at least 760 mm from the shell plating. Every option says 'less than', so the wording is wrong, but option 0 carries the correct 760 mm figure.

3. Which chapter of the IGC Code refers to the summary of minimum equipment requirements for an LNG carrier?

A. Chapter 18
B. Chapter19
C. Chapter 17
D. Chapter 16

Answer: B — Chapter19

The correct answer is Chapter19. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

4. Which statements is true in accordance with Chapter 15 of the IGC Code?

A. 95% of the total volume of the tank at reference temperatur
B. 96% of the total volume of the tank at reference temperatur
C. 97% of the total volume of the tank at reference temperatur
D. Cargo tanks onboard should not be filled higher 98% of the total volum

Answer: D — Cargo tanks onboard should not be filled higher 98% of the total volum

The correct answer is Cargo tanks onboard should not be filled higher 98% of the total volum. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

5. Exposure controls/personal protection in MSDS will not include,

A. OSHA permissible exposure limit (PEL), Threshold Limit Value (TLV), and any other exposure limit used or recommended
B. Appropriate handling controls
C. Appropriate engineering controls
D. Individual protection measures, such as personal protective equipment.

Answer: B — Appropriate handling controls

The correct answer is Appropriate handling controls. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

6. Which of these is not a possibility if by accident the insulation spaces are over pressurized?

A. Membrane collaps
B. Lifting of insulation safety valves
C. Initiation of emergency shut down
D. Tripping of cargo pump

Answer: D — Tripping of cargo pump

The correct answer is Tripping of cargo pump. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

7. Fire-fighting measures shown in MSDS will not include,

A. Suitable (and unsuitable) extinguishing media
B. Specific hazards arising from the chemical (e.g., nature of any hazardous combustion products)
C. Training requirement for firefighting and Special protective equipment
D. Special protective equipment and precautions for fire-fighters

Answer: C — Training requirement for firefighting and Special protective equipment

The correct answer is Training requirement for firefighting and Special protective equipment. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

8. What should be the typical content of oxygen in inert gas produced by an inert gas generator onboard an LNG carrier?

A. 0.5%
B. 12.6%
C. 7.5%
D. 13%

Answer: A — 0.5%

The correct answer is 0.5%. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

9. If an LNG sale document is marked as Free on Board (FOB), after discharge who is the owner of the "heel' retained onboard?

A. Seller owns the heel and may keep it onboard as he controls the vessel
B. Seller owns the heel and may heel out
C. Buyer owns the heel and may keep it onboard as he controls vessel 6
D. Seller owns the heel and may keep It to mix with the next cargo

Answer: C — Buyer owns the heel and may keep it onboard as he controls vessel 6

Under FOB the buyer takes title at loading and charters/controls the vessel, so the heel after discharge belongs to the buyer.

10. What is the temperature at which gas saturates and the water vapor present begins to condense?

A. Boiling point
B. Condensate point
C. Vapor point
D. Dew point

Answer: D — Dew point

The correct answer is Dew point. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

11. Identify the correct name for a gas or mixture of gases, containing insufficient oxygen to initiate and support combustion where oxygen content is not greater than 5% by volume.

A. Inert gas
B. Cold gas
C. Anti - fire gas
D. Anti - oxygen gas

Answer: A — Inert gas

The correct answer is Inert gas. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

12. What is the designed boil-off rate for a typical membrane type LNG carrier?

A. 0.15% of full cargo tank capacity / day
B. 0.05% of full cargo tank capacity / day
C. 0.25% of full cargo tank capacity / day
D. 0.5% of full cargo tank capacity / day

Answer: A — 0.15% of full cargo tank capacity / day

Typical design BOR for membrane LNG carriers (NO96/Mk III) is about 0.15% of cargo volume per day (newer ships ~0.1%).

13. What is done with Normal Boil - off (NBO) vapour?

A. It is removed to maintain the cargo temperature and pressure
B. It is retained in the tanks as it has no effect
C. It is vented to atmospher
D. It is collected and stored in the buffer tank

Answer: A — It is removed to maintain the cargo temperature and pressure

The correct answer is It is removed to maintain the cargo temperature and pressure. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

14. Which of these factors is not considered when calculating the heel to be retained onboard?

A. Duration of ballast passage
B. Saturated vapor pressuree of the cargo
C. Weather forecast for the loaded passage
D. Level restriction due to sloshing effect

Answer: C — Weather forecast for the loaded passage

Heel is retained to keep the tanks cold on the ballast voyage, so the calculation uses the ballast passage duration, the boil-off (governed by the cargo's vapour pressure and heat ingress) and sloshing fill limits. The weather on the loaded passage plays no part.

15. Onboard a LNG tanker, with NO 96 containment system, what happens to the cargo when a cargo tank suffers a major primary barrier failure?

A. The cargo will flood the primary insulation spac
B. The cargo will flow out to shipsid
C. All the cargo will boil - off immediately
D. The cargo will freeze up

Answer: A — The cargo will flood the primary insulation spac

With NO96, the secondary barrier holds the leak; on primary barrier failure liquid fills the primary insulation space.

16. During a cargo handling operation which of the following precautions need not be observed to deal with spillage?

A. Deck spray pump (IMO) system on standby mod
B. Protective clothing used
C. Constant patrol of cargo area maintained
D. Shore spill team on standby mod

Answer: D — Shore spill team on standby mod

The correct answer is Shore spill team on standby mod. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

17. What is the main danger when discharging a damaged cargo tank in a normal manner?

A. Discharging pump will trip due to debris in the tank
B. Discharging time will be shorter due to lesser cargo in the tank
C. Collapse of secondary membranee due to high differential head
D. Collapse of the primary membranee due to high differential head

Answer: D — Collapse of the primary membranee due to high differential head

The correct answer is Collapse of the primary membranee due to high differential head. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

18. What is the definition for the term "minor failure of membrane?

A. Activation of gas detection equipment for insulation despite of purging with nitrogen
B. Fatigue cracks develop with obvious signs of pressuree rise and the presence of methane vapor
C. Porosity of membranee which allows limited liquid into insulation spaces
D. Minor fatigue cracks, passing liquid into the insulation space and becomes gaseous

Answer: D — Minor fatigue cracks, passing liquid into the insulation space and becomes gaseous

A minor membrane failure is small fatigue cracks/porosity allowing small amounts of liquid into the insulation space where it vaporises and is detected as gas.

19. Onboard an LNG carrier, under what circumstances is purging or gassing up with LNG vapor is critical prior to cool down of cargo tanks?

A. If nitrogen has been used for inerting
B. If inert gas has been used for inerting
C. If time available for cool down is very short
D. If shore supply for cool down is not availabl

Answer: B — If inert gas has been used for inerting

The correct answer is If inert gas has been used for inerting. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

20. In a membrane class LNG tanker, why is the cargo tank pressure increased from 20 mbar g to 150 mbar g at the end of operation?

A. To overcome back pressuree from the vent lin
B. To speed up the inerting process
C. To purge all equipment and pipelines thoroughly
D. To test the tanks prior to aerating

Answer: C — To purge all equipment and pipelines thoroughly

Raising inert gas pressure to ~150 mbarg at the end of inerting is used to pressurise and purge dead ends, equipment and pipelines thoroughly.

21. What is the consequence of ice formation in a cargo tank?

A. Burst in the discharge lin
B. Formation of cold spot in ballast tank
C. Possible damagee to the cargo pump during discharging
D. Icing - up of the discharge pump

Answer: C — Possible damagee to the cargo pump during discharging

The correct answer is Possible damagee to the cargo pump during discharging. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

22. Onboard a membrane class LNG Tanker, what is the ideal tank pressure to be maintained during the warming up operation?

A. Lowest possible pressuree to have good heat transfer process
B. Equal to atmospheric pressuree to allow for free flow of cargo vapor
C. Any pressuree is acceptabl
D. >150 mbar gauge to give good suction for the HD compressors

Answer: D — >150 mbar gauge to give good suction for the HD compressors

During warm-up a relatively high tank pressure increases vapour density, improving heat transfer and HD compressor mass flow.

23. Or the GT NO 96 containment system, what is the recommended cargo tanks inerting operation completion methane content?

A. 5% by volume of methane or mor
B. Less than 3% volume of methan
C. 7% by volume of methane or mor
D. 9% by volume of methane or mor

Answer: B — Less than 3% volume of methan

Inerting after warm-up continues until hydrocarbon (methane) content is below about 2-3% by volume, before aeration.

24. Onboard a membrane class LNG tanker what is the ideal pressure differential to be maintained between the cargo tank and insulation spaces (IS)?

A. IS pressuree < cargo tank pressure
B. IS pressuree > cargo tank pressure
C. IS pressuree = cargo tank pressure
D. IS pressuree = cargo tank pressuree + ibar

Answer: A — IS pressuree < cargo tank pressure

Insulation space pressure must be kept below cargo tank pressure so the membrane is pressed against the insulation and not lifted/collapsed.

25. When using the breathing apparatus, the person is warned of low air volume remaining in his air bottle by the meter needle in the red zone and

A. a whistle sounding off
B. a slight difficulty in breathing
C. the life line being tug 3 times by the outside controller
D. his own judgement of his bottle becoming colder upon emptying

Answer: A — a whistle sounding off

The correct answer is a whistle sounding off. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

26. What is the parameter which influences the separation of nitrogen in a membrane type generator, which uses hollow fiber membranes to produce nitrogen from air?

A. Cooling rate of nitrogen
B. Warming up rate of nitrogen
C. Permeation rate of nitrogen
D. Freezing rate of nitrogen

Answer: C — Permeation rate of nitrogen

Hollow-fibre membranes separate gases by differing permeation rates; O2, CO2 and H2O permeate faster than nitrogen, leaving N2-rich product.

27. The steam heaters onboard LNG tankers work based on "heat transfer" principles. It is important to note the gas volume/liquid volume ratio of LNG at -161.5°C', What is the correct ratio?

A. 161:1
B. 632:1
C. 505:1
D. 404:1

Answer: B — 632:1

The correct answer is 632:1. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

28. Why level gauges fitted onboard LNG carriers are of the "closed" type?

A. It restricts release of liquid or vapor to atmosphere when in us
B. It is cost effectiv
C. It is easy to install
D. It is maintenance -- fr

Answer: A — It restricts release of liquid or vapor to atmosphere when in us

The correct answer is It restricts release of liquid or vapor to atmosphere when in us. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

29. You are in charge of man - entry into an enclosed space. Which of the following will you check using portable gas detectors?

A. Atmospheric pressure
B. Toxicity
C. Dew point
D. Temperatur

Answer: B — Toxicity

The correct answer is Toxicity. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

30. Onboard an LNG carrier in port, the wheelhouse is unmanned. What will be the watch station of the duty cargo officer?

A. Engine control room
B. Cargo control room
C. Electrical equipment room
D. Officer's cabin

Answer: B — Cargo control room

In port the duty cargo officer keeps watch in the cargo control room.

Set 9 — 30 GASCO exit exam questions with answers

1. Onboard an LNG tanker, the main cargo pumps are installed at the bottom of the tripod mast located in the after end of cargo tanks, Which factor should be adjusted to maximize discharge rate?

A. Vapor supply capacity
B. Trim
C. List
D. Gas burning capacity

Answer: B — Trim

The correct answer is Trim. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

2. In ship's ESDS, an automatic electrical system which energizes ESDS due to temperature change of the sensor, fitted at each tank domes and both manifold platforms is known as

A. Automatic fusible elements
B. Automatic push button
C. Infrared gas detection system
D. Automatic heat sensors

Answer: A — Automatic fusible elements

ESDS automatic fusible thermal elements are designed to melt between 98°C and 104°C during a fire, depressurizing the pneumatic loop and tripping the emergency shutdown system.

3. Which of the following will not cause an activation of the ESDS?

A. Differential pressuree between cargo tank and atmosphere - too low
B. Differential pressuree between cargo tank and primary insulation space - too low
C. Differential pressuree between primary and secondary insulation space - too low
D. Manual push button and fusible elements

Answer: C — Differential pressuree between primary and secondary insulation space - too low

ESD triggers include manual buttons/fusible links, low tank pressure and low tank-to-primary IS differential; primary-to-secondary IS differential is normally alarm-only.

4. Where can electrical equipment classified as exib be used?

A. In Zones 0, 1 and 2
B. In Zones 1 and 2
C. In Zones 0 and 2
D. In Zones 0 and 1

Answer: B — In Zones 1 and 2

The correct answer is In Zones 1 and 2. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

5. What is the latest propulsion solution introduced to the LNG shipping industry?

A. Steam turbines
B. Duel - Fuel Diesel Electric (DFDE)
C. Low - speed diesel with a BOG reliquefaction plant
D. Gas turbin

Answer: B — Duel - Fuel Diesel Electric (DFDE)

The correct answer is Duel - Fuel Diesel Electric (DFDE). This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

6. Onboard an LNG carrier, with NO 96 containment system, what will happen when pressure inside primary space is equal to cargo tank pressure?

A. Primary barrier strips will be shifted from its original position
B. Primary barrier strips will be pressed hard onto primary insulation box
C. Primary barrier will collapse inward
D. Nothing will happen - no damagee to primary barrier

Answer: D — Nothing will happen - no damagee to primary barrier

Damage occurs only when IS pressure exceeds tank pressure; at equal pressure the barrier is not stressed.

7. Which are the international bodies that provide regulatory standards for electrical equipment certification?

A. IEEC and CENELEC
B. IEC and CENELEC
C. IEEC and ISO
D. IMO and ISO

Answer: B — IEC and CENELEC

The correct answer is IEC and CENELEC. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

8. After the removal of bulk water from damaged insulation space, Why is it so important to dry out the spaces until the atmosphere dew point is -40°C or lower

A. As there is a possibility for water being trapped and remaining in the insulation spaces
B. As there is a posisbility of mud collected at the bottom of the insulation spaces
C. To cool down the cargo tanks for immediate loading of cargo
D. To avoid the accumulation of rust dust at the bottom of the insulation spac

Answer: A — As there is a possibility for water being trapped and remaining in the insulation spaces

The correct answer is As there is a possibility for water being trapped and remaining in the insulation spaces. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

9. The commercially viable propulsion systems for Deepsea LNG tanker ships will not include,

A. Conventional plant with steam turbines and dual fired boilers
B. Bual-Fuel Diesel Electric (DFDE) plant
C. Slow Speed Diesel with a Boil-Off Gas (BOG) Reliquefaction Plant
D. Medium speed Diesel with a BOG Reliquefaction plant

Answer: D — Medium speed Diesel with a BOG Reliquefaction plant

The correct answer is Medium speed Diesel with a BOG Reliquefaction plant. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

10. What should the Master of an LNG carrier do if the CTS fails?

A. Use the gauging reports of shore receiving tanks.
B. Inform the Company and receivers. Use manual gauging and tank tables
C. Inform the terminal and activate ESD button
D. Suspend cargo operation till CTS is repaired

Answer: B — Inform the Company and receivers. Use manual gauging and tank tables

If the custody transfer system fails, the Master notifies the Company and receivers/terminal and switches to manual gauging with calibrated tank tables, as per CTMS backup procedure.

11. As per IGC Code the "design loads" for a particular cargo containment system, which calculation is a requirement?

A. Crack load
B. Sloshing load
C. Hydrostatic load
D. Damage load

Answer: B — Sloshing load

The correct answer is Sloshing load. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

12. The carriage of LNG cargo requires a certificate for trading called as___________.

A. International Certificate of Fitness for the Carriage of Liquefied Gases in Bulk
B. International Pollution Prevention Certificate for the Carriage of Noxious Liquid Substances in Bulk (NLS Certificate)
C. The International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code), has been mandatory under OLAS chapter VII
D. International Certificate of Fitness for the Carriage of Dangerous Chemicals in Bulk

Answer: A — International Certificate of Fitness for the Carriage of Liquefied Gases in Bulk

The correct answer is International Certificate of Fitness for the Carriage of Liquefied Gases in Bulk. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

13. If an LNG sale document is marked as Delivered Ex Ship (DES), after discharge who is the owner of the 'heel' retained onboard?

A. Heel belongs to the buyer
B. Heel belong to the seller
C. Heel belongs 50% to the buyer and 50% to the seller
D. Heel belongs 75% to the buyer and 25% to the seller

Answer: B — Heel belong to the seller

Under DES the seller provides the ship and title passes only for cargo delivered across the discharge flange; heel retained onboard is not delivered and remains the seller's.

14. At what temperature will methane change from vapour to liquid at atmospheric pressure?

A. -141.5°C
B. -161.5°C
C. -151.5°C
D. -131.5°C

Answer: B — -161.5°C

The correct answer is -161.5°C. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

15. What is the critical temperature and pressure of methane?

A. -145.5°C and 44.7 bars
B. -82.5°C and 47,4 bars
C. -82.5°C and44.7 bars
D. -161.5°C and 47.4 bars

Answer: C — -82.5°C and44.7 bars

The correct answer is -82.5°C and44.7 bars. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

16. Typical inert gas consists of approximately 0.5% Oxygen, 15% Carbon dioxide, 0.5% Carbon monoxide, Oxides of nitrogen and Sulphur dioxide. Which gas forms nearly 84% of the Inert gas?

A. Propan
B. Nitrogen
C. Butan
D. Methan

Answer: B — Nitrogen

The correct answer is Nitrogen. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

17. What are the two main contractual arrangements used in LNG shipping?

A. Delivery Ex - Ship (DES) and Freight On Board (FOB)
B. Delivery Ex - Ship (DES) and Free On Board (FOB)
C. Delivery Ex Shore (DES) and Free On Board (FOB)
D. Delivery On Board (DOB) and Free On Board (FOB)

Answer: B — Delivery Ex - Ship (DES) and Free On Board (FOB)

The correct answer is Delivery Ex - Ship (DES) and Free On Board (FOB). This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

18. Natural and shale gas deposits are not supported by_____________.

A. Conventional and non-associated gas deposits which are called natural gas deposits
B. Natural gas deposits which are much closer to the surface just under the seal
C. Shale gas deposits which are deposits of natural gas found in shale formations.
D. Shale gas deposits which are much less deep than the conventional deposits

Answer: D — Shale gas deposits which are much less deep than the conventional deposits

The correct answer is Shale gas deposits which are much less deep than the conventional deposits. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

19. What is the agreement between the buyer and the end-users called as?

A. Sale and Purchase Agreement(SPA)
B. Delivery Ex-Ship (DES)
C. Gas sale agreement(GSA)
D. Free On Board(FOB)

Answer: C — Gas sale agreement(GSA)

The correct answer is Gas sale agreement(GSA). This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

20. Identify the odd one out. Which of these factors will not increase the boil-off onboard an lng carrier?

A. Detoriation of insulation barriers
B. sloshing in the cargo tanks
C. Rasing of insulation space pressure
D. Long loaded passage

Answer: C — Rasing of insulation space pressure

The correct answer is Rasing of insulation space pressure. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

21. the methods used for producing inert gas onboard LNG carriers are many, which one method may no longer be used?

A. By stoichiometric combustion in an inert gas combustion
B. flue gas from main boilers
C. Nitrogen by fractional distillation or by pressuree swing absorbtion(PSA)
D. Nitrogen by turning liquid nitrogen from shore to nitrogen gas

Answer: B — flue gas from main boilers

The correct answer is flue gas from main boilers. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

22. Which law states that the sum of the partial pressures of the constituent gases of a mixture of gases is equal to the total pressure of the gas mixture?

A. Boyle's law
B. Gay Lussac's law
C. Charles's law
D. Dalton's law of partial pressure

Answer: D — Dalton's law of partial pressure

The correct answer is Dalton's law of partial pressure. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

23. What is the quantity of heat absorbed on vaporization at normal boiling point?

A. Vaporization heat
B. Latent heat
C. Condensation heat
D. lost heat

Answer: B — Latent heat

The correct answer is Latent heat. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

24. During normal loading/ discharging cycle, how does keeping the tanks cool and ready for loading help?

A. It reduces the thermal stresses on the membrane
B. It increases the ship operation costs
C. It increases thermal stresses on the membrane
D. It reduces boil-off in the ballast passage

Answer: A — It reduces the thermal stresses on the membrane

The correct answer is It reduces the thermal stresses on the membrane. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

25. Find the correct answer. A vessel certified to carry an NLS(Noxious liquid substances) must comply with

A. OSHA regulations
B. International Pollution Prevention Certificate for the carriage of Noxious liquid substances
C. STCW regulations
D. ILO regulations

Answer: B — International Pollution Prevention Certificate for the carriage of Noxious liquid substances

The correct answer is International Pollution Prevention Certificate for the carriage of Noxious liquid substances. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

26. Based on the principles of segregation, what would you classify the cargo compressor room?

A. Gas safe spac
B. Gas safe zon
C. Gas dangerous zon
D. Gas dangerous spac

Answer: D — Gas dangerous spac

The correct answer is Gas dangerous spac. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

27. Which of the following are not the early signs of structural failure of the inner hull?

A. Increasing of Lng level in cargo tanks, by incoming seawater
B. Water detected in secondary insulation spac
C. Further lowering of insulation space temperature sensed by the thermocoupl
D. Maximum methane reading detected by the explosive meter inside insulation spaces

Answer: A — Increasing of Lng level in cargo tanks, by incoming seawater

The correct answer is Increasing of Lng level in cargo tanks, by incoming seawater. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

28. Insulation materials for use on liquefied gas carriers shall possess the following, except:

A. ability to bear physical loads
B. Ingress of moisture is not possible thereb, loss of insulation performanc
C. ability to withstands mechanical damage
D. reasonably lightweight

Answer: B — Ingress of moisture is not possible thereb, loss of insulation performanc

The correct answer is Ingress of moisture is not possible thereb, loss of insulation performanc. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

29. How is the formation of cold spots on the inner hull surfaces which is not fitted with thermocouples detected?

A. By using remote ice detection device at any tim
B. frequent inspections of inner hull on ballast passage
C. By using remote lng leak detector any tim
D. frequent inspections of inner hull on loaded passage

Answer: D — frequent inspections of inner hull on loaded passage

The correct answer is frequent inspections of inner hull on loaded passage. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

30. What will happen if the primary space is at least partially flooded with LNG?

A. No reduction in exhaust flow to atmosphere or increase in the temperature of the secondary spaces
B. Changes in exhaust flow to atmosphere and increase in the temperature of secondary spaces
C. Reduction in exhaust to atmosphere or decrease in the temperature of secondary spaces
D. Pressure insulation will increase and temperature for primary spaces will reduces

Answer: A — No reduction in exhaust flow to atmosphere or increase in the temperature of the secondary spaces

The correct answer is No reduction in exhaust flow to atmosphere or increase in the temperature of the secondary spaces. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

Set 10 — 30 GASCO exit exam questions with answers

1. Onboard an LNG tanker with NO 96 containment system, with minor membrane leakage, which of the following it not a recommended remedial action?

A. Check and log gas concentration and temperature on the damageed insulation spaces frequently
B. Ensure at all times secondary space pressuree>damageed primary pressuree +0.5 to 10 bar
C. Alter ship's course and speed to increase pressuree within damageed insulation spaces
D. Check location of crack by using vent cock located on nitrogen supply and exhaust

Answer: C — Alter ship's course and speed to increase pressuree within damageed insulation spaces

In Gaztransport & Technigaz NO 96 membrane containment systems, Invar membranes and perlite insulation boxes maintain cargo containment and thermal insulation.

2. What remedial action should be taken as soon as possible prior discharging cargo from a damaged cargo tank?

A. Fix the equalizer between gas dome and secondary insulation spac
B. Fix the equalizer between gas dome and primary insulation spac
C. Fix the equalizer between primary and secondary spaces
D. Fix the equalizer between gas dome and vacuum lin

Answer: B — Fix the equalizer between gas dome and primary insulation spac

The correct answer is Fix the equalizer between gas dome and primary insulation spac. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

3. Each equipment on LNG ship will be stamped with Information giving the type of protection. That will not include,

A. Ex d IIb T6 means that the equipment is certified Ex d protected by explosion proof enclosur
B. Ex d protected by explosion proof enclosur
C. IIb gas group
D. 17 temperature class -100°C

Answer: D — 17 temperature class -100°C

The correct answer is 17 temperature class -100°C. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

4. Onboard a membrane type LNG carrier, why does the primary membrane have a tendency to collapse during discharge of cargo from damaged cargo tank?

A. Due to different material use for cargo tank and primary membrane
B. Due to temperature variations
C. Due to large different liquid level
D. Due to small different liquid level

Answer: C — Due to large different liquid level

In Gaztransport & Technigaz NO 96 membrane containment systems, Invar membranes and perlite insulation boxes maintain cargo containment and thermal insulation.

5. Which of the following machinery is used for power generation onboard an LNG Carrier with a steam turbine plant?

A. A forcing vaporizer
B. A diesel generator
C. A degasification unit
D. A reliquefaction plant

Answer: B — A diesel generator

The correct answer is A diesel generator. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

6. Onboard an LNG carrier, with NO 96 membrane containment system, what is the indication of failure of the primary membrane and primary insulation space?

A. Temperature drop in secondary space temperature probes
B. Temperature drop in cofferdam space temperature probles
C. Temperature drop in wing ballast tank space temperature probles
D. Temperature drop on main deck temperature probles

Answer: A — Temperature drop in secondary space temperature probes

In Gaztransport & Technigaz NO 96 membrane containment systems, Invar membranes and perlite insulation boxes maintain cargo containment and thermal insulation.

7. How does the gas detection system react to a minor leak of primary barrier spaces?

A. Gas percentage methane content will increase depending on the location and size of the crack
B. Gas percentage oygen content will reduce depending on the location and size of the crack
C. Gas percentage nitrogen content will increase depending on the location and size of the crack
D. Gas percentage methane content will decrease depending on the location and size of the crack

Answer: A — Gas percentage methane content will increase depending on the location and size of the crack

The correct answer is Gas percentage methane content will increase depending on the location and size of the crack. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

8. Which of the following is not a typical counter measure carried out after a major membrane leak or failure?

A. Isolate primary spaces of affected cargo tanks
B. Stop gas burning in boilers
C. Open primary spare exhaust of affected cargo tanks to vent excess pressure
D. Closely monitor all temperature sensors and gas detection system of the affected cargo tank

Answer: B — Stop gas burning in boilers

In Gaztransport & Technigaz NO 96 membrane containment systems, Invar membranes and perlite insulation boxes maintain cargo containment and thermal insulation.

9. Onboard an LNG tanker with NO 96 containment system what will typically happen if a minor membrane leak(crack) occurs below the cargo level?

A. Big flow of liquid into the crack will rapidly vaporize and cargo will be severely damageed
B. Small flow of liquid into the crack will vaporize cargo tank pressuree will increase tremendously increase tremendously
C. Big flow of liquid into the crack will vaporize and colaps the primary membranee inwards
D. Small flow of liquid into the crack will vaporize, cargo tank will remain the sam

Answer: D — Small flow of liquid into the crack will vaporize, cargo tank will remain the sam

In Gaztransport & Technigaz NO 96 membrane containment systems, Invar membranes and perlite insulation boxes maintain cargo containment and thermal insulation.

10. The grade of steel used for inner hull construction is designed so to withstand

A. The main pressuree can be created by UNG voor in an enclosed spac
B. The minimum temperature due to LMG contact
C. The minimun corrosion effect due to steel-air and seawater contact
D. The maximum explosion force that can be created by LNG vapor in an enclosed spac

Answer: B — The minimum temperature due to LMG contact

The correct answer is The minimum temperature due to LMG contact. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

11. Identify the odd one. Each main cargo pump electric motor is protected from certain faults. Which of the following is an exception?

A. Delayed start
B. Thermal overload (over current)
C. Undercurrent (no load operation)
D. Imbalance between phases (single-phasing)

Answer: A — Delayed start

The correct answer is Delayed start. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

12. Why does the cofferdam heating system have two sets of heating coils?

A. One for starboard and one for port
B. One for upper and one for lower
C. One in service and one on standby
D. One for forward part and one for aft part

Answer: C — One in service and one on standby

The correct answer is One in service and one on standby. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

13. In an LNG carrier two types of cargo pumps are fitted in each cargo tank. Identify them by name.

A. Big cargo and small cargo pumps
B. Emergency and small cargo pumps
C. Main cargo and stripping/spray pumps
D. Emergency and big cargo pumps

Answer: C — Main cargo and stripping/spray pumps

The correct answer is Main cargo and stripping/spray pumps. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

14. What are the two types ur heating medium which may be used for the typical cofferdam heating system onboard LNG carers?

A. Seawater or R 404a
B. Steam or glycol water
C. Warm air or brin
D. Alcohol solution or seawater

Answer: B — Steam or glycol water

The correct answer is Steam or glycol water. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

15. Capacitance type gauges are reliable as they have no moving parts. Identify the condition under which they may fall?

A. Presence of nitrogen and methan
B. Presence of water, dirt or rust
C. When the tank is empty
D. When the tank is not full

Answer: B — Presence of water, dirt or rust

The correct answer is Presence of water, dirt or rust. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

16. IGC Requirements on LNG vessels are stated below that will not include

A. The Gas Codes and classification society rules require every cargo tank to be fitted with at least one squid level gaug
B. The Gas Codes require every cargo tank to be fitted with at least two liquid level gauges
C. Chapter 19 of the 1GC code provides the requirements for gauging systems usiing onboard gas carriers.
D. This information is summarized in Appendix 2 of the same code.

Answer: B — The Gas Codes require every cargo tank to be fitted with at least two liquid level gauges

The correct answer is The Gas Codes require every cargo tank to be fitted with at least two liquid level gauges. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

17. In ESDS pneumatic link system which equipment is used to sense and monitor the air pressure in the system so that the ESDS will activate if the air pressure in system Fall below set point

A. Pressure regulator
B. Pressure switch
C. Pressure control valv
D. Pressure dumping valv

Answer: B — Pressure switch

ESDS automatic fusible thermal elements are designed to melt between 98°C and 104°C during a fire, depressurizing the pneumatic loop and tripping the emergency shutdown system.

18. Why should the temperature of cofferdam and liquid domes be maintained above +5°C

A. To ensure no heat transfers from seawater through outer hull
B. To equal The Teperatures of the containment system and insulation spaces
C. to ensure space is warm for inner hull inspection
D. If inner full temperature drops to sub-zero temperatures, it can suffer structural damage

Answer: D — If inner full temperature drops to sub-zero temperatures, it can suffer structural damage

The correct answer is If inner full temperature drops to sub-zero temperatures, it can suffer structural damage. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

19. Where are the spray and stripping pumps normally installed onboard an LNG tanker?

A. At the end of cargo pipes in cargo pump room
B. At main deck close to liquid dome fittings
C. Inside cargo tanks at the bottom end of tripod mast
D. At main deck close to vapor dome fittings

Answer: C — Inside cargo tanks at the bottom end of tripod mast

The correct answer is Inside cargo tanks at the bottom end of tripod mast. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

20. In an Air Dryer Plant in the first stage of drying process the air is cooled to around 5 degree by R 404A refrigeration plant during the second stage what drying agents is used to remove the remaining moisture?

A. Silica gel
B. Activated alumina
C. Perlite
D. Invar powder

Answer: B — Activated alumina

The correct answer is Activated alumina. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

21. When using the main vaporizer to vaporize liquid nitrogen what should be fitted at the inlet of the vaporizer?

A. A removable bend
B. A gas filter
C. A valv
D. A liquid nitrogen detector

Answer: A — A removable bend

The correct answer is A removable bend. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

22. During the nitrogen or cooling cycle in a reliquefaction plant, nitrogen is compressed in 3-stage centrifugal compressor. How is the compressor cooled?

A. Water cooling
B. Propane cooling / Butane cooling
C. Butane cooling
D. LNG cooling

Answer: A — Water cooling

The correct answer is Water cooling. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

23. How should the activated alumina in the drying tank be regenerated after the dry air unit has been in use for sometimes (for about 20 hours) or when the high humidity alarm is given?

A. Shutting down the unit and restart the whole plant
B. Warming up the activated alumina outside the tank
C. Back-flushing hot air through the tank
D. Free flow air through the tank

Answer: C — Back-flushing hot air through the tank

The correct answer is Back-flushing hot air through the tank. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

24. In the LNG re-liquefaction plant, Identify the factor with which the boil-off gas compressor capacity is adjusted automatically?

A. LNG vapour density
B. LNG heat valu
C. LNG Boll-off Rate(BOR)
D. LNG liquid density

Answer: C — LNG Boll-off Rate(BOR)

The correct answer is LNG Boll-off Rate(BOR). This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

25. How is the LNG boil-off gas removed from the cargo tanks brought to the reliquefaction plant?

A. By boll-off gas expanders
B. By low-duty compressors
C. By forcing vaporizer
D. By force draught fans

Answer: B — By low-duty compressors

The correct answer is By low-duty compressors. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

26. What is fitted to at the outlet of main and forcing steam vaporizers to ensure a stable output and avoid accumulation of non-vaporized liquid?

A. Demister
B. Spiral wires
C. A re-evaporator
D. Condensate level controller

Answer: C — A re-evaporator

The correct answer is A re-evaporator. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

27. Normally for an air dryer plant, where possible; "regeneration process must be completed at least two (2) weeks before using the dry air plant. What does this action ensure?

A. Residual heat in the regenerated drier is kept within the plant
B. Residual heat in the generated crier to dissipated
C. Residual heat in the regenerated drier is increased
D. Residual heat in the regenerated drier is not disturbed

Answer: B — Residual heat in the generated crier to dissipated

The correct answer is Residual heat in the generated crier to dissipated. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

28. Why is necessary to purge the auxiliary cargo pump column before the installation can commence?

A. To reduce the tank pressure
B. to ensure the column is filled to the top with cargo
C. To purge out the liquid (cargo) through bottom valve at ensure the column is inerted
D. To purge the air out through bottom valve and ensure column is inerted

Answer: C — To purge out the liquid (cargo) through bottom valve at ensure the column is inerted

The correct answer is To purge out the liquid (cargo) through bottom valve at ensure the column is inerted. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

29. LNG tankship submerged cargo pump running procedure will not include,

A. The cargo pumps may be restarted after a failed start, a maximum of 4 times excluding the failed attempt
B. This procedure must be adhered to as heat build-up from the high starting current may not be carried away during stripping operations
C. This may be due to the lack of liquid flow when (and if) the pump does not prime, due to the extremely low level of LNG during stripping operations
D. Up to 30 seconds of operation with dry suction but with fluid in the discharge pipe will not damagee the pump or the motor

Answer: A — The cargo pumps may be restarted after a failed start, a maximum of 4 times excluding the failed attempt

The correct answer is The cargo pumps may be restarted after a failed start, a maximum of 4 times excluding the failed attempt. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

30. What is an LNG carrier provided with to heat up LNG Vapeur delivered from compressors or vaporizers?

A. Steam heated forcing vaporizers
B. Steam generators
C. Steam heated gas heaters
D. Glycol water heated gas

Answer: C — Steam heated gas heaters

The correct answer is Steam heated gas heaters. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

Set 11 — 30 GASCO exit exam questions with answers

1. Of the two critical equipment of a typical membrane method nitrogen generator, one is the heater. Identify the other from option given

A. Methane analyzer
B. Carbon dioxide analyzer
C. Oxygen analyzer
D. Nitrogen analyzer

Answer: C — Oxygen analyzer

A membrane N2 generator relies on the feed-air heater and the oxygen analyser, which monitors product purity and diverts off-spec nitrogen.

2. Which cargo tank level measuring system is commonly used as a primary system?

A. Radar tank gaug
B. Nitrogen bubbler gaug
C. float gauges
D. steel tape measurements

Answer: A — Radar tank gaug

The correct answer is Radar tank gaug. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

3. Liquefied gas carriers are normally loaded or unloaded through__________situated amidships.

A. Cargo pumps
B. Manifolds
C. stripping pumps
D. ESD valves

Answer: B — Manifolds

The correct answer is Manifolds. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

4. What test is carried out to ensure that all stripping / spray pumps are operational? Hint: this test is is often done after leaving the loading port as it is allows time for installation of an auxiliary cargo pump should it be necessary.

A. Snip test
B. Meggar test
C. cold test
D. load test

Answer: B — Meggar test

The correct answer is Meggar test. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

5. What is the approximate temperature desired on board on LNG tanker, for the output from the forcing vaporizer?

A. -70C
B. -40C
C. -60C
D. -50C

Answer: B — -40C

The correct answer is -40C. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

6. What is the purpose of having a cofferdam heating system?

A. To generate sufficient boil- off to sustain dual fuel firing for the boiler in engine room.
B. To ensure that the cofferdam and liquid domes spaces are at all time kept at +5C when at loaded voyag
C. To increase cargo temperature before arrival at discharge terminal
D. To ensure efficiency of vaporizer operation during the cooling down operation

Answer: B — To ensure that the cofferdam and liquid domes spaces are at all time kept at +5C when at loaded voyag

The correct answer is To ensure that the cofferdam and liquid domes spaces are at all time kept at +5C when at loaded voyag. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

7. Which of the following options is an exception in a typical LNG boil off gas reliquefication plant?

A. cargo cycl
B. forced vaporization
C. nitrogen or cooling vaporization
D. auxiliary cycl

Answer: B — forced vaporization

Boil-Off Gas (BOG) is the continuous natural vaporization of cryogenic liquefied gas (like LNG at -161.5°C) caused by ambient heat ingress through the cargo tank insulation.

8. After extinguishing a paint locker fire using the fixed CO2 system, the next immediate action is for the space to be

A. opened and burned material removed
B. left closed with ventilation off until all boundaries are cool
C. checked for the proper oxygen level
D. opened and doused with water to prevent reflash

Answer: B — left closed with ventilation off until all boundaries are cool

The correct answer is left closed with ventilation off until all boundaries are cool. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

9. which of the following conditions can contribute to accidents ?

A. good housekeeping
B. inspections
C. unsafe conditions
D. intelligent work habits

Answer: C — unsafe conditions

The correct answer is unsafe conditions. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

10. which chemical is used to treat water in order to ensure its safety for drinking?

A. nitrogen
B. chlorin
C. carbon
D. oxygen

Answer: B — chlorin

The correct answer is chlorin. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

11. what is the typical measuring range for an oxygen analyzer?

A. 10ppm volume oxygen in air
B. 0- 25% volume oxygen in air
C. 0-5% volume oxygen in air
D. 0-100% volume oxygen in air

Answer: B — 0- 25% volume oxygen in air

The correct answer is 0- 25% volume oxygen in air. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

12. What is typically the first action taken when there is a serious primary membrane leak?

A. Equalize the primary insulation space and vapor dome pressurees of the affected cargo tank
B. Stop filling the affected cargo tank's primary insulations with nitrogen
C. open up the affected cargo tank's primary insulations with inspection
D. Warming up the affected cargo tank immediately

Answer: A — Equalize the primary insulation space and vapor dome pressurees of the affected cargo tank

In Gaztransport & Technigaz NO 96 membrane containment systems, Invar membranes and perlite insulation boxes maintain cargo containment and thermal insulation.

13. On an LNG tanker, during discharging why is it necessary to maintain the trim of 3m by stern during final discharging before completion of bulk discharge?

A. To ensure proper draining of ballast water from ballast tank
B. to increase boil-off of cargo while discharging
C. to ensure maximum discharge of cargo prior to warming up of cargo tanks
D. to maximize boil-off of cargo with by increased exposed surface area

Answer: C — to ensure maximum discharge of cargo prior to warming up of cargo tanks

The correct answer is to ensure maximum discharge of cargo prior to warming up of cargo tanks. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

14. Onboard an LNG carrier, during loading operations, why should be- ballasting be done concurrently with loading?

A. to reduce vessel turnaround tim
B. to keep the vessel within the required limit of draft, trim, stress and stabilty
C. to ensure that the gangway is safe for use at all times
D. deballasting can be done after 50% loading is complet

Answer: B — to keep the vessel within the required limit of draft, trim, stress and stabilty

The correct answer is to keep the vessel within the required limit of draft, trim, stress and stabilty. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

15. What is the average recommended cooling down rate of cargo tanks?

A. 20-22 °C/ hour
B. 10-12 °C/ hour
C. 30-32 °C/ hour
D. 40-42 °C/ hour

Answer: B — 10-12 °C/ hour

The correct answer is 10-12 °C/ hour. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

16. What is the objective of drying cargo tanks?

A. to warm the cargo tanks prior to inerting
B. to remove methane residual
C. to prevent damagee of cargo equipment
D. to reduce moisture content

Answer: D — to reduce moisture content

The correct answer is to reduce moisture content. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

17. Onboard an LNG carrier, during loading operation which is the correct sequence of liquid flow during loading operation?

A. terminal- spary line- main liquid line- tank filling val
B. terminal- manifold crossover- main liquid line- tank filling val
C. terminal- manifold crossover - main vapor line- tank filling val
D. terminal-manifold crossover - main liquid line- spary lin

Answer: B — terminal- manifold crossover- main liquid line- tank filling val

The correct answer is terminal- manifold crossover- main liquid line- tank filling val. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

18. Where is the cargo tanks warming up operation normally carried out?

A. in port when alongside as this is a routine, non-critical operation
B. it can be done anywhere but at sea as shore support is required
C. in sheltered waters where the mixture can be exhausted without danger
D. it is done after entry into the drydock

Answer: C — in sheltered waters where the mixture can be exhausted without danger

The correct answer is in sheltered waters where the mixture can be exhausted without danger. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

19. Onboard an LNG carrier, why should CO2 which may freeze be removed prior to cool down?

A. oxygen in the CO2 can form an explosive mixture with LNG
B. at 60 °C CO2 freex=zes to form a powder which can block line components
C. to increase cargo carrying capacity
D. to prevent corrosive effect of CO2 / lng mixtur

Answer: B — at 60 °C CO2 freex=zes to form a powder which can block line components

The correct answer is at 60 °C CO2 freex=zes to form a powder which can block line components. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

20. In membrane class LNG carriers, what is the expected changes in the primary insulation space during the cooldown?

A. pressuree rises due to increase in tank wall temperatur
B. pressuree drops due to fall in tank wall temperatur
C. pressuree is not affected by tank cooldown
D. pressuree rises then drops

Answer: B — pressuree drops due to fall in tank wall temperatur

In Gaztransport & Technigaz NO 96 membrane containment systems, Invar membranes and perlite insulation boxes maintain cargo containment and thermal insulation.

21. All pipelines associated with cargo have to be purged with ig for at least for 5 min, which of these does not require purging with IG?

A. fuel gas heaters pipelines
B. insulation space lines
C. hd & ld gas compressors discharge lin
D. vapor and liquid manifolds

Answer: B — insulation space lines

The correct answer is insulation space lines. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

22. On an Lng tanker during the initial stage of cooling down operation, prior discharging why is it necessary to open the main loading valves of the forward and the aft cargo tanks?

A. to ensure liquid flow into the forward and aft cargo tanks
B. to increase the pressuree in the cargo tanks before discharging
C. to clean anhy impurities in the pipelines before discharging
D. to purge the vapor which remains at both ends of the liquid header

Answer: D — to purge the vapor which remains at both ends of the liquid header

The correct answer is to purge the vapor which remains at both ends of the liquid header. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

23. For the gt no. 96 containment system, what is the recommended inlet temperature of warm LNG vapor into the cargo tanks?

A. -80 °C
B. +80 °C
C. +120 °C
D. +20 °C

Answer: B — +80 °C

The correct answer is +80 °C. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

24. ONboard LNG tanker, why is it necessary to maintain gas burning during loaded passage?

A. to maintain/ control cargo tank pressuree and prevent venting
B. to minimize heavy fuel oil consumption
C. to maintain constant pressuree in the insuation spaces
D. to maximize quantity of boil- off use in boiler

Answer: A — to maintain/ control cargo tank pressuree and prevent venting

The correct answer is to maintain/ control cargo tank pressuree and prevent venting. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

25. What is cargo capacity to which an LNG carrier's cargo tanks can be safety loaded?

A. 95% of total cargo tank capacity of the vessel
B. 98.5% of total cargo tank capacity of the vessel
C. total capacity available in cargo tank
D. spare available for cargo after reduction of vapour spac

Answer: B — 98.5% of total cargo tank capacity of the vessel

The correct answer is 98.5% of total cargo tank capacity of the vessel. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

26. During cool down when" free flow " of gas, from cargo tanks to shore, is not effective and cargo tanks pressure increases, what is the best solution?

A. start ld compressor and return gas to shor
B. start hd compressor and return gas to shor
C. increase the set point of common raiser vent setting
D. shut the vapor manifold valv

Answer: B — start hd compressor and return gas to shor

The correct answer is start hd compressor and return gas to shor. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

27. How is the cool down of cargo tanks done?

A. lng is introduced through the loading lin
B. lng is sprayed into the tanks via the sprayer rings
C. lng vapor is let in through the vapor dom
D. insulation spaces are cool down with nitrogen

Answer: B — lng is sprayed into the tanks via the sprayer rings

The correct answer is lng is sprayed into the tanks via the sprayer rings. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

28. What is the normal in service operating pressure difference between the primary and secondary insulation spaces?

A. primary IS pressuree = secondary IS pressure
B. primary IS pressuree > secondary IS pressure
C. secondary IS pressuree = primary IS pressuree +1-2mbar
D. primary IS pressuree = secondary IS pressuree +1-2mbar

Answer: C — secondary IS pressuree = primary IS pressuree +1-2mbar

The correct answer is secondary IS pressuree = primary IS pressuree +1-2mbar. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

29. For the membrane class LNG carrier, during drying operation what is the recommended differential pressure between primary insulation space and cargo tank?

A. tank pressuree< IS pressuree +10mbar
B. tank pressuree > IS pressuree +10mbar
C. any pressuree can be maintained
D. tank pressuree = IS pressuree +10mbar

Answer: B — tank pressuree > IS pressuree +10mbar

In Gaztransport & Technigaz NO 96 membrane containment systems, Invar membranes and perlite insulation boxes maintain cargo containment and thermal insulation.

30. On an lng tanker, during discharging why should stripping pumps be started at a minimum of 0.5m?

A. to ensure pump tripped at a correct level
B. to avoid difficulty in priming the pumps
C. to ensure sufficient current is available when starting the pump
D. to reduce discharging time in port

Answer: B — to avoid difficulty in priming the pumps

The correct answer is to avoid difficulty in priming the pumps. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

Set 12 — 30 GASCO exit exam questions with answers

1. On an lng tanker, during discharging which of the following is not a reason for opening the cargo discharge valve to about 10-20% before starting of cargo pump?

A. to avoid vapor lock "bang" at discharge line curve before the valv
B. to achieve optimum flow rate of the pump
C. to avoid damagee to te cargo discharge valv
D. to avoid low current trip

Answer: B — to achieve optimum flow rate of the pump

The correct answer is to achieve optimum flow rate of the pump. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

2. Why is energy transfer calculated during lng cargo transfer and not just volume of transfer?

A. lng is sold on the basis of heating valu
B. lng being a gas, volume measured is incorrect
C. lng being a cyrogenic liquid volume measured is incorrect
D. it is only done if receiver demands it

Answer: A — lng is sold on the basis of heating valu

The correct answer is lng is sold on the basis of heating valu. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

3. Onboard lng carrier, what is the maximum allowable filling limit as per the IMO/ IGC regulation?

A. 98.5%
B. 98.6%
C. 98%
D. 99%

Answer: C — 98%

The correct answer is 98%. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

4. Onboard a LNG tanker, with NO 96 containment system, which valves are used to maintain the pressure within the primary and secondary insulation spaces?

A. Manifold esd valves
B. nitrogen make up and exhaust control valv
C. discharging valves in liquid dom
D. insulation space relief control valv

Answer: B — nitrogen make up and exhaust control valv

In Gaztransport & Technigaz NO 96 membrane containment systems, Invar membranes and perlite insulation boxes maintain cargo containment and thermal insulation.

5. On an lng tanker, during discharging which of the following is not required to ensure the optimum performance of a main cargo pump?

A. monitor the discharge pressure
B. monitor the load current
C. adhere to its performance curv
D. keep adjusting the low current trip set-point

Answer: D — keep adjusting the low current trip set-point

The correct answer is keep adjusting the low current trip set-point. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

6. On an lng tanker why do we need to maintain vapor arm connected to shore even after completion of discharging until just before sailing?

A. to increase tank pressuree by getting gas from shor
B. to manage tank pressuree in case of ship gas burning failur
C. to drain remaining liquid to shor
D. to ensure proper sequence before disconnection

Answer: B — to manage tank pressuree in case of ship gas burning failur

The correct answer is to manage tank pressuree in case of ship gas burning failur. This complies with established gas tanker operational standards, thermodynamics, and the IGC Code safety requirements.

7. Onboard a membrane class LNG tanker, what is the typical gas heater outlet temperature control set at, during inerting operation using nitrogen?

A. 0 °C
B. -130 °C
C. -20 °C
D. +20 °C

Answer: C — -20 °C

In Gaztransport & Technigaz NO 96 membrane containment systems, Invar membranes and perlite insulation boxes maintain cargo containment and thermal insulation.

8. On a membrane class LNg tanker upon completion of cargo how is it remaining liquid in the discharging arm drained?

A. By injecting nitrogen from shore to ship trimmed by stern
B. by opening one of thr aft cargo tanks loading valve with ship trimmed by stern
C. by opening drain valve at the manifold connection with ship trimmed by head
D. by opening all discharge valves and drain back into the cargo tanks with ship kept even keel

Answer: B — by opening one of thr aft cargo tanks loading valve with ship trimmed by stern

In Gaztransport & Technigaz NO 96 membrane containment systems, Invar membranes and perlite insulation boxes maintain cargo containment and thermal insulation.

9. For the GT NO 96 containment system what is the recommended cargo tank warming up operation completion temperature?

A. Equal to outside air temperatur
B. Above +30 °C
C. Above +10 °C
D. Above -130 °C

Answer: C — Above +10 °C

In Gaztransport & Technigaz NO 96 membrane containment systems, Invar membranes and perlite insulation boxes maintain cargo containment and thermal insulation.

10. Accidental release measures in an MSDS will NOT include ____.

A. Personal precautions, protective equipment and emergency procedures
B. Methods and materials for containment and cleaning up
C. Environmental precautions
D. Instructions for informing the authorities of an accidental release

Answer: D — Instructions for informing the authorities of an accidental release

Section 6 of a GHS-format SDS (accidental release measures) covers personal precautions, protective equipment and emergency procedures, environmental precautions, and methods and materials for containment and clean-up. Reporting obligations come from regulations and company procedures, not this section.

11. What is the gas group classification of an LNG carrier, based on the gas likely to be present in its hazardous spaces?

A. Group IIC
B. Group IIB
C. Group I
D. Group IIA

Answer: D — Group IIA

LNG is mainly methane, which is classified in apparatus gas group IIA under IEC 60079. Group IIB covers gases such as ethylene and IIC covers hydrogen and acetylene; Group I is reserved for mining (firedamp).

12. Which IEC symbol denotes explosion-proof (flameproof) electrical protection?

A. Ex e
B. Ex d
C. Ex n
D. Ex p

Answer: B — Ex d

Ex d is the flameproof or explosion-proof enclosure, which can withstand an internal explosion and prevent its transmission to the outside atmosphere. Ex e is increased safety, Ex p pressurised and Ex n non-sparking protection.

13. Which of these statements about primary cells is correct?

A. Used primary cells can be recharged
B. Used primary cells can be refilled and reused
C. Used primary cells have to be discarded
D. Used primary cells regain capacity if left idle for a week

Answer: C — Used primary cells have to be discarded

Primary cells such as zinc-carbon and alkaline batteries rely on an irreversible chemical reaction, so once discharged they cannot be recharged or refilled and must be disposed of properly. Rechargeable batteries are secondary cells.

14. How should steam pipes be protected in machinery spaces?

A. They should be painted in different colours
B. They should have placards to warn personnel
C. They should be lagged
D. They should be kept wet to cool them

Answer: C — They should be lagged

Steam pipes are lagged (insulated) to protect personnel from burns, reduce heat loss and keep hot surfaces away from oil leaks. SOLAS II-2/4.2 requires hot surfaces over 220°C that could be contacted by oil to be insulated.

15. What is the least you must do before entering a cofferdam in the engine room?

A. Open up the manhole and enter the cofferdam
B. Complete an enclosed space entry checklist
C. Enter the cofferdam and simultaneously start ventilation
D. Put on a dust mask and enter

Answer: B — Complete an enclosed space entry checklist

A cofferdam is an enclosed space. SOLAS XI-1/7, IMO Res. A.1050(27) and the SMS require an entry permit and checklist covering ventilation, atmosphere testing, isolation and rescue arrangements before anyone enters.

16. What is the least a person should do before entering machinery spaces?

A. Wear appropriate personal protective equipment
B. Inform the bridge
C. Inform his superiors
D. Remove his safety shoes

Answer: A — Wear appropriate personal protective equipment

Machinery spaces involve noise, heat, rotating parts and slippery surfaces. As a minimum, anyone entering must wear suitable PPE such as a boiler suit, safety shoes, helmet and ear protection, as required by the Code of Safe Working Practices.

17. Your vessel has completed loading and is ready for gauging. Which of the following should you ensure?

A. All cargo systems on the ship are closed and the shore connections isolated or disconnected
B. All personnel are on board and ready at their departure stations
C. The custody transfer system is closed and isolated in the presence of shore representatives
D. Cargo system valves are lined up to fill the largest tank to allow topping-up

Answer: A — All cargo systems on the ship are closed and the shore connections isolated or disconnected

Custody transfer gauging must be done with the cargo system static. All ship cargo valves are closed and the shore connections isolated or disconnected so that no liquid or vapour can move between ship and shore while levels, temperatures and pressures are recorded.

18. With a pneumatic ship/shore link, what happens when the ship moves off the jetty beyond its safe working limits?

A. The air hose breaks
B. The air pressure in the link drops
C. Alarms sound and the ESD is activated
D. All of the above

Answer: D — All of the above

In a pneumatic ship/shore ESD link the air hose is designed to part if the ship drifts beyond the safe envelope. The resulting loss of air pressure trips the system, sounding alarms and activating the emergency shutdown of cargo transfer.

19. The heat used in the process of evaporation is called ____.

A. Latent heat
B. Sensible heat
C. Potential heat
D. Specific heat

Answer: A — Latent heat

Latent heat is the heat absorbed or released during a change of state without any change in temperature. During evaporation the liquid absorbs latent heat of vaporization, which is how boil-off cools a liquefied gas cargo.

20. Pressure measured above a perfect vacuum is called ____ pressure.

A. Absolute
B. Atmospheric
C. Gauge
D. Differential

Answer: A — Absolute

Absolute pressure is measured from a perfect vacuum, or zero pressure. Gauge pressure is measured relative to the local atmospheric pressure, so absolute pressure equals gauge pressure plus atmospheric pressure.

21. What is the typical expansion ratio of high-expansion foam?

A. Up to about 1000:1
B. 5:1 to 12:1
C. 1:1 to 3:1
D. Above 5000:1

Answer: A — Up to about 1000:1

Foam is classed by expansion ratio. Low-expansion foam is up to about 12:1, medium-expansion foam is in the tens to around two hundred, and high-expansion foam reaches up to about 1000:1, which allows it to fill enclosed spaces such as engine rooms quickly.

22. The function of a cargo tank pressure relief valve is to ____.

A. Release excessive pressure from the tank
B. Measure the liquid level in the tank
C. Supply inert gas to the tank
D. Prevent liquid entering the vapour header

Answer: A — Release excessive pressure from the tank

IGC Code Chapter 8 requires each cargo tank to have pressure relief valves set at or below the MARVS. When tank vapour pressure rises above the set point, the valve lifts and vents vapour to the vent mast, protecting the tank from overpressure.

23. What medium is used for the initial pressurization of insulation spaces?

A. Nitrogen
B. Oxygen
C. Methane gas
D. Dry air

Answer: A — Nitrogen

Insulation and inter-barrier spaces of membrane LNG tanks are filled and pressurized with dry nitrogen, which is inert and has a very low dew point. This prevents a flammable atmosphere and condensation or ice in the insulation, and allows leaks to be detected.

24. What happens in an air dryer plant when the seawater flow to the refrigerant condenser is insufficient?

A. The air is not cooled enough at the outlet
B. The air is over-cooled at the outlet
C. The moisture in the air freezes at the outlet
D. The air outlet temperature is not affected at all

Answer: A — The air is not cooled enough at the outlet

With insufficient cooling water the refrigerant condenser pressure rises and the refrigerating capacity falls. The process air is then not cooled enough, less moisture condenses out, and the dew point of the dried air rises.

25. What is required to enable BOG to be burned in the event of a reliquefaction plant shutdown on an LNG carrier?

A. Gas Combustion Unit (GCU)
B. Steam dump plant
C. Degasification plant
D. Steam boiler

Answer: A — Gas Combustion Unit (GCU)

On ships with reliquefaction plants and diesel propulsion, a Gas Combustion Unit is fitted to dispose of excess boil-off gas safely when the reliquefaction plant is stopped or the engines cannot consume it, keeping tank pressure within limits without venting.

26. In a Moss-type LNG cargo tank, what is the annular (hold) space filled with to avoid fire risk?

A. Inert gas
B. Moist air
C. Oxygen
D. Dry air

Answer: A — Inert gas

The hold space around a Moss spherical tank is filled with dry inert gas so that any cargo leak cannot form a flammable mixture. Being dry, it also prevents condensation and ice on the cold tank insulation, and gas detection monitors it for leaks.

27. In an LNG Sale and Purchase Agreement, who is responsible for transportation of the LNG by sea?

A. Either the buyer or the seller, as agreed in the contract
B. The seller, always
C. The buyer, always
D. Members of SIGTTO only

Answer: A — Either the buyer or the seller, as agreed in the contract

Responsibility for shipping depends on the delivery terms agreed in the SPA. Under FOB the buyer arranges the ship, while under DES or CIF the seller does, so transportation can fall to either party.

28. The pipeline connecting the vapour spaces of the shore tank and the ship during cargo transfer is called the ____.

A. Vapour return line
B. Vapour escape line
C. Liquid crossover line
D. Stripping line

Answer: A — Vapour return line

During loading, vapour displaced from the ship's tanks is sent back to the shore tank through the vapour return line, and during discharge the flow is reversed. This balances pressures and avoids venting cargo vapour to atmosphere.

29. The sum of gauge pressure and one atmosphere gives the ____ pressure.

A. Absolute
B. Atmospheric
C. Gauge
D. Vacuum

Answer: A — Absolute

Gauge pressure is measured relative to atmospheric pressure. Adding the atmospheric pressure, about 1.013 bar, to the gauge reading gives the absolute pressure measured from a perfect vacuum, which is used in gas law calculations.

30. The main purpose of zero gas is calibration of the ____ reading of gas detectors.

A. Zero
B. Span
C. Alarm set-point
D. Full-scale

Answer: A — Zero

Zero gas, normally nitrogen or clean air free of the target gas, is used to set the instrument's zero point. A span gas of known concentration is then used to adjust the upper reading, completing the calibration.

Set 13 — 30 GASCO exit exam questions with answers

1. The temperature at which a liquid starts boiling is called the ____.

A. Boiling temperature
B. Critical temperature
C. Absolute temperature
D. Freezing temperature

Answer: A — Boiling temperature

The boiling temperature is the temperature at which the saturated vapour pressure of a liquid equals the surrounding pressure, so vapour forms throughout the liquid. For liquefied gases it is quoted at atmospheric pressure, such as -162°C for methane.

2. Latent heat is termed latent heat of vaporization in the case of ____.

A. Boiling
B. Melting
C. Freezing
D. Sublimation

Answer: A — Boiling

Latent heat of vaporization is the heat absorbed when a liquid changes into vapour at constant temperature, as in boiling. Melting and freezing involve latent heat of fusion, while sublimation involves latent heat of sublimation.

3. ____ refers to the strongest concentration of petroleum vapour in air that will burn.

A. Upper explosive limit
B. Lower explosive limit
C. Stronger explosive limit
D. Maximum explosive limit

Answer: A — Upper explosive limit

The upper explosive (flammable) limit is the maximum concentration of hydrocarbon vapour in air that can be ignited. Above it the mixture is too rich to burn; below the lower explosive limit it is too lean.

4. ____ is a process in which a liquid changes into a vapour or gas.

A. Boiling
B. Freezing
C. Condensation
D. Melting

Answer: A — Boiling

Boiling is the change of state from liquid to vapour that occurs throughout the liquid when its vapour pressure equals the surrounding pressure. Condensation is the reverse process, while freezing and melting involve the solid state.

5. A gas at a temperature ____ its critical temperature is called a vapour.

A. Below
B. Above
C. Exactly at
D. Far above

Answer: A — Below

Above the critical temperature a gas cannot be liquefied by pressure alone. Below the critical temperature it is called a vapour because it can be condensed by compression, which is the basis of carrying liquefied gases under pressure or refrigeration.

6. When the nitrogen generator is in "purge mode", the nitrogen produced is ____.

A. Vented continuously to atmosphere
B. Supplied continuously to the cargo area
C. Continuously supplied to the gas burning system
D. Re-circulated continuously within the nitrogen generator

Answer: A — Vented continuously to atmosphere

On start-up, or when the product is off-specification, the nitrogen generator runs in purge mode and the output is vented to atmosphere until the required purity and dew point are reached. Only then is it directed to the buffer tank and consumers.

7. What should an LNG tanker be provided with to change LNG liquid into LNG vapour?

A. Vaporizer
B. Heater
C. Low duty (LD) compressor
D. High duty (HD) compressor

Answer: A — Vaporizer

The LNG vaporizer is a steam-heated heat exchanger that converts liquid LNG into vapour, used for gassing-up, purging and supplementing boil-off for gas burning. Heaters warm vapour that is already gaseous, and compressors only move vapour.

8. Which of the following is NOT a use of the air dryer plant on a gas carrier?

A. Supplying air to ventilate the accommodation
B. Supplying air to pressurize flooded ballast tanks to empty them after grounding
C. Maintaining a non-corrosive atmosphere in tanks left open for long periods
D. Aerating the cargo tanks prior to inspection or maintenance

Answer: A — Supplying air to ventilate the accommodation

The air dryer supplies low dew point dry air to cargo-related spaces, for aerating tanks, keeping tanks and hold spaces dry and emergency ballast tank pressurization. Accommodation is ventilated by its own air-conditioning system with ordinary outside air.

9. What is the typical dew point of the dry air used for aerating cargo tanks?

A. -55°C to -65°C
B. +55°C to +65°C
C. -140°C to -165°C
D. Same as atmospheric air

Answer: A — -55°C to -65°C

Dry air for aeration must have a very low dew point so that no moisture condenses or freezes in cold tanks and insulation. A dew point of around -55°C to -65°C is typical of the dry air produced by the inert gas/dry air generator.

10. What protection is provided for the auxiliary cargo pump against frequent starting and stopping?

A. Only a limited number of starts is allowed in a set period
B. A high discharge pressure alarm
C. An unlimited number of starts is permitted
D. A low suction pressure trip

Answer: A — Only a limited number of starts is allowed in a set period

Submerged electric cargo pump motors heat up with every start because of high starting current. Manufacturers therefore limit the number of starts allowed within a period, and the control system blocks further starts until the motor has cooled.

11. Onboard a membrane LNG tanker, during purging (gassing-up) of cargo tanks with LNG vapour, what is the target value for completing the operation?

A. Methane content above 80% by volume
B. Methane content above 5% by volume
C. Methane content above 21% by volume
D. Methane content above 10% by volume

Answer: A — Methane content above 80% by volume

Gassing-up displaces the inert gas, mainly CO2 and nitrogen, with LNG vapour. It continues until the methane content at the sampling points exceeds about 80% by volume and CO2 is negligible, so that nothing will freeze during cool-down.

12. Onboard an LNG tanker, what option is available if the LD compressor is out of service during gas burning?

A. Gas burning can be continued by "free flow"
B. Gas burning must be stopped
C. Tank pressure must be reduced by venting each cargo tank
D. The steam dump must be manually controlled throughout

Answer: A — Gas burning can be continued by "free flow"

With the LD compressor stopped, boil-off can still flow to the boilers under the cargo tank vapour pressure alone through the heater and gas header, known as free flow. This keeps tank pressure under control without venting to atmosphere.

13. Onboard an LNG carrier, what is the objective of purging (gassing-up) with LNG vapour prior to cool-down?

A. To remove gases such as CO2 that may freeze
B. To initiate cool-down of the cargo tanks prior to loading
C. To clear dust and foreign particles from the tanks
D. To test the cargo tanks' cryogenic properties

Answer: A — To remove gases such as CO2 that may freeze

Inert gas from the generator contains about 15% CO2, which freezes at around -78°C and would block pumps, valves and spray nozzles. Gassing-up with warm LNG vapour displaces the inert gas before the tanks are cooled down to cargo temperature.

14. Onboard an LNG tanker during gas burning, what is the typical temperature range of the gas at the heater outlet to the boilers?

A. +20°C to +30°C
B. -20°C to -30°C
C. -20°C to 0°C
D. -5°C to +5°C

Answer: A — +20°C to +30°C

Boil-off gas leaving the tanks is very cold, so it is heated in the fuel gas heater to about +20°C to +30°C before going to the engine room. This prevents condensation, protects pipework and seals, and gives stable combustion in the boilers.

15. A soda-acid type water extinguisher contains ____ solution in the container.

A. Sodium bicarbonate
B. Sodium carbonate
C. Sodium sulphate
D. Sodium nitrate

Answer: A — Sodium bicarbonate

In a soda-acid extinguisher the body holds sodium bicarbonate solution and a separate bottle holds sulphuric acid. When mixed, the reaction produces CO2 gas, which pressurises the container and expels the water.

16. What is the process of transfer of thermal energy from a hot body to another at a lower temperature called?

A. Heat transfer
B. Evaporation
C. Condensation
D. Sublimation

Answer: A — Heat transfer

Heat transfer is the flow of thermal energy from a body at higher temperature to one at lower temperature, by conduction, convection or radiation. It is the basis of heat ingress into cargo tanks and of boil-off in liquefied gas carriers.

17. According to Gay-Lussac's law, for a fixed mass of ideal gas at constant volume, which relation is true (P = pressure, T = absolute temperature)?

A. P = Constant x T
B. P = Constant + T
C. P = Constant - T
D. P = Constant / T

Answer: A — P = Constant x T

Gay-Lussac's (pressure) law states that at constant volume the pressure of a fixed mass of gas is directly proportional to its absolute temperature, P/T = constant. This explains why tank pressure rises as cargo vapour warms.

18. When a float gauge is not in use, where should the float be?

A. Retrieved and housed
B. Left at whatever level it was
C. Left down floating on the liquid surface
D. Hanging just above the liquid level

Answer: A — Retrieved and housed

A float left on the liquid surface is subject to sloshing and wave action that can damage the tape, float and guide wires. When gauging is complete the float is raised and secured in its housing at the top of the tank.

19. What is the liquid relative density of ethylene at its atmospheric boiling point?

A. 0.57
B. 0.65
C. 0.36
D. 0.85

Answer: A — 0.57

Ethylene boils at about -104°C at atmospheric pressure, where its liquid relative density is about 0.57. This low density, compared with about 0.58 for propane and 0.42 to 0.47 for LNG, affects tank filling and loading calculations.

20. Removal of liquid from the cargo tank may cause a ____ in inter-barrier space pressure, which should be monitored throughout the discharge.

A. Change
B. Leak
C. No effect
D. None of the above

Answer: A — Change

As liquid is discharged the cargo tank pressure and temperature conditions change, and the membrane or barrier deflects, so the pressure in the inter-barrier and insulation spaces changes. It must be monitored and adjusted with nitrogen to keep the correct differential.

21. Methane's boiling point at atmospheric pressure is ____.

A. -259°F / -162°C
B. -360°F / -218°C
C. -159°F / -106°C
D. -44°F / -42°C

Answer: A — -259°F / -162°C

Methane, the main component of LNG, boils at about -162°C (-259°F) at atmospheric pressure. LNG is therefore carried fully refrigerated near this temperature in insulated tanks, with boil-off used as fuel or reliquefied.

22. The boiling temperature of water at atmospheric pressure is ____.

A. +100°C / 212°F
B. -100°C / -148°F
C. +250°C / 482°F
D. 0°C / 32°F

Answer: A — +100°C / 212°F

At standard atmospheric pressure of 1.013 bar, water boils at 100°C, which is 212°F. Water freezes at 0°C (32°F). Boiling point rises with pressure and falls when pressure is reduced.

23. Zero gas, used as a calibration gas for gas detectors, is made of pure ____.

A. hydrogen
B. nitrogen
C. oxygen
D. carbon dioxide

Answer: B — nitrogen

Zero gas is pure nitrogen containing no hydrocarbon or oxygen, so the instrument can be set to read zero. Span gas of known concentration is then used to check the upper end of the scale.

24. After discharging the liquid from a cargo tank, a small quantity remains that is difficult to pump out. This small quantity of liquid is called the ____.

A. liquid trap
B. heel
C. mole
D. ullage

Answer: B — heel

The heel is the liquid deliberately or unavoidably left in the tank after discharge. On LNG carriers it is often retained to keep tanks cold during the ballast voyage, avoiding a full cool-down before the next loading.

25. If icing is not very effective on a soft-tissue injury, the next method to be followed around the injured area is ____.

A. compressing
B. resting
C. massaging
D. heating

Answer: A — compressing

Soft-tissue injuries are treated by the RICE method: Rest, Ice, Compression and Elevation. After ice, a compression bandage around the injured area limits swelling. Massage and heat increase blood flow and swelling and should be avoided initially.

26. Identify the solution used in the container of a soda-acid type water fire extinguisher.

A. Sodium sulphate
B. Sodium bicarbonate
C. Sodium nitrate
D. Calcium chloride

Answer: B — Sodium bicarbonate

The body of a soda-acid extinguisher holds a sodium bicarbonate solution. When the acid bottle is broken, the acid reacts with the bicarbonate to generate carbon dioxide, which pressurises the container and expels the water.

27. If there is a possibility of cargo vapour being drawn into the accommodation, the accommodation ventilation system should be ____.

A. stopped or operated on closed (recirculation) cycle
B. run at maximum fresh-air intake
C. operated with all doors and ports opened
D. left unchanged as accommodation is a safe space

Answer: A — stopped or operated on closed (recirculation) cycle

ISGOTT and the gas tanker safety guides require air intakes to be closed and ventilation stopped or put on recirculation when cargo vapour may reach the accommodation, so that flammable or toxic vapour is not drawn into gas-safe spaces.

28. At the commencement of loading a gas cargo, the loading rate should be ____.

A. slow, until the line-up, tightness and tank conditions are confirmed
B. the maximum rate permitted by the terminal
C. high pressure direct loading to save time
D. varied randomly to test the system

Answer: A — slow, until the line-up, tightness and tank conditions are confirmed

Loading always starts at a reduced rate so that leaks, wrong line-ups, pressure build-up and cooling of lines can be checked before increasing to the agreed full rate. High pressure direct loading at start-up is unsafe.

29. In a typical membrane-type nitrogen generator, the purge valve opens and the delivery valve closes automatically when there is ____.

A. low oxygen content (0.5% volume) and low dew point (-70°C)
B. high oxygen content (5% volume) and low dew point (-60°C)
C. low oxygen content (0.1% volume) and high dew point (-40°C)
D. high oxygen content (3% volume) and high dew point (-55°C)

Answer: D — high oxygen content (3% volume) and high dew point (-55°C)

The nitrogen generator diverts its output to atmosphere through the purge valve when the product goes off-specification, that is when oxygen content and dew point are both too high. Delivery to the buffer tank resumes once purity and dryness return to specification.

30. You are using the displacement method for inerting cargo tanks. If mixing occurs, what will happen to the quantity of inert gas required?

A. No change in the quantity of inert gas required
B. 3 to 5 times more inert gas is required
C. Twice the amount of inert gas is required
D. Half the amount of inert gas is required

Answer: B — 3 to 5 times more inert gas is required

Ideal displacement needs only about one to one and a half tank volumes because the gas layers stay separate. If mixing occurs the process becomes dilution, which typically needs three to five tank volumes of inert gas to reach the required oxygen level.

Set 14 — 30 GASCO exit exam questions with answers

1. On board an LNG tanker during gas burning, what option is available if the volume of boil-off is too great for the boilers to handle?

A. Vent excess boil-off from the cargo tanks through the common vent riser
B. Increase the rate of gas burning beyond the boiler capacity
C. Divert excess boil-off to a separate storage tank
D. Reduce the temperature of the cargo to decrease boil-off volume

Answer: A — Vent excess boil-off from the cargo tanks through the common vent riser

Conventional steam LNG carriers have no reliquefaction or storage for excess boil-off. Pressure is controlled by burning gas, dumping steam, and, as a last resort, venting surplus vapour through the common mast riser after heating it.

2. What instrument is used to measure the dew point of the cargo tank atmosphere during cargo operations?

A. Barometer
B. Anemometer
C. Thermometer
D. Hygrometer

Answer: D — Hygrometer

A dew point meter is a type of hygrometer that measures the moisture content of a gas. Dew point is checked during drying, inerting and aerating to prevent ice and hydrate formation in valves, pumps and gauges.

3. When treating chemical burns, for how long should the affected area be kept under cool running water?

A. 5 minutes
B. 15 minutes
C. 20 minutes
D. 30 minutes

Answer: C — 20 minutes

Current first-aid guidance is to flush chemical burns with cool running water for at least 20 minutes to dilute and remove the chemical and cool the tissue, removing contaminated clothing while flushing, and to seek medical advice.

4. On board an LNG carrier during loading, what will happen when the cargo level in a tank reaches the high-high level setting (about 98.6% by volume)?

A. The loading operation will continue uninterrupted
B. The tank will automatically release excess pressure
C. The tank will start venting excess cargo to maintain safe levels
D. The high-level alarm will sound and the filling valve will close automatically

Answer: D — The high-level alarm will sound and the filling valve will close automatically

IGC Code Chapter 13 requires an overflow control system independent of the gauging system. At the high-high level it gives an alarm and automatically closes the tank filling valve to prevent overfilling the tank.

5. How would you determine whether a cargo pump is working correctly, i.e. pumping at the correct rate?

A. Measure the voltage output of the pump
B. Check the motor amperage load on the switchboard
C. Monitor the temperature of the pump casing
D. Observe the colour of the pump discharge

Answer: B — Check the motor amperage load on the switchboard

For submerged electric cargo pumps the motor current, together with discharge pressure, indicates the pump's operating point on its performance curve. A correct amperage for the given discharge pressure shows the pump is delivering its expected flow rate.

6. What is meant when a liquefied gas cargo is described as flammable?

A. The cargo will not ignite under any circumstances
B. The cargo is safe to handle without any risk of combustion
C. The vapour from the cargo will burn when mixed with air and ignited
D. The cargo does not produce any flammable vapour

Answer: C — The vapour from the cargo will burn when mixed with air and ignited

A flammable cargo gives off vapour that, when mixed with air within its flammable range and exposed to an ignition source, will burn. It is the vapour, not the liquid itself, that burns.

7. What is a typical set point for the insulation space pressure relief valves?

A. 50 mbar below atmospheric pressure
B. 10 mbar above atmospheric pressure
C. 100 mbar above atmospheric pressure
D. 500 mbar below atmospheric pressure

Answer: B — 10 mbar above atmospheric pressure

Insulation and interbarrier spaces are kept at a small positive nitrogen pressure, a few mbar above atmosphere and below the cargo tank pressure. Their relief valves are therefore set only slightly above atmospheric, of the order of 10 mbar, to protect the membrane.

8. What is the Joule-Thomson effect?

A. The change in temperature that accompanies expansion of a gas without production of work or transfer of heat
B. The change in pressure that accompanies compression of a gas without production of work or transfer of heat
C. The change in volume that accompanies contraction of a gas without production of work or transfer of heat
D. The change in entropy that accompanies compression of a gas without production of work or transfer of heat

Answer: A — The change in temperature that accompanies expansion of a gas without production of work or transfer of heat

The Joule-Thomson effect is the temperature change of a real gas expanding through a throttle without doing work or exchanging heat. At ordinary conditions most gases, except hydrogen and helium, cool on expansion, which is used in gas liquefaction.

9. What is Dalton's law of partial pressures?

A. The pressure of a gas mixture is inversely proportional to the total number of gas particles in the mixture
B. The pressure exerted by a mixture of gases is equal to the sum of the separate pressures which each gas would exert if it alone occupied the whole volume
C. The pressure of a gas is directly proportional to the volume it occupies
D. The pressure of a gas is independent of the presence of other gases in the mixture

Answer: B — The pressure exerted by a mixture of gases is equal to the sum of the separate pressures which each gas would exert if it alone occupied the whole volume

Dalton's law states that total pressure equals the sum of the partial pressures of the component gases. It explains, for example, how the vapour pressure of a cargo and the pressure of inert gas combine in a tank atmosphere.

10. What is a submerged centrifugal pump?

A. A type of positive displacement pump
B. A pump installed above the cargo tank
C. A centrifugal cargo pump installed at the bottom of the cargo tank with the motor, impeller and bearings totally submerged in the cargo
D. A pump used exclusively for ballast operations

Answer: C — A centrifugal cargo pump installed at the bottom of the cargo tank with the motor, impeller and bearings totally submerged in the cargo

Submerged motor pumps, common on gas carriers and terminals, sit in the tank bottom with motor, impeller and bearings immersed. The liquefied gas itself cools and lubricates the bearings and motor, and no shaft seal through the tank top is needed.

11. On board a membrane LNG tanker during the ballast voyage, what is the danger if the cargo tank levels are kept above 10% of tank length (in the filling restriction band)?

A. Heavy sloshing may lead to tank damage
B. Improved stability of the vessel
C. Reduced risk of sloshing
D. Increased cargo capacity

Answer: A — Heavy sloshing may lead to tank damage

Membrane tanks have filling restrictions, typically below 10% of tank length or above 70% of tank height. Intermediate levels allow liquid to build up resonant sloshing, whose impact loads can damage the membrane and insulation.

12. Warm LNG vapour is lighter than the inert gas. During gassing-up by the displacement method, what is the best way to supply the warm LNG vapour to the tank?

A. Through the vapour line at the top of the tank, exhausting inert gas through the loading line at the bottom
B. Through the loading line at the tank bottom, exhausting through the top
C. Through the manifold directly to the vent mast
D. By releasing it directly to the atmosphere

Answer: A — Through the vapour line at the top of the tank, exhausting inert gas through the loading line at the bottom

Because warm methane vapour is lighter than inert gas, it is introduced at the tank top and forms a layer that pushes the heavier inert gas out from the bottom through the filling line. Feeding it at the bottom would cause mixing and waste gas.

13. The glass bottle under the cap of a soda-acid type water extinguisher contains ____.

A. sodium bicarbonate solution
B. calcium hydroxide
C. dilute sulphuric acid
D. hydrogen peroxide

Answer: C — dilute sulphuric acid

In a soda-acid extinguisher the small bottle under the cap holds dilute sulphuric acid. Striking the plunger breaks it, the acid mixes with the sodium bicarbonate solution and the carbon dioxide produced expels the water.

14. In the event of various alarms being activated in relation to the cargo systems and the pumps themselves, what is the worst that can happen to the main cargo pumps?

A. Increased speed
B. Manual override
C. They will be automatically stopped
D. Continuous operation

Answer: C — They will be automatically stopped

Main cargo pumps are interlocked with trips such as low tank level, low discharge pressure, overload, low motor current and emergency shutdown. When these alarms or ESD signals are activated, the pumps are stopped automatically to protect the pump and the system.

15. When operating a stripping/spray pump, what should be monitored and adjusted to ensure its most efficient operation as indicated on the performance graph?

A. Temperature of the cargo
B. The pump discharge pressure and pump motor amperes
C. Tank pressure only
D. Colour of the sprayed liquid

Answer: B — The pump discharge pressure and pump motor amperes

The pump's performance curve relates flow, head and motor current. By monitoring discharge pressure and motor amperes and adjusting the discharge valve, the operator keeps the pump at its best efficiency point and avoids cavitation or overload.

16. What is an LNG tanker provided with to manage cargo vapour, especially to ensure the desired flow of boil-off gas from the cargo tanks to the engine room (via the boil-off gas heater) for gas burning?

A. High duty gas compressor
B. A vacuum system
C. A system for direct venting to atmosphere
D. Low duty gas compressor

Answer: D — Low duty gas compressor

The low duty compressor handles the natural boil-off and sends it through the boil-off heater to the engine room for burning in boilers or engines. The high duty compressor is used for returning vapour to shore during loading.

17. Why is the boil-off gas heated prior to venting to atmosphere via the common mast riser?

A. To increase the visibility of the vented gas
B. To avoid venting cold gas, which can create a large white plume and stay at deck level
C. To increase the quantity of gas vented
D. To comply only with noise regulations

Answer: B — To avoid venting cold gas, which can create a large white plume and stay at deck level

Cold methane vapour below about -110°C is heavier than air and condenses atmospheric moisture into a dense white cloud that can fall to deck level. Heating the gas first makes it lighter than air so it disperses safely upward.

18. Why is it necessary to purge all sections of the pipelines and all cargo machinery at the end of the inerting operation (prior to aerating)?

A. To avoid potentially hazardous methane pockets
B. To increase the concentration of methane in the system
C. To create favourable conditions for combustion
D. To save time by skipping the purging process

Answer: A — To avoid potentially hazardous methane pockets

Dead ends in lines, compressors, heaters and vaporisers can trap methane. If not purged with inert gas before air is introduced, these pockets could form flammable mixtures during aeration, so every section must be inerted and tested.

19. When droplets of liquid are carried over into the suction of a compressor and drawn into the compressor, this is called ____.

A. wet suction
B. dry suction
C. moisture-free suction
D. vaporised suction

Answer: A — wet suction

Liquid carry-over into a compressor suction is known as wet suction. Liquid is incompressible and can cause serious mechanical damage, so liquid separators and suction superheat monitoring are used to prevent it.

20. What is the effect of boil-off on the composition of the LNG delivered at the end of the voyage?

A. Higher percentage of nitrogen and methane than in the LNG loaded
B. Unchanged composition compared to the LNG loaded
C. Higher percentage of nitrogen than in the LNG loaded, with less ethane
D. Lower percentage of nitrogen and methane than in the LNG loaded

Answer: D — Lower percentage of nitrogen and methane than in the LNG loaded

Nitrogen and methane are the most volatile components, so they boil off preferentially. This ageing or weathering leaves the delivered LNG richer in ethane, propane and butane, with a slightly higher density and heating value.

21. Failure of one or both main cargo pumps in a tank requires the use of the emergency pump. Which gas is used to purge the pump well before the emergency pump is lowered into it?

A. Oxygen
B. Nitrogen
C. Argon
D. Helium

Answer: B — Nitrogen

Before the emergency pump is lowered, the pump column is purged with nitrogen to remove methane and air, so that no flammable mixture forms when the column is opened. Nitrogen is inert, dry and readily available from the on-board generator.

22. On board an LNG tanker, which pump is normally used to supply LNG to the forcing vaporiser during forced boil-off operation?

A. Spray pump
B. Main cargo pump
C. Diaphragm pump
D. Peristaltic pump

Answer: A — Spray pump

The small stripping/spray pump in the tank supplies LNG to the forcing vaporiser to generate additional fuel gas when natural boil-off is insufficient. It is also used for spraying during cool-down and to keep tanks cold during the ballast voyage.

23. The Heimlich manoeuvre is used for ____.

A. fractures
B. choking
C. burns
D. hypothermia

Answer: B — choking

The Heimlich manoeuvre consists of abdominal thrusts that force air from the lungs to dislodge an object blocking the airway of a conscious choking casualty. It is not used for fractures, burns or hypothermia.

24. What is the minimum requirement for discharge of a fixed carbon dioxide system to fight a fire in the engine room?

A. 50% of the carbon dioxide to be discharged within 2 minutes
B. 100% of the carbon dioxide to be discharged within 10 minutes
C. 75% of the carbon dioxide to be discharged within 5 minutes
D. 85% of the carbon dioxide to be discharged within 2 minutes

Answer: D — 85% of the carbon dioxide to be discharged within 2 minutes

FSS Code Chapter 5 requires the fixed CO2 system for machinery spaces to be able to discharge 85% of the required gas into the space within 2 minutes, giving a rapid inerting effect before the fire can develop.

25. Which statement on heat detectors is correct?

A. Heat detectors are only used in cargo holds
B. Fixed heat detectors are not affected by temperature changes
C. Fixed heat detectors are used in the accommodation and machinery spaces depending on the temperature settings
D. Heat detectors are only used in open deck areas

Answer: C — Fixed heat detectors are used in the accommodation and machinery spaces depending on the temperature settings

Heat detectors operate at a set temperature or rate of rise and are fitted where smoke detectors would give false alarms, such as galleys, laundries and parts of machinery spaces. The FSS Code requires fixed-temperature heat detectors to operate between 54°C and 78°C.

26. Besides carbon dioxide, which other gas can be used as the propellant gas in a dry powder system?

A. Carbon monoxide
B. Oxygen
C. Helium
D. Nitrogen

Answer: D — Nitrogen

Dry powder systems and large extinguishers on gas carriers use inert gas, normally nitrogen, to fluidise and expel the powder. Nitrogen is dry and inert, so it does not cake the powder or support combustion.

27. Which gas can build up in the battery room when batteries are being charged?

A. Nitrogen
B. Oxygen
C. Hydrogen
D. Methane

Answer: C — Hydrogen

Lead-acid batteries release hydrogen and oxygen during charging, especially near full charge. Hydrogen is very light and highly flammable, so battery rooms require good ventilation, explosion-proof fittings and no naked lights.

28. A wide variety of mechanical motions and actions may present hazards to the worker. Which of the following is NOT one of the basic types of hazardous mechanical motion?

A. Static motion
B. Reciprocating motion
C. Oscillating motion
D. Rotating motion

Answer: A — Static motion

Hazardous mechanical motions are rotating, reciprocating, transverse and oscillating movements of machine parts, which can catch, crush or strike a worker. A static part is not a motion at all.

29. When a new vessel is inducted into operations, what will require close monitoring?

A. Navigation equipment
B. Crew accommodation
C. Weather conditions
D. Ship/shore compatibility of loading and unloading procedures

Answer: D — Ship/shore compatibility of loading and unloading procedures

A newly inducted gas carrier must be checked for compatibility with terminals, including manifold arrangement, mooring, emergency shutdown links and cargo transfer procedures. These are monitored closely during the first loading and discharging operations.

30. A radar tank gauge is stamped Ex ia IIC T4. What is the maximum surface temperature allowed?

A. 100°C
B. 150°C
C. 135°C
D. 200°C

Answer: C — 135°C

The temperature class indicates the maximum surface temperature of the equipment: T1 450°C, T2 300°C, T3 200°C, T4 135°C, T5 100°C and T6 85°C. T4 equipment therefore must not exceed 135°C.

Set 15 — 30 GASCO exit exam questions with answers

1. During the inerting operation prior to aerating, why is the inert gas fed via the loading line at the tank bottom and exhausted through the tank top?

A. The heavier inert gas is led to the bottom to displace the lighter methane mixture
B. The lighter inert gas is led to the bottom to displace the heavier methane mixture
C. The inert gas is fed through the tank top to maximise pressure
D. The inert gas is exhausted through the tank bottom to create a vacuum

Answer: A — The heavier inert gas is led to the bottom to displace the lighter methane mixture

Inert gas is heavier than warm methane vapour, so introducing it at the bottom forms a layer that pushes the lighter methane out through the top. This piston-like displacement minimises mixing and the volume of inert gas needed.

2. Which instrument is used to monitor the insulation space during the evacuating process?

A. Barometer
B. Mercury manometer
C. Hydrometer
D. Anemometer

Answer: B — Mercury manometer

When an insulation space is evacuated and refilled with nitrogen, the low absolute pressure is measured with a manometer or vacuum gauge, traditionally a mercury manometer. Barometers, hydrometers and anemometers do not measure space vacuum.

3. What are the two types of insulation systems used on Moss spherical tanks?

A. Inorganic blanket insulation and foam insulation
B. Panel insulation and spiral generation insulation systems
C. Double-hull insulation and vacuum insulation
D. Liquid nitrogen insulation and balsa insulation

Answer: B — Panel insulation and spiral generation insulation systems

Moss spheres are externally insulated with polyurethane foam either in prefabricated panels fitted to the tank or by the spiral generation method, in which foam is applied in a continuous spiral as the sphere rotates.

4. If an LNG sale contract is on free on board (FOB) terms, when does the risk pass from the seller to the buyer?

A. When the goods are delivered to the buyer's facility
B. When the goods pass the ship's rail (are placed on board) at the load port
C. Progressively during the entire voyage
D. At the discharge port

Answer: B — When the goods pass the ship's rail (are placed on board) at the load port

Under FOB terms the seller delivers the goods on board the vessel nominated by the buyer at the load port. Risk passes at that point, traditionally the ship's rail, and the buyer bears freight, insurance and voyage risk thereafter.

5. What is the material of construction of the spherical Moss type cargo tank?

A. Aluminium alloy, about 30 to 200 mm thick
B. 316L stainless steel
C. 9% nickel steel
D. Fibreglass reinforced plastic

Answer: A — Aluminium alloy, about 30 to 200 mm thick

Moss spherical tanks are built of aluminium alloy (typically 5083), which retains its toughness at -163°C. The plate thickness varies from roughly 30 mm to about 200 mm at the equatorial ring where the sphere is supported by the skirt.

6. What is the traditional propulsion system used on board LNG carriers?

A. Steam turbines
B. Internal combustion engines
C. Wind turbines
D. Electric motors

Answer: A — Steam turbines

Traditional LNG carriers use steam turbine propulsion with dual-fuel boilers that can burn the cargo boil-off gas and fuel oil. Newer ships increasingly use dual-fuel diesel-electric or slow-speed gas engines.

7. What is burnt in the dual-fuel boilers of LNG ships with steam turbine propulsion?

A. Boil-off gas and heavy fuel oil
B. Diesel fuel only
C. Compressed natural gas only
D. Water

Answer: A — Boil-off gas and heavy fuel oil

Dual-fuel boilers on steam LNG carriers burn natural boil-off and forced boil-off gas, together with or instead of heavy fuel oil. This uses the cargo boil-off as fuel and avoids venting it.

8. The temperature of a gas or vapour decreases when it is ____.

A. compressed
B. heated
C. expanded
D. kept stable

Answer: C — expanded

When a gas expands, its molecules do work against their surroundings or internal forces and its temperature falls. This principle is used in refrigeration and reliquefaction cycles; compression has the opposite effect and raises the temperature.

9. Why is the Moss LNG cargo tank fitted with external insulation?

A. To increase the weight of the tank
B. To reduce boil-off
C. To enhance heat transfer
D. To prevent external corrosion

Answer: B — To reduce boil-off

External polyurethane foam insulation on Moss spheres limits heat ingress from the hold and surroundings into the -163°C cargo. Reducing heat ingress keeps boil-off to a small daily percentage of the cargo and protects the hull steel from low temperatures.

10. Pressure measured above atmospheric pressure (with atmospheric taken as zero) is called ____ pressure.

A. absolute
B. differential
C. gauge
D. atmospheric

Answer: C — gauge

Gauge pressure is measured relative to atmospheric pressure, which is taken as zero. Absolute pressure equals gauge pressure plus atmospheric pressure, about 1.013 bar at sea level.

11. What type of alarm can be expected when an air dryer plant is starting up, as air is initially drawn across the cooling coil and through the dryer tank?

A. High humidity (high dew point) alarm
B. Low temperature alarm
C. Low pressure alarm
D. High pressure alarm

Answer: A — High humidity (high dew point) alarm

At start-up the desiccant and cooling coil have not yet brought the outlet air to specification, so the dew point of the delivered air is high. A high humidity or high dew point alarm is normal until the dryer settles down.

12. How does bringing down the dew point of the cargo tank atmosphere help?

A. It increases the risk of ice formation
B. It has no impact on the system
C. It reduces the efficiency of the cargo tank
D. It prevents ice and hydrate formation in valves and pumps

Answer: D — It prevents ice and hydrate formation in valves and pumps

Drying the tank atmosphere to a low dew point before cool-down removes moisture that would otherwise freeze or form hydrates at cargo temperatures, blocking valves, pumps, gauges and lines.

13. Which of these gases would not require a stenching agent to be added?

A. Methane
B. Hydrogen
C. Ammonia
D. Ethane

Answer: C — Ammonia

Ammonia has a strong, pungent natural odour detectable at very low concentrations, so no stenching agent is needed. Odourless gases such as methane, hydrogen and ethane need an odorant to make leaks detectable by smell.

14. You have finished discharging a cargo of butane and wish to clear the lines to shore of liquid. How would you do this?

A. Use water to flush the lines
B. Vent the lines to the atmosphere
C. Inject air into the lines
D. Pressurise the lines with hot gas from the reliquefaction plant compressor

Answer: D — Pressurise the lines with hot gas from the reliquefaction plant compressor

After discharge, liquid in the shore line is blown ashore using hot vapour from the cargo compressor. This avoids introducing air or water and does not vent cargo to atmosphere.

15. How would you identify roll-over in a full or partly full cargo tank?

A. Sudden drop in temperature
B. Gradual decrease in pressure
C. Stable pressure and temperature
D. Rapid rise in tank pressure

Answer: D — Rapid rise in tank pressure

Roll-over occurs when stratified layers of different density suddenly mix. The superheated lower layer releases a large volume of vapour, causing a rapid rise in tank pressure that may lift the relief valves.

16. Where would you look to find the properties and hazards of a gas carried on your ship?

A. The cargo data sheet (e.g. the ICS Tanker Safety Guide - Liquefied Gas data sheets)
B. The ship's logbook
C. ISGOTT
D. The SOLAS Convention

Answer: A — The cargo data sheet (e.g. the ICS Tanker Safety Guide - Liquefied Gas data sheets)

Cargo data sheets, such as those in the ICS Tanker Safety Guide (Liquefied Gas) or the SDS, give physical and chemical properties, health hazards, reactivity, firefighting and first aid for each cargo. They must be available on board before loading.

17. There are various IMO gas carrier codes. What determines which code a ship must comply with?

A. The flag state of the ship
B. The year of construction (keel laying date)
C. The type of cargo carried
D. The length of the ship

Answer: B — The year of construction (keel laying date)

Gas carriers comply with the code in force when they were built: the Code for Existing Ships for ships before 1977, the GC Code for 1977 to 1986, and the IGC Code for ships with keel laid on or after 1 July 1986, with later amendments by date.

18. Colourless and odourless gases are stenched to assist in their ____.

A. combustion
B. detection
C. storage
D. containment

Answer: B — detection

A stenching agent such as ethyl mercaptan is added to odourless gases so that leaks can be detected by smell well below the lower flammable limit, giving early warning of a hazardous release.

19. What type of cargo would you normally carry in a ship fitted with independent type B tanks?

A. LNG
B. Crude oil
C. Chemicals
D. Dry bulk cargo

Answer: A — LNG

Independent type B tanks, such as Moss spheres and SPB prismatic tanks, are designed by detailed stress analysis and permit a partial secondary barrier. They are mainly used for LNG, although SPB tanks also carry LPG.

20. One of the parameters to be considered in the design of tanks for refrigerated gas cargoes is ____ stress.

A. mechanical
B. shear
C. thermal
D. tensile

Answer: C — thermal

Refrigerated tanks undergo large temperature changes between ambient and cargo temperature. The resulting contraction and expansion produce thermal stresses, so materials, supports and cool-down rates are designed to control them.

21. A cargo tank has been gas-freed from LNG and you wish to inspect it. From where would you take samples to test for hydrocarbons?

A. Only from the top
B. Only from the bottom
C. Only from the middle section
D. From the top, the bottom and levels in between

Answer: D — From the top, the bottom and levels in between

Gases may stratify and pockets can remain in corners or low spots, so the atmosphere must be sampled at several levels from top to bottom. Only when all readings are satisfactory can the tank be considered safe for entry.

22. Why is glycol added to the cooling water system of a reliquefaction plant?

A. To stop the water freezing
B. To enhance heat transfer
C. To improve water quality
D. To increase the system pressure

Answer: A — To stop the water freezing

The cooling medium in reliquefaction and cargo heat exchangers can be exposed to very low temperatures. Adding glycol lowers the freezing point of the water so it does not freeze and damage the exchangers or block the circuit.

23. A ____ management system complying with the ISM Code must be in place on all gas carriers of 500 GT and upwards.

A. security
B. safety
C. quality
D. environmental

Answer: B — safety

SOLAS Chapter IX makes the ISM Code mandatory, requiring a Safety Management System for gas carriers and other cargo ships of 500 GT and upwards. The company and ship receive a DOC and SMC after audit.

24. Which of these would you not use on a liquefied gas pool fire?

A. Dry chemical powder
B. High-expansion foam
C. Water jet directly on the pool
D. Isolation of the source of gas

Answer: C — Water jet directly on the pool

Applying water directly onto a liquefied gas pool adds heat and greatly increases the vaporisation rate, intensifying the fire. Dry powder extinguishes the flames, high-expansion foam reduces radiation and vapour, and water spray is used only to cool surroundings.

25. Which of these cargoes would not need total segregation when carried in separate tanks on the same ship?

A. Ammonia and acetaldehyde
B. Ammonia and chlorine
C. Ethylene oxide and ammonia
D. Propane and butane

Answer: D — Propane and butane

Propane and butane are compatible hydrocarbons and are often carried and even mixed as LPG. Reactive pairs such as ammonia with chlorine or acetaldehyde require separate piping and vent systems to prevent dangerous reactions.

26. If the containment pressure of LPG increases, its boiling point will ____.

A. increase
B. remain constant
C. decrease
D. fluctuate

Answer: A — increase

The boiling point of a liquid rises with the pressure above it. This is why LPG can be carried as a liquid at ambient temperature in fully pressurised tanks, and why lowering tank pressure lowers the cargo temperature.

27. A centrifugal pump should always be started against a closed or partially open discharge valve. What is the reason for this?

A. To maximise the pump motor load
B. To maintain constant flow
C. To prevent cavitation in the pump
D. To minimise the pump motor starting load

Answer: D — To minimise the pump motor starting load

Power absorbed by a centrifugal pump rises with flow and is lowest at shut-off. Starting with the discharge valve closed or slightly open limits the starting current and motor load, after which the valve is opened gradually.

28. Which international bodies provide regulatory standards for electrical equipment in hazardous areas?

A. IEEE (Institute of Electrical and Electronics Engineers)
B. IEC (International Electrotechnical Commission) and CENELEC (European Committee for Electrotechnical Standardisation)
C. ISO (International Organization for Standardization)
D. NEMA (National Electrical Manufacturers Association)

Answer: B — IEC (International Electrotechnical Commission) and CENELEC (European Committee for Electrotechnical Standardisation)

The IEC 60079 series sets international standards for explosion-protected electrical equipment, and CENELEC issues the corresponding European norms. The IGC Code refers to IEC standards for electrical installations in gas-dangerous areas.

29. What happens when heat is transferred to the liquid cargo (LNG) during cargo operations or during a voyage?

A. It generates boil-off from the cargo
B. It reduces the temperature of the liquid cargo
C. It has no effect on the liquid cargo
D. It solidifies the liquid cargo

Answer: A — It generates boil-off from the cargo

LNG is carried at its boiling point at near-atmospheric pressure. Any heat that leaks in through the insulation or from pumps does not raise the temperature but evaporates part of the liquid, producing boil-off gas.

30. The water spray system on a gas carrier must have the capacity to cover the protected areas with at least ____ on horizontal surfaces and ____ on vertical surfaces.

A. 5 litres/m²/minute and 2 litres/m²/minute
B. 8 litres/m²/minute and 6 litres/m²/minute
C. 10 litres/m²/minute and 4 litres/m²/minute
D. 12 litres/m²/minute and 3 litres/m²/minute

Answer: C — 10 litres/m²/minute and 4 litres/m²/minute

IGC Code Chapter 11 requires the water spray system to cover the protected areas uniformly with at least 10 litres/m² per minute on horizontal projected surfaces and 4 litres/m² per minute on vertical surfaces.

Set 16 — 30 GASCO exit exam questions with answers

1. LNG is always stored on board ships in insulated tanks at a(n) ____.

A. room temperature
B. extremely low temperature
C. high pressure
D. moderate temperature

Answer: B — extremely low temperature

LNG is carried fully refrigerated at about -163°C, its boiling point at near-atmospheric pressure. Insulated tanks limit heat ingress so that only a small amount of boil-off is produced.

2. What must be eliminated to prevent accidents?

A. Safe conditions
B. Proper equipment
C. Unsafe actions
D. Effective safety measures

Answer: C — Unsafe actions

Accidents result from unsafe acts and unsafe conditions. Eliminating unsafe actions through training, supervision, procedures and a good safety culture, together with removing unsafe conditions, is the basis of accident prevention.

3. The ____ of a liquid is defined as the lowest temperature at which the liquid gives off sufficient vapour to form a flammable mixture with air.

A. autoignition temperature
B. boiling point
C. freezing point
D. flash point

Answer: D — flash point

Flash point is the lowest temperature at which a liquid produces enough vapour to form a flammable mixture with air near its surface that can be ignited by a flame. Autoignition temperature is the temperature at which vapour ignites without an external source.

4. LNG vapour can ignite or explode when mixed with air within its flammable range of about ____.

A. 25-30% gas by volume
B. 0-5% gas by volume
C. 5-15% gas by volume
D. 30-50% gas by volume

Answer: C — 5-15% gas by volume

Methane, the main component of LNG, has a lower flammable limit of about 5% and an upper flammable limit of about 15% by volume in air. Outside this range the mixture is too lean or too rich to burn.

5. What is the oxygen target value for completion of the cargo tank aeration operation?

A. About 21% by volume
B. 15% by volume
C. 25% by volume
D. 30% by volume

Answer: A — About 21% by volume

Aeration is continued until the tank atmosphere is essentially fresh air, with oxygen at about 21% by volume (at least 20.8% for entry under enclosed space procedures), hydrocarbons and toxic gases absent, before tanks are opened for entry.

6. Each cargo tank is fitted with which two types of relief valves?

A. Temperature relief valves and pressure relief valves
B. Pressure relief valves and vacuum relief valves
C. Inert gas relief valves and vacuum relief valves
D. Temperature relief valves and inert gas relief valves

Answer: B — Pressure relief valves and vacuum relief valves

Cargo tanks are protected against overpressure by pressure relief valves required by IGC Code Chapter 8, and against excessive vacuum by vacuum relief valves or vacuum protection, so the tank structure is never subjected to pressures outside its design range.

7. On board an LNG carrier at sea, what is the status of the DCS (distributed control system) cargo console?

A. It is only activated during engine maintenance
B. It is used to monitor cargo tank conditions continuously
C. It is disconnected from the cargo system
D. It is used exclusively for crew communication

Answer: B — It is used to monitor cargo tank conditions continuously

At sea the cargo console of the DCS remains in service to monitor tank pressures, temperatures, levels, insulation space conditions, gas detection and boil-off handling continuously, raising alarms if any parameter goes out of range.

8. Why should all cargo tanks be connected to a common vapour header?

A. To isolate each cargo tank
B. To maintain independent pressure control for each tank
C. To allow vapour sharing between tanks and common pressure control
D. To prevent any vapour leaving the tanks

Answer: C — To allow vapour sharing between tanks and common pressure control

Connecting all tanks to a common vapour header lets boil-off from every tank be collected for the compressors and engine room, and keeps pressures equalised so tank pressure can be controlled as one system.

9. In a Moss type LNG cargo tank, where are the pumps, pipework and cabling secured?

A. On the exterior of the cargo tank
B. At the bottom of the cargo tank only
C. In the tubular pipe tower inside the cargo tank
D. Suspended from cables at the top of the cargo tank

Answer: C — In the tubular pipe tower inside the cargo tank

Moss spheres have a vertical tubular pipe tower running from the tank dome to the bottom. It supports the cargo pumps, filling and discharge pipes, gauging and cabling, and provides access for inspection.

10. When the seller and buyer agree to free on board (FOB) terms, what does the buyer pay?

A. Only for the goods
B. Freight, insurance, unloading costs and onward transportation
C. Only the loading costs
D. The seller's expenses

Answer: B — Freight, insurance, unloading costs and onward transportation

Under FOB terms the seller bears costs until the goods are on board at the load port. The buyer charters or nominates the vessel and pays freight, marine insurance, discharge and onward transport costs.

11. An inhibitor is a substance used to prevent or retard cargo deterioration or a potentially hazardous ____.

A. deterioration-promoting action
B. increase in reactivity
C. self-reaction such as polymerisation
D. dilution of the cargo

Answer: C — self-reaction such as polymerisation

Inhibitors are added to cargoes such as butadiene, vinyl chloride and styrene to prevent self-reaction, mainly polymerisation, which can generate heat and pressure. An inhibitor certificate must be provided by the shipper under the IGC and IBC Codes.

12. What is the critical temperature of propane?

A. -96.8°C
B. 96.8°F
C. 96.8°C
D. 968 K

Answer: C — 96.8°C

Propane's critical temperature is about 96.8°C, above which it cannot be liquefied by pressure alone. Because this is well above ambient, propane can be carried as a liquid in pressurised tanks at ambient temperature.

13. The gas code requires gas carriers to have a fixed gas detection system with ____ alarm.

A. only visual
B. audible and visual
C. only audible
D. no

Answer: B — audible and visual

IGC Code Chapter 13 requires permanently installed gas detection with audible and visual alarms on the navigation bridge, in the cargo control position and at the gas detector readout location.

14. For cargo classification, the flash point of a liquid is usually measured by which method?

A. Closed cup method
B. Open cup method
C. Reid method
D. Hydrometer method

Answer: A — Closed cup method

Flash points quoted for cargo classification under MARPOL, the IBC Code and ISGOTT are normally determined by a closed cup test, which gives lower, more conservative values than open cup tests. The Reid method measures vapour pressure, not flash point.

15. Which inhibitors are highly toxic, so that great care must be taken in handling inhibitors and inhibited cargoes?

A. Distilled water
B. Carbon dioxide
C. Hydroquinone and tertiary butyl catechol (TBC)
D. Nitrogen gas

Answer: C — Hydroquinone and tertiary butyl catechol (TBC)

Common polymerisation inhibitors such as hydroquinone and tertiary butyl catechol are toxic by skin contact and inhalation. Personnel handling inhibitors or inhibited cargoes must use appropriate PPE and follow the cargo data sheet.

16. What is the critical parameter to be observed for the supply of air to cargo tanks for the aerating operation?

A. Ambient temperature of the surrounding area
B. Dew point of the dry air supply
C. Colour of the air supply
D. Volume of air supplied

Answer: B — Dew point of the dry air supply

Aeration uses dry air so that moisture is not introduced into the cold tank and insulation. The dew point of the dry air must be monitored to prevent condensation and corrosion in tanks and pipework.

17. If you wish to enter or leave a space through an airlock, what does it mean if the warning light outside the airlock is lit?

A. The airlock is ready for entry and you can proceed without any restrictions
B. The light indicates a malfunction, but it is safe to enter
C. The airlock's other door is open and you must not try to enter until the light goes out
D. The warning light is not relevant to the airlock operation

Answer: C — The airlock's other door is open and you must not try to enter until the light goes out

IGC Code airlocks have two self-closing gastight doors that must not be open at the same time. A warning light or alarm shows that the other door is open, so you must wait until it is closed before opening your door.

18. If someone is injured by a spillage of liquefied gas, where would you look initially for information on how to treat the injury?

A. Ship's maintenance manual
B. Crew members' personal notes
C. ICS cargo data sheet
D. Local maritime regulations

Answer: C — ICS cargo data sheet

The cargo data sheet (ICS Tanker Safety Guide - Liquefied Gas data sheet or the cargo MSDS) gives the health hazards, first-aid treatment and protective measures for each liquefied gas, so it is the first reference for treating cargo-related injuries.

19. What is the usual method of cargo tank pressure control used on LNG carriers?

A. Releasing the boil-off gas directly into the atmosphere
B. Burning the boil-off in the ship's boilers or engines
C. Converting the boil-off gas into electricity by fuel cells
D. Storing the boil-off gas in separate tanks for later use

Answer: B — Burning the boil-off in the ship's boilers or engines

On conventional LNG carriers the natural boil-off is sent by low-duty compressors to the boilers or dual-fuel engines as fuel, which keeps tank pressure under control. IGC Code chapter 7 and chapter 16 allow use of cargo boil-off as fuel; venting to atmosphere is not a normal pressure-control method.

20. The location of electrical equipment is often classified by zones. What does Zone 1 mean?

A. No risk of flammable materials; completely safe
B. A flammable atmosphere is not likely in normal operation and, if it occurs, exists only for a short time
C. An explosive gas atmosphere is likely to occur in normal operation
D. Zone 1 is not a relevant classification for electrical equipment

Answer: C — An explosive gas atmosphere is likely to occur in normal operation

Under IEC 60079-10 hazardous-area classification, Zone 0 has an explosive atmosphere present continuously, Zone 1 is where an explosive gas atmosphere is likely to occur in normal operation, and Zone 2 is where it is unlikely and only for short periods.

21. Which dangerous gases are emitted from a sewage tank?

A. Oxygen and nitrogen
B. Methane and hydrogen sulphide
C. Carbon dioxide and helium
D. Hydrogen and nitrogen dioxide

Answer: B — Methane and hydrogen sulphide

Anaerobic decomposition of sewage produces methane, which is flammable, and hydrogen sulphide, which is highly toxic. Sewage tanks must therefore be treated as enclosed spaces with gas testing before entry.

22. In first aid, RICE stands for?

A. Rest, ice, compression and elevation
B. Rapid infiltration and convection elevation
C. Respiratory infection control effort
D. Rotational inertia conversion element

Answer: A — Rest, ice, compression and elevation

RICE - rest, ice, compression and elevation - is the standard first-aid treatment for sprains, strains and soft-tissue injuries, reducing swelling, pain and further damage in the first 24 to 48 hours.

23. How many portable multi-gas detectors should be carried on board a gas carrier?

A. At least two sets with methane gas detection capability
B. Only one set with methane gas detection capability
C. At least three sets with methane gas detection capability
D. No portable multi-gas detectors are required on board

Answer: A — At least two sets with methane gas detection capability

The IGC Code requires every gas carrier to carry at least two sets of portable gas detection equipment suitable for the cargoes carried, plus an oxygen analyser, so that a spare is always available if one instrument fails.

24. Which machinery is used for the initial pressurisation of insulation spaces?

A. Vacuum pump
B. Air compressor
C. Steam turbine
D. Nitrogen generator

Answer: D — Nitrogen generator

Hold and insulation spaces around cargo tanks, especially membrane interbarrier spaces, are filled and pressurised with dry nitrogen from the nitrogen generator, keeping them inert and dry and allowing leaks to be detected.

25. Which is the correct statement about monitoring typical HSE performance indicators?

A. HSE performance monitoring uses only LTIF and disregards TRCF
B. Monitoring HSE performance indicators relies solely on financial metrics
C. Only TRCF is essential for monitoring HSE performance
D. Both LTIF (Lost Time Injury Frequency) and TRCF (Total Recordable Case Frequency) are monitored

Answer: D — Both LTIF (Lost Time Injury Frequency) and TRCF (Total Recordable Case Frequency) are monitored

Lost Time Injury Frequency and Total Recordable Case Frequency are the standard lagging HSE indicators used by shipping companies and oil majors (for example under TMSA), so both are tracked together to monitor safety performance.

26. According to Charles's law for an ideal gas at constant pressure, which statement is correct?

A. V = constant x T
B. V = T + constant
C. V = constant / T
D. V = constant x T^2

Answer: A — V = constant x T

Charles's law states that at constant pressure the volume of a fixed mass of ideal gas is directly proportional to its absolute temperature, so V/T is constant, giving V = k x T.

27. What is the priority order of a company's on-board policies and procedures?

A. Profit maximisation at any cost
B. Minimising maintenance costs above all else
C. Ignoring safety protocols for expedited operations
D. Safety of the crew, safe operation of the vessel, protection of the environment

Answer: D — Safety of the crew, safe operation of the vessel, protection of the environment

Under the ISM Code the company safety and environmental protection policy puts safety of life first, then safe operation of the ship and protection of the environment, followed by protection of property and commercial interests.

28. Why is inert gas from a generator often preferred over nitrogen for inerting cargo tanks on gas carriers?

A. Inert gas is chemically more effective than nitrogen
B. Nitrogen is always preferred and used more
C. Nitrogen cannot be generated on board
D. Nitrogen is more expensive and the quantity required is large

Answer: D — Nitrogen is more expensive and the quantity required is large

Inerting full cargo tanks needs very large volumes of gas. Shore-supplied or membrane-generated nitrogen is costly and slow at that volume, so a combustion-type inert gas generator is normally used, with nitrogen kept for cargoes like ammonia and for hold spaces.

29. A spark of sufficient temperature and energy to ignite a flammable gas is called?

A. Incendive spark
B. Ignition spark
C. Catalyst spark
D. Incendiary spark

Answer: A — Incendive spark

ISGOTT defines an incendive spark as a spark of sufficient temperature and energy to ignite a flammable gas or vapour mixture. Static discharges and electrical faults can produce incendive sparks in hazardous areas.

30. The purpose of cooling down cargo tanks and piping prior to loading is to prevent undue ____.

A. Overcooling
B. Vapourisation
C. Thermal stresses
D. Pressurisation

Answer: C — Thermal stresses

Cooling down tanks and pipelines slowly with cargo spray before loading reduces the temperature difference between the steel and the cold liquid, preventing undue thermal stresses in the containment system, as described in the IGC Code and SIGTTO guidance.

Set 17 — 30 GASCO exit exam questions with answers

1. Type 3G ships are permitted to carry only ____ and ____ cargoes.

A. Hazardous and explosive
B. Nitrogen and refrigerant gas
C. Radioactive and flammable
D. Pressurised and corrosive

Answer: B — Nitrogen and refrigerant gas

In chapter 19 of the IGC Code, products such as nitrogen and refrigerant gases are assigned ship type 3G, the least stringent type, because they are non-flammable and of low toxicity.

2. A liquid with an absolute vapour pressure exceeding 2.8 bar (kg/cm2) at 37.8 degrees Celsius, and certain other substances specified in the Code, is known as?

A. Liquefied gas
B. Volatile water
C. High-pressure oil
D. Non-flammable solvent

Answer: A — Liquefied gas

The IGC Code defines liquefied gases as liquids having a vapour pressure exceeding 2.8 bar absolute at 37.8°C, together with certain other substances listed in chapter 19 of the Code.

3. Vapour produced above a cargo liquid surface due to evaporation caused by heat ingress is known as?

A. Condensation
B. Precipitation
C. Boil-off
D. Sublimation

Answer: C — Boil-off

Boil-off is vapour generated when heat leaks through the tank insulation into a refrigerated cargo, causing it to evaporate. It must be handled by reliquefaction, use as fuel or a gas combustion unit to control tank pressure.

4. A centrifugal pump sets the liquid into motion by means of ____ and ____ force.

A. Gravitational and magnetic
B. Kinetic and centrifugal
C. Thermal and frictional
D. Electromagnetic and pneumatic

Answer: B — Kinetic and centrifugal

The rotating impeller of a centrifugal pump gives the liquid kinetic energy and throws it outward by centrifugal force; the volute or diffuser then converts this velocity into pressure head.

5. The cargo compressor room is maintained at ____ air pressure.

A. Negative
B. Positive
C. Neutral
D. Vacuum

Answer: A — Negative

The compressor room is a gas-dangerous space, so its mechanical ventilation extracts air and keeps it at negative pressure relative to adjacent spaces. Any leakage flows inward, while the electric motor room is kept at positive pressure.

6. If the cargo is fully ____ at -163 degrees Celsius, the cargo tanks are made from aluminium or nickel steel.

A. Heated
B. Pressurised
C. Insulated
D. Refrigerated

Answer: D — Refrigerated

LNG is carried fully refrigerated at about -163°C at near atmospheric pressure. Materials in contact with it must keep their toughness at that temperature, so the IGC Code requires aluminium alloys, 9% nickel steel, austenitic stainless steel or invar.

7. The two main types of compressors used on gas carriers are the ____ and ____ types.

A. Rotary and reciprocating
B. Centrifugal and pneumatic
C. Linear and turbo
D. Hydraulic and diaphragm

Answer: A — Rotary and reciprocating

Cargo compressors on LPG carriers are mainly reciprocating (oil-free piston) machines or rotary screw compressors. Both are positive-displacement types used for reliquefaction, vapour return and gassing-up duties.

8. The purpose of gas freeing is to replace residues of inert gas and cargo vapour with:

A. Liquid nitrogen
B. Oxygen
C. Dry air
D. Carbon monoxide

Answer: C — Dry air

Gas freeing (aeration) replaces inert gas and cargo vapour in the tank with dry air until the atmosphere holds 21% oxygen and no harmful vapour. Dry air is used so that moisture and ice do not form.

9. What is the vapour relative density (air = 1) of methane?

A. 2.07
B. 1.55
C. 0.42
D. 0.55

Answer: D — 0.55

Methane has a molecular mass of 16 against about 29 for air, giving a vapour relative density of about 0.55, so methane vapour is lighter than air. The value 0.42 is the relative density of liquid methane.

10. Which types of valves are commonly used on gas tankers?

A. Piston valves, diaphragm valves, needle valves, check valves
B. Ball valves, globe valves, gate valves, butterfly valves
C. Plug valves, spool valves, pinch valves, pressure relief valves
D. Slide valves, control valves, solenoid valves, safety valves

Answer: B — Ball valves, globe valves, gate valves, butterfly valves

Cargo systems on gas carriers mainly use ball, globe, gate and butterfly valves, made of materials suited to low temperatures and often with extended bonnets to keep the gland seals away from the cold cargo.

11. Which type of ship is most suitable for carrying smaller cargoes of LPG and chemical gases on short-sea and near-sea routes?

A. Fully pressurised ships
B. Fully refrigerated ships
C. Membrane LNG carriers
D. Large ethylene carriers

Answer: A — Fully pressurised ships

Fully pressurised ships have small Type C pressure vessels and carry LPG and chemical gases at ambient temperature without reliquefaction. They are simple and cheap to run, so they suit small parcels on short coastal routes.

12. An enclosed space in the cargo area, external to a cargo containment system, other than a hold space, ballast space, fuel oil tank, cargo pump or compressor room, or any space in normal use by personnel, is called?

A. Habitable zone
B. Restricted area
C. Confined space
D. Void space

Answer: D — Void space

This is the IGC Code definition of a void space: an enclosed space in the cargo area outside the cargo containment system that is not a hold, ballast, fuel, cargo pump or compressor room or a space normally used by personnel.

13. On a fully refrigerated gas tanker carrying liquid butane, how is the tank pressure controlled?

A. By the reliquefaction plant
B. By adjusting the ship's draft
C. By manual manipulation of the tank valves
D. By the cargo pump discharge pressure

Answer: A — By the reliquefaction plant

On fully refrigerated LPG ships the boil-off vapour is drawn off by the cargo compressors, condensed in the reliquefaction plant and returned to the tank, keeping cargo temperature and tank pressure within the design limits required by IGC chapter 7.

14. The temperature at which the heat from combustion of burning vapours is capable of producing sufficient vapour for combustion to continue is called?

A. Fire point
B. Ignition temperature
C. Flash point
D. Auto-ignition temperature

Answer: A — Fire point

At the flash point vapour ignites only momentarily. At the fire point, slightly higher, the liquid gives off vapour fast enough to keep the flame burning once it has been ignited.

15. The pressure at which a substance exists in the liquid state at its critical temperature (the saturation pressure at the critical temperature) is called?

A. Saturation pressure
B. Critical pressure
C. Vapour pressure
D. Triple point pressure

Answer: B — Critical pressure

Critical pressure is the saturation vapour pressure at the critical temperature. Above the critical temperature a gas cannot be liquefied by pressure alone, however high that pressure is.

16. The gas codes call for sampling intervals from any one space generally not exceeding how many minutes?

A. 40 minutes
B. 35 minutes
C. 38 minutes
D. 30 minutes

Answer: D — 30 minutes

For sequential sampling fixed gas detection systems, the IGC Code requires that each sampling point be sampled at intervals not exceeding 30 minutes, so a leak in any monitored space is detected promptly.

17. Inhibiting the flame is the most ____ way to extinguish a free-burning liquefied gas fire.

A. Inefficient
B. Unreliable
C. Effective
D. Expensive

Answer: C — Effective

Dry chemical powder interrupts the combustion chain reaction, inhibiting the flame. For free-burning liquefied gas fires this is the most effective method of extinguishment, which is why the IGC Code requires a fixed dry powder system on deck.

18. Which law states that equal volumes of different gases at the same pressure and temperature contain the same number of molecules?

A. Boyle's law
B. Avogadro's law
C. Charles's law
D. Gay-Lussac's law

Answer: B — Avogadro's law

Avogadro's law states that equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules. It is why one mole of any ideal gas takes up about 22.4 litres at STP.

19. A ship whose gas cargo is listed in chapter 19 of the IGC Code and has very severe safety and environmental hazards, requiring maximum preventive measures to preclude escape of the cargo, is called which type of ship?

A. Type 2G
B. Type 3G
C. Type 1G
D. Type 4G

Answer: C — Type 1G

The IGC Code defines a Type 1G ship as a gas carrier intended for products needing maximum preventive measures to prevent their escape, such as chlorine. Type 2G and 3G ships are for progressively less hazardous products.

20. What is the purpose of heat exchangers in a gas carrier's cargo handling system?

A. As air and inert gas driers, lubricating oil coolers, liquid cargo heaters, vaporisers, and condensers and intercoolers in the reliquefaction plant
B. Compression of inert gas
C. Generation of electricity
D. Cooling of accommodation spaces

Answer: A — As air and inert gas driers, lubricating oil coolers, liquid cargo heaters, vaporisers, and condensers and intercoolers in the reliquefaction plant

Heat exchangers are used across the cargo plant: driers for air and inert gas, oil coolers, cargo heaters and vaporisers for discharge and gassing up, and condensers and intercoolers in the reliquefaction cycle.

21. Equipment incapable of releasing sufficient electrical or thermal energy to ignite a specific hazardous atmospheric mixture in its most easily ignited concentration is known as?

A. Flameproof
B. Intrinsically safe
C. Non-incendive
D. Explosion proof

Answer: B — Intrinsically safe

Intrinsically safe equipment limits electrical and thermal energy so that, in normal use or under specified faults, it cannot ignite the gas mixture. Flameproof or explosion-proof equipment instead contains an internal explosion within its enclosure.

22. A catalytic explosimeter should not be used in a/an:

A. Oxygen-enriched atmosphere
B. Hydrogen atmosphere
C. Inerted atmosphere
D. Well-ventilated area

Answer: C — Inerted atmosphere

A catalytic filament explosimeter needs oxygen to burn the sample gas on its filament. In an inerted or oxygen-deficient atmosphere it gives false low readings, so hydrocarbon content in inerted tanks must be measured with an infrared or refractometer-type instrument.

23. Which areas does the water spray system cover on gas carriers?

A. Tank domes, cargo deck, manifolds, deck houses and superstructure boundaries facing the cargo area
B. Engine room
C. Accommodation areas
D. Cargo holds

Answer: A — Tank domes, cargo deck, manifolds, deck houses and superstructure boundaries facing the cargo area

IGC Code chapter 11 requires a water spray system to cool and protect exposed cargo tank domes, cargo tanks on deck, manifolds, cargo deck houses and superstructure boundaries facing the cargo area against fire.

24. The introduction of fresh air into a tank to remove toxic, flammable and inert gases and raise the oxygen content to 21% by volume is called?

A. Ventilating
B. Purging
C. Aerating
D. Inerting

Answer: C — Aerating

In gas carrier terminology aeration is the final stage of gas freeing. Fresh dry air replaces inert gas and any remaining cargo vapour until the oxygen content reaches 21% by volume, so the tank is safe for entry.

25. When cargo is being discharged from a refrigerated ship into pressurised storage, it is necessary to ____ the cargo, usually to at least 0 degrees Celsius.

A. Cool or chill
B. Warm or heat
C. Freeze
D. Evaporate or vaporise

Answer: B — Warm or heat

Shore pressurised tanks are usually made of carbon steel that is not designed for low temperatures. Refrigerated cargo is therefore passed through the booster pump and cargo heater to raise it to about 0°C or above before it enters the shore tank.

26. The depth of liquid in a tank, measured from the bottom, is called the?

A. Draft
B. Ullage
C. Sounding
D. Freeboard

Answer: C — Sounding

A sounding is the depth of liquid measured from the tank bottom or datum up to the liquid surface. An ullage is the empty space measured from the top of the tank down to the liquid surface.

27. Which cargoes can cause a chemical burn in addition to a cold burn?

A. Butadiene
B. Propylene
C. Methane
D. Ethylene oxide, ammonia and chlorine

Answer: D — Ethylene oxide, ammonia and chlorine

Ethylene oxide, ammonia and chlorine are corrosive or reactive to body tissue. On skin contact they cause chemical burns as well as frostbite from the cold liquid, while hydrocarbons such as methane and propylene cause only cold burns.

28. When heat is added to or removed from a substance during a reversible process, the heat divided by the absolute temperature of the substance is called?

A. Internal energy
B. Enthalpy
C. Entropy
D. Gibbs free energy

Answer: C — Entropy

Entropy change is defined as dS = dQ/T for a reversible process, where dQ is the heat transferred and T is the absolute temperature. Entropy charts are used when analysing reliquefaction cycles.

29. Which cargo inhibitor is highly toxic, so that great care must be taken when handling it?

A. Sodium hydroxide
B. Diethyl ether
C. Phosphoric acid
D. Tertiary butyl catechol (TBC)

Answer: D — Tertiary butyl catechol (TBC)

Tertiary butyl catechol is the inhibitor commonly added to butadiene and other monomers to prevent polymerisation. It is toxic and corrosive to skin and eyes, so full protective equipment is needed when handling it or the inhibitor certificate samples.

30. Under what conditions can a gas be liquefied?

A. High temperature (heating) and low pressure (expansion)
B. Low temperature (cooling) and high pressure (compression)
C. Low temperature (cooling) and low pressure (expansion)
D. High temperature (heating) and high pressure (compression)

Answer: B — Low temperature (cooling) and high pressure (compression)

A gas is liquefied by cooling it below its boiling point and/or compressing it, provided it is below its critical temperature. Reliquefaction plants use both compression and cooling to condense boil-off vapour.

Set 18 — 30 GASCO exit exam questions with answers

1. Under the IGC Code (unharmonised survey scheme), the intermediate survey should be conducted at intervals not exceeding how many months?

A. 24 months
B. 36 months
C. 48 months
D. 30 months

Answer: D — 30 months

Under the original IGC survey requirements, an intermediate survey for the Certificate of Fitness was required at intervals not exceeding 30 months. Under the harmonised system it falls within three months of the second or third anniversary date.

2. When gassing up with which cargo would you not use inert gas from a combustion-type generator?

A. Propane
B. Methane
C. Ethylene
D. Ammonia

Answer: D — Ammonia

Combustion inert gas contains carbon dioxide, which reacts with ammonia to form solid carbamates that can block lines, valves and filters. Tanks for ammonia are therefore inerted with nitrogen, or gassed up directly from air.

3. Which is the worst condition that can lead to cavitation in a centrifugal pump?

A. Steady and uniform flow conditions
B. A high suction pressure
C. Vapour pockets formed in the suction flow stream
D. A low discharge pressure

Answer: C — Vapour pockets formed in the suction flow stream

Cavitation occurs when suction pressure falls below the liquid's vapour pressure. Vapour pockets form in the suction stream and collapse violently at the impeller, causing noise, vibration, loss of head and erosion. This is critical with boiling liquefied gas cargoes.

4. ____ means replacing an inert atmosphere in a tank with vapour from the next cargo to a suitable level to allow cooling down and loading.

A. Purging
B. Venting
C. Gassing up
D. Blanketing

Answer: C — Gassing up

Gassing up replaces the inert gas in a cargo tank with vapour of the cargo to be loaded. This removes non-condensable gases that would hinder reliquefaction and prepares the tank for cool-down.

5. What is the typical composition of inert gas produced by an inert gas generator?

A. Mainly nitrogen (about 85%) and carbon dioxide (about 14%), with oxygen below 0.5%
B. Mainly carbon dioxide (about 85%) with about 15% nitrogen
C. Pure nitrogen with about 5% oxygen
D. Mainly argon and hydrogen

Answer: A — Mainly nitrogen (about 85%) and carbon dioxide (about 14%), with oxygen below 0.5%

An oil-fired inert gas generator burning fuel with near-stoichiometric air produces roughly 85% nitrogen and 14% carbon dioxide, with small amounts of CO, SOx and water vapour. On gas carriers oxygen is kept below about 0.5%.

6. An uncontrolled liquid or vapour release can occur through?

A. Lightning strikes or electrical malfunctions only
B. Overfilling of tanks, unforeseen opening of relief valves, hose bursting or pipe fracture, and tank or pipe leakage
C. Excessive cleanliness of tanks
D. Thermal expansion of the accommodation

Answer: B — Overfilling of tanks, unforeseen opening of relief valves, hose bursting or pipe fracture, and tank or pipe leakage

The main causes of cargo release on gas carriers are tank overfilling, relief valves lifting unexpectedly, hose or pipe failure, and leaks from tanks or piping. ESD systems, high-level alarms and careful hose handling are designed to prevent these.

7. Some liquefied gas cargoes that are unstable or reactive may be stabilised before sailing by adding?

A. An inhibitor or additives
B. Water or moisture
C. Oxygen
D. Light or UV stabilisers

Answer: A — An inhibitor or additives

Monomers such as butadiene and vinyl chloride may polymerise or react, so an inhibitor is added before shipment. The IGC Code requires an inhibitor certificate giving the inhibitor's name, amount, date added and expected lifetime.

8. What is the critical pressure (bar absolute) of n-butane?

A. 25.0 to 25.5
B. 45.0 to 45.5
C. 30.0 to 30.5
D. 38.1 to 38.2

Answer: D — 38.1 to 38.2

n-Butane has a critical temperature of about 152°C and a critical pressure of about 38 bar absolute. Above 152°C it cannot be liquefied by pressure alone.

9. Where are spring-loaded relief valves commonly used on gas carriers?

A. In cargo pipelines, plant components and smaller cargo tanks
B. In the crew quarters
C. In the fresh water supply system
D. In the engine exhaust system

Answer: A — In cargo pipelines, plant components and smaller cargo tanks

Spring-loaded relief valves are used on cargo pipelines (for example to relieve liquid trapped between closed valves), on plant components such as heat exchangers and compressors, and on smaller pressure tanks. Large cargo tanks usually have pilot-operated valves.

10. The airlock should be fitted with?

A. No safety features
B. A fixed gas detection system
C. A high-pressure release valve
D. An open flame source

Answer: B — A fixed gas detection system

Airlocks between gas-dangerous and gas-safe spaces must be mechanically ventilated and monitored for cargo vapour, with gas detection and alarms. This ensures dangerous gas cannot pass into accommodation or machinery spaces.

11. How are the pump suction capacity and the resulting discharge rate regulated?

A. By increasing the pump rate, opening the discharge valve fully and using a bypass
B. By disconnecting the pump, closing the discharge valve and increasing discharge pressure
C. By stopping the pump, opening the suction valve fully and reducing discharge pressure
D. By reducing the pump speed, throttling the discharge valve or using a bypass (return valve)

Answer: D — By reducing the pump speed, throttling the discharge valve or using a bypass (return valve)

The discharge rate of a cargo pump is controlled by changing pump speed where possible, throttling the discharge valve, or recirculating part of the flow back to the tank through a bypass or return valve. The suction is never throttled, as this causes cavitation.

12. Vapour removed from contact with its liquid and heated beyond its boiling temperature is called?

A. Subcooled vapour
B. Condensed liquid
C. Superheated vapour
D. Saturated vapour

Answer: C — Superheated vapour

Saturated vapour is in equilibrium with its liquid at the boiling temperature. Once vapour is separated from its liquid and heated above that temperature, it becomes superheated vapour.

13. Air-driven lamps of an approved type may be used in dangerous or hazardous areas. To avoid accumulation of static electricity at the appliance, which precautions should be observed?

A. The air supply should be connected to a high-voltage power source
B. The supply hose should be made of insulating material
C. The air supply should have a water trap, the supply hose should be of low electrical resistance, and permanently installed units should be earthed
D. No precautions are needed, as air-driven lamps are inherently safe

Answer: C — The air supply should have a water trap, the supply hose should be of low electrical resistance, and permanently installed units should be earthed

ISGOTT advises that air-driven lamps have a water trap in the air supply and a low-resistance supply hose, and that permanent installations be earthed. This stops static charge building up on the lamp, which could cause an incendive spark.

14. Absolute zero temperature is equal to how many degrees Celsius?

A. 0 degrees Celsius
B. 273.15 degrees Celsius
C. -273.15 degrees Celsius
D. 100 degrees Celsius

Answer: C — -273.15 degrees Celsius

Absolute zero is 0 kelvin, the lowest possible temperature, at which molecular motion is at a minimum. Since 0°C equals 273.15 K, absolute zero is -273.15°C.

15. What does the initial survey include before a ship is put into service or before the Certificate of Fitness is issued for the first time?

A. Inspection of crew qualifications
B. Assessment of environmental conditions around the ship
C. Verification of the ship's insurance cover
D. A complete survey of the structure, equipment, fittings, arrangements and material of the ship

Answer: D — A complete survey of the structure, equipment, fittings, arrangements and material of the ship

Under the IGC Code the initial survey, carried out before the ship enters service or before the International Certificate of Fitness is first issued, is a complete survey of the ship's structure, equipment, fittings, arrangements and materials covered by the Code.

16. Access from a gas-dangerous zone on the open weather deck to a gas-safe space must be via an air lock consisting of ____ substantially gastight steel doors spaced at least 1.5 m but not more than 2.5 m apart.

A. 2
B. 0
C. 4
D. 1

Answer: A — 2

The IGC Code requires an air lock to have two self-closing, substantially gastight steel doors spaced at least 1.5 m and not more than 2.5 m apart, so that both cannot easily be open at once.

17. What is the critical temperature of n-butane?

A. -82.6 degrees Celsius
B. 153 degrees Celsius
C. 96.7 degrees Celsius
D. 9.2 degrees Celsius

Answer: B — 153 degrees Celsius

n-Butane has a critical temperature of about 152 to 153°C, well above ambient, so it can easily be liquefied by pressure alone. Methane, propane and ethylene all have lower critical temperatures than butane.

18. Why are cargo vaporisers required on gas carriers?

A. To produce vapour that may be needed for gassing up tanks
B. To increase the liquid cargo temperature before discharge
C. To cool down the cargo tanks during loading
D. To release excess pressure from the cargo tanks

Answer: A — To produce vapour that may be needed for gassing up tanks

A vaporiser turns liquid cargo into vapour. It is used to gas up tanks, especially when no shore vapour is available, and to supply vapour that keeps tank pressure up during discharge without vapour return. Warming liquid is the job of the cargo heater.

19. What are the main categories of cargo containment systems?

A. Unattached tanks, temporary tanks, external tanks
B. Permeable tanks, composite tanks, externally insulated tanks
C. Integral tanks, independent tanks, membrane tanks, semi-membrane tanks, internal insulation tanks
D. Conductive tanks, radiant tanks, exothermic tanks

Answer: C — Integral tanks, independent tanks, membrane tanks, semi-membrane tanks, internal insulation tanks

IGC Code chapter 4 classifies cargo containment systems as integral, membrane, semi-membrane, independent Type A, B and C and internal insulation tanks. Each type has its own design and secondary barrier requirements.

20. As per the IGC Code, cargo tank temperature indication requires at least ____ devices.

A. 0
B. 2
C. 1
D. 5

Answer: B — 2

The IGC Code requires each cargo tank to have at least two devices for indicating cargo temperature, one at the bottom of the tank and one near the top below the highest allowable liquid level, so that temperature can be monitored during cool-down and voyage.

21. Which is a typical hydrate inhibitor?

A. Nitrogen
B. Carbon dioxide
C. Water
D. Methanol

Answer: D — Methanol

Methanol (like glycols) acts as an antifreeze. It lowers the temperature at which hydrates form and is injected into pump suctions and lines on LPG carriers to stop hydrates blocking pumps, valves and filters.

22. Compared to globe and angle valves, gate valves will:

A. Give a higher pressure drop when fully open
B. Operate with little or no pressure drop when fully open
C. Have a similar pressure drop to globe and angle valves
D. Always function better in high-temperature conditions

Answer: B — Operate with little or no pressure drop when fully open

A fully open gate valve leaves a straight, unobstructed flow path, so its pressure drop is very small. Globe and angle valves force the flow to change direction through the seat, which creates much higher resistance.

23. In all gas trades it is essential that the ship and terminal operators are:

A. Unaware of each other's emergency procedures
B. Lacking knowledge of the cargo handling equipment
C. Unfamiliar with emergency shutdown procedures
D. Familiar with the basic characteristics of each other's facilities, aware of the division of responsibilities and able to communicate effectively

Answer: D — Familiar with the basic characteristics of each other's facilities, aware of the division of responsibilities and able to communicate effectively

SIGTTO and ISGOTT guidance stress that safe cargo transfer depends on ship and terminal understanding each other's equipment, agreeing who is responsible for what in the ship/shore safety checklist, and keeping effective communication throughout the port call.

24. How many non-return valves, or equivalent, are fitted in the inert gas main to prevent backflow of cargo vapour?

A. 5
B. 20
C. 2
D. None

Answer: C — 2

The IGC Code requires two non-return valves or equivalent devices in the inert gas main where it connects to the cargo system. This prevents cargo vapour or liquid flowing back into the inert gas plant in gas-safe spaces.

25. The main hazards of a liquefied gas vapour cloud are?

A. Transparency
B. Invisibility
C. Flammability, toxicity and low temperature
D. Buoyancy

Answer: C — Flammability, toxicity and low temperature

A vapour cloud from spilled liquefied gas may be flammable, toxic or asphyxiating, and very cold, causing frostbite and brittle fracture of steel. These hazards decide the emergency response and the area that must be kept clear.

26. Hydrates are snow-like compounds of?

A. Carbon dioxide and methane
B. Hydrocarbon and water
C. Oxygen and nitrogen
D. Sulphur and hydrogen

Answer: B — Hydrocarbon and water

Hydrates are ice-like crystalline compounds that form when free water combines with hydrocarbons such as propane or butane under certain conditions of pressure and temperature. They can block pumps, valves and instrument lines.

27. What is the critical pressure (bar absolute) of propane?

A. 58.4
B. 36.2
C. 42.6
D. 25.8

Answer: C — 42.6

Propane has a critical temperature of about 96.7°C and a critical pressure of about 42.5 bar absolute. Fully pressurised LPG tanks are designed for a vapour pressure of around 18 bar, well below this.

28. One source of pollution from gas cargoes is the release of ____ vapours from the LPG condenser of the reliquefaction plant.

A. Sulphur-containing
B. Water-soluble
C. Odourless
D. Incondensable

Answer: D — Incondensable

Non-condensable gases such as nitrogen, inert gas and some cargo vapour collect in the condenser and must be vented. This release carries cargo vapour to atmosphere, so careful gassing up and purging are needed to keep incondensables to a minimum.

29. Which factors influence a pump's suction condition?

A. The colour of the liquid
B. The ambient temperature only
C. The pump's NPSH, the cargo tank pressure, the liquid level and the cargo vapour pressure
D. The ship's draft

Answer: C — The pump's NPSH, the cargo tank pressure, the liquid level and the cargo vapour pressure

The available suction head depends on tank pressure, liquid level above the pump and the cargo's vapour pressure. This must exceed the pump's required NPSH or the cargo boils at the impeller and cavitates, which is critical with boiling liquefied gases.

30. The ratio of the density of a liquid at a given temperature to the density of fresh water at a standard temperature is called?

A. Dynamic viscosity
B. Specific gravity
C. Vapour pressure
D. Surface tension

Answer: B — Specific gravity

Specific gravity, or relative density, is the density of a liquid divided by the density of fresh water at a standard temperature. It has no units, and cargo calculations use it to convert volume into mass.

Set 19 — 30 GASCO exit exam questions with answers

1. Earthing and bonding minimise the dangers arising from?

A. Low temperatures
B. The accumulation of electrostatic charge
C. High humidity
D. Stable atmospheric conditions

Answer: B — The accumulation of electrostatic charge

Earthing and bonding connect conductive items so that electrostatic charge drains away safely instead of building up a potential difference that could discharge as an incendive spark in a flammable atmosphere, as described in ISGOTT.

2. At constant pressure, when the temperature of a gas increases, its volume:

A. Increases
B. Remains constant
C. Decreases
D. Becomes negative

Answer: A — Increases

By Charles's law the volume of a fixed mass of gas at constant pressure is directly proportional to its absolute temperature. Raising the temperature therefore increases the volume.

3. Before starting a cargo compressor, the condenser cooling system must be operating, with either R22 circulating or the system running on ____.

A. Nitrogen
B. Vacuum
C. Steam
D. Seawater

Answer: D — Seawater

In a reliquefaction plant, compressed cargo vapour is condensed either in a seawater-cooled condenser or in a cascade system cooled by R22 or another refrigerant. Cooling must be running first, or condenser pressure and temperature rise rapidly and the compressor trips.

4. What is the liquid relative density of propane at its atmospheric boiling point (water = 1)?

A. 1.0
B. 0.584
C. 0.946
D. 1.267

Answer: B — 0.584

At its atmospheric boiling point of about -42°C, liquid propane has a relative density of about 0.58, so it is much lighter than water and floats on it if spilled.

5. What is the unique property of carbon atoms, allowing them to link with each other to form chains and rings, called?

A. Isomerism
B. Dissociation
C. Catenation
D. Hydration

Answer: C — Catenation

Catenation is the ability of carbon atoms to bond to one another, forming long chains, branches and rings. This is why there are so many hydrocarbons and other organic compounds.

6. Hydrocarbons with up to four carbon atoms in their molecules are ____ at ambient temperature.

A. Solids
B. Gases
C. Liquids
D. Plasmas

Answer: B — Gases

Methane, ethane, propane and butane (C1 to C4) are gases at normal ambient temperature and pressure. They must be refrigerated or pressurised to be carried as liquids, while C5 and heavier hydrocarbons are liquids.

7. The discharge rate should not be reduced by throttling the ship's manifold valves when the shore cannot accept the rate, because throttling in this way would ____ the cargo.

A. Speed up
B. Heat
C. Stabilise
D. Cool down

Answer: B — Heat

Throttling the discharge against a running cargo pump turns pump energy into heat in the liquid. This raises cargo temperature and vapour pressure and can cause flashing. The rate should instead be reduced by pump speed control or by recirculating.

8. A certificate issued by a classification society surveyor to allow a vessel that has met with a mishap affecting its seaworthiness to proceed, after temporary repairs, to another port where permanent repairs can be carried out, is called a?

A. Mishap clearance certificate
B. Temporary repairs certificate
C. Emergency navigation certificate
D. Seaworthiness certificate

Answer: D — Seaworthiness certificate

After an accident, the class surveyor inspects the temporary repairs and may issue a certificate of seaworthiness, often with a condition of class, allowing the ship to sail to a repair port where permanent repairs will be completed.

9. Which is the correct sequence of operations, from the previous cargo to loading the next cargo?

A. Purging of cargo tanks, gassing up, aeration, warming up, cooling down, liquid freeing, mopping and drying, re-inerting, drying
B. Cooling down, gassing up, aeration, warming up, purging of cargo tanks, liquid freeing, drying, re-inerting, mopping and drying
C. Liquid freeing, warming up, purging of cargo tanks, aeration, mopping and drying, re-inerting, drying, gassing up, cooling down
D. Warming up, gassing up, purging of cargo tanks, aeration, liquid freeing, re-inerting, drying, mopping and drying, cooling down

Answer: C — Liquid freeing, warming up, purging of cargo tanks, aeration, mopping and drying, re-inerting, drying, gassing up, cooling down

After discharge, the remaining liquid is removed and the tanks warmed. Vapour is then purged with inert gas and the tank aerated for inspection and cleaning. It is dried and re-inerted, then gassed up with the new cargo vapour and finally cooled down for loading.

10. What is the difference between an independent Type A tank and an independent Type C tank?

A. An independent Type C tank needs a full secondary barrier
B. Both types need only a partial secondary barrier
C. Neither type needs any secondary barrier
D. An independent Type A tank needs a full secondary barrier

Answer: D — An independent Type A tank needs a full secondary barrier

Type A tanks are designed by conventional structural analysis, so the IGC Code requires a complete secondary barrier for cargoes below -10°C. Type C tanks are pressure vessels with a high safety margin against failure and need no secondary barrier.

11. With reference to LNG operations, what does the term 'rollover' describe?

A. Two or more stratified layers of LNG of different density in the same tank suddenly mixing, causing a rapid increase in boil-off
B. A controlled, planned process of mixing grades of LNG in the same tank to achieve a desired composition
C. The process of separating layers of LNG in a tank to prevent rapid vaporisation
D. A condition where LNG in the tank stays completely stratified without any mixing

Answer: A — Two or more stratified layers of LNG of different density in the same tank suddenly mixing, causing a rapid increase in boil-off

Rollover happens when layers of LNG of different density and temperature form in a tank. The lower layer warms and becomes less dense until the layers suddenly overturn and mix, releasing a large volume of boil-off that can overpressurise the tank.

12. Apart from other checks, which types of atmospheric analysis need to be carried out on gas carriers?

A. Colour spectrum, radioactivity and humidity
B. Metallic content, particle size distribution and aromatic hydrocarbons
C. Air pressure, wind speed and solar radiation
D. Flammability, toxicity and oxygen content

Answer: D — Flammability, toxicity and oxygen content

On gas carriers tank and space atmospheres are tested for flammable vapour against the LFL, for toxic gases against exposure limits, and for oxygen content, both for safe entry and to verify inerting and gas-freeing operations.

13. What is a purpose of the reliquefaction plant on a gas carrier?

A. To heat up the cargo tanks and raise the temperature before loading
B. To pressurise the cargo tanks during unloading
C. To cool down the cargo tanks and associated pipelines before loading
D. To introduce oxygen into the cargo tanks for safety

Answer: C — To cool down the cargo tanks and associated pipelines before loading

Besides reliquefying boil-off on passage to control tank pressure, the reliquefaction plant is used to cool tanks and lines before loading. It condenses the vapour produced when cargo is sprayed into the warm tanks and returns it as liquid.

14. A process that is accompanied by the absorption of heat is called?

A. Exothermic
B. Endothermic
C. Isobaric
D. Isothermal

Answer: B — Endothermic

An endothermic process takes in heat from its surroundings, such as liquefied gas vaporising in a vaporiser. An exothermic process gives out heat, such as combustion or polymerisation.

15. When discharging cargo into pressurised storage, the cargo booster pump and cargo heater run in ____ with the cargo pump.

A. Opposite direction
B. Intermittent cycles
C. Parallel
D. Series

Answer: D — Series

When discharging refrigerated cargo to pressurised shore tanks, the deepwell or submerged cargo pump delivers to the booster pump, which then passes the cargo through the heater. They operate in series to give the extra pressure and the warming needed for the shore tanks.

16. You are discharging a cargo of propane and the cargo tank pressure is falling quickly. What would you do to maintain a steady pressure?

A. Increase the discharging rate to make up for the falling pressure
B. Slow down the discharging rate
C. Ignore the falling pressure and continue at the same rate
D. Stop discharging to prevent further pressure loss

Answer: B — Slow down the discharging rate

If tank pressure falls rapidly during discharge without vapour return, the liquid is being removed faster than vapour can form. Reducing the discharge rate, and if needed using the vaporiser or shore vapour return, prevents low pressure and pump cavitation.

17. Irrespective of ship type, cargo tanks should be located not less than ____ from the moulded line of the bottom shell plating at the centreline.

A. B/25 or 1.5 m, whichever is greater
B. B/10 or 3 m, whichever is greater
C. B/20 or 1 m, whichever is greater
D. B/15 or 2 m, whichever is less

Answer: D — B/15 or 2 m, whichever is less

IGC Code chapter 2 requires that, for all ship types, cargo tanks be located at least B/15 or 2 m, whichever is less, above the moulded line of the bottom shell plating at the centreline, to protect them in case of grounding damage.

18. What must be considered when changing cargo grade?

A. Ignore compatibility, vapour concentration and oxygen content
B. Consider only the maximum vapour concentration from the last cargo
C. Compatibility of the previous and next cargoes, the maximum vapour concentration of the last cargo and the maximum oxygen content allowed
D. Consider oxygen content only

Answer: C — Compatibility of the previous and next cargoes, the maximum vapour concentration of the last cargo and the maximum oxygen content allowed

When changing grade on a gas carrier, the new cargo must be compatible with the previous one, and the remaining vapour must be reduced to the level required by the charterer or terminal. The oxygen content must also be below the limit for the next cargo, as for butadiene or VCM.

19. In a polarographic oxygen cell, when a potential is applied, oxygen is reduced at the ____ in the presence of KCl electrolyte.

A. Anode
B. Cathode
C. Electrolyte
D. Both electrodes

Answer: B — Cathode

In a polarographic (Clark-type) oxygen sensor, oxygen diffusing through the membrane is reduced at the cathode while the anode is oxidised in the KCl electrolyte. The resulting current is proportional to the oxygen partial pressure.

20. In the conductometric method, the difference in gas conductivity before and after passing the sample gas denotes which of the following?

A. Efficiency of the cell
B. Quantity of reagent
C. Concentration of gas
D. Density of the reagent

Answer: C — Concentration of gas

In conductometric analysis the sample gas is absorbed in a reagent solution, changing its electrical conductivity. The change in conductivity measured before and after the sample passes is proportional to the concentration of the gas being analysed.

21. Which of the following is the widely used method for trace gas analysis?

A. Galvanic method
B. Conductometric method
C. Polarographic cells
D. Thermal conductivity method

Answer: B — Conductometric method

The conductometric method is highly sensitive because even very small amounts of absorbed gas produce a measurable change in reagent conductivity, making it the widely used technique for trace gas analysis in instrumentation practice.

22. The polarographic cell type of electrochemical method uses which of the following concepts?

A. Cyclic reactions
B. Exothermic reactions
C. Reversible reactions
D. Redox reactions

Answer: D — Redox reactions

A polarographic cell applies a polarising voltage across electrodes; oxygen diffusing through the membrane is reduced at the cathode while oxidation occurs at the anode. This redox (reduction-oxidation) reaction produces a current proportional to the oxygen partial pressure.

23. Which of the following is true about the Hersch cell, which is one of the arrangements of the galvanic cell?

A. The cell is spherical in shape
B. The cathode is made of porous material
C. The cathode is placed centrally
D. The cathode is formed by a gauze which surrounds the anode

Answer: D — The cathode is formed by a gauze which surrounds the anode

In the Hersch galvanic oxygen cell the cathode is a metal gauze (typically silver) wrapped around the base-metal anode, giving a large contact area for the sample gas and electrolyte so that oxygen reduction generates a measurable current.

24. Which of the following is NOT true about the galvanic method of oxygen analysis?

A. Electrodes are composed of noble and base metals
B. It can measure the dissolved content of oxygen
C. Its principle is based on electrolysis
D. It utilises an electrochemical cell

Answer: C — Its principle is based on electrolysis

A galvanic cell generates its own current from the chemical reaction between oxygen and the noble/base metal electrodes; no external voltage is applied. Electrolysis requires an external supply driving the reaction, so stating that the galvanic method is based on electrolysis is incorrect.

25. After completing the rigging, what action should be carried out to ensure that the auxiliary (emergency) cargo pump is cooled down slowly and sufficiently?

A. Leave the pump suspended in the empty column for 10 to 12 hours
B. Stop all operations immediately
C. Increase the cargo tank pressure gradually
D. Immediately drop the pump to the bottom of the column for direct contact with LNG

Answer: A — Leave the pump suspended in the empty column for 10 to 12 hours

The emergency cargo pump is left suspended in the column so that cold vapour gradually cools it over several hours. Sudden contact with LNG would cause thermal shock, uneven contraction and possible damage to bearings and the pump casing.

26. What can deterioration or failure of cargo tank insulation efficiency result in?

A. Lower inner hull steel temperature and higher boil-off from the cargo tank
B. Higher inner hull steel temperature and lower boil-off from the cargo tank
C. Higher inner hull steel temperature and higher boil-off from the cargo tank
D. Lower inner hull steel temperature and lower boil-off from the cargo tank

Answer: A — Lower inner hull steel temperature and higher boil-off from the cargo tank

When insulation deteriorates, more heat flows from the hull into the cargo. The inner hull steel becomes colder (risking brittle fracture, cold spots) and the extra heat ingress increases the boil-off rate from the affected tank.

27. Which alarm is expected to be activated when minor damage to the membrane has occurred?

A. Water detection in insulation space
B. Gas detection in insulation space
C. Tank level high
D. Tank pressure high

Answer: B — Gas detection in insulation space

A leak in the primary membrane allows cargo vapour into the nitrogen-filled insulation space. The continuous gas detection system sampling the insulation spaces will therefore register methane and raise an alarm, giving early warning of membrane damage.

28. Which typical detection system is provided on board to give an early indication that the inner hull is experiencing structural failure?

A. Alarm: low oxygen reading in primary insulation space
B. Alarm: water detected in secondary insulation space
C. Alarm: ballast water temperature low
D. Alarm: water detected in primary insulation space

Answer: B — Alarm: water detected in secondary insulation space

On membrane LNG carriers the secondary insulation space lies directly against the inner hull. A crack in the inner hull lets ballast water leak into this space, so water detectors fitted in the secondary insulation space give the earliest indication of inner hull failure.

29. Identify the odd one. On board an LNG tanker with a No. 96 containment system, which of the following is NOT an indication of membrane failure?

A. Sudden rise in cargo tank pressure in the affected cargo tank
B. Sudden drop of inner hull temperatures
C. Sudden rise of methane concentration in the primary space of the affected cargo tank
D. Sudden rise of pressure in the primary insulation space of the affected cargo tank

Answer: A — Sudden rise in cargo tank pressure in the affected cargo tank

A membrane leak transfers cargo into the insulation space, raising methane concentration and pressure there and chilling the inner hull. Cargo tank pressure itself is not noticeably affected, since the tank loses a little vapour rather than gaining it.

30. What are the typical methods to check cargo tank insulation?

A. Frequent inspection of the inner hull and monitoring of the temperature sensors
B. Frequent measuring of ballast water temperature readings
C. Frequent measuring of ballast water density readings
D. Frequent observation for ice in ballast water

Answer: A — Frequent inspection of the inner hull and monitoring of the temperature sensors

Insulation efficiency is monitored by inner hull temperature sensors and by regular inspections of the ballast and cofferdam spaces for cold spots. A local drop in hull temperature indicates insulation deterioration long before other effects become visible.

Set 20 — 30 GASCO exit exam questions with answers

1. When a minor spill cannot be stopped, what is the next action to be taken?

A. Continuously monitor the spillage without taking any action
B. Increase the rate of operation so that the spill might seal by itself
C. Inject the cargo line with CO2 without stopping the cargo operation
D. Suspend the cargo operation until the fault has been rectified

Answer: D — Suspend the cargo operation until the fault has been rectified

If a leak cannot be stopped immediately, cargo transfer must be stopped (ESD if necessary) and not resumed until the defect is repaired. ISGOTT and SIGTTO guidance require operations to be suspended whenever a cargo leak threatens safety.

2. Which of the following precautions need NOT be strictly adhered to while rigging and working near the open cargo pump column?

A. Avoid anything falling inside the cargo pump column
B. Keep the column opening covered at all times with a temporary special cover
C. All personnel involved must empty their pockets before working
D. All personnel must be well dressed in uniforms

Answer: D — All personnel must be well dressed in uniforms

The critical precautions prevent foreign objects dropping into the open pump column, which could damage the pump or the tank. Covering the opening and emptying pockets serve this purpose; wearing uniforms has no bearing on that risk, beyond normal PPE.

3. What can happen if the auxiliary cargo pump column is filled too fast with LNG?

A. The column may collapse due to vacuum formation
B. The pump may be dislodged and damaged by the rush of liquid into the pump well
C. The cargo tank level transmitter reading may be interrupted
D. The cargo pump impeller may heat up, causing overpressure in the column

Answer: B — The pump may be dislodged and damaged by the rush of liquid into the pump well

When the foot valve is opened, LNG rushes into the emergency pump well. If filling is too rapid, the surge and sudden thermal contraction can lift or dislodge the pump from its seat and damage it, so the column is flooded slowly.

4. Which of the following typical locations on board an LNG tanker has the lowest risk of cargo (LNG) spillage?

A. A primary insulation space valve
B. A liquid manifold
C. Vaporiser inlet valve
D. Underneath a cargo valve

Answer: A — A primary insulation space valve

Insulation space valves handle only nitrogen and never carry liquid cargo. The manifold, vaporiser inlet and cargo valves all handle LNG under pressure and are the classic leak points, which is why drip trays and water curtains are provided there.

5. On board a membrane-type LNG carrier, during drying operations it is important to ensure the cargo tank pressure is above the primary insulation space pressure. This is to avoid ____.

A. Long drying time
B. Inward collapse of the primary barrier
C. Freezing of nitrogen inside the insulation space
D. Rust formation on the primary barrier surface

Answer: B — Inward collapse of the primary barrier

The thin stainless or Invar primary membrane cannot withstand reverse pressure. If the insulation space pressure exceeds the tank pressure, the membrane can be pushed inward and collapse, so tank pressure is always kept higher than the interbarrier space.

6. During loading and discharging operations, why is cargo sampling carried out ashore by the cargo surveyor?

A. To satisfy MARPOL regulations
B. To verify cargo composition, heating value and density
C. To satisfy IGC Code regulations
D. To check flow in the line by venting the line

Answer: B — To verify cargo composition, heating value and density

LNG is sold on energy content, so custody transfer requires the cargo's composition, density and gross heating value. Samples taken during transfer are analysed by gas chromatograph to calculate the energy delivered, which forms the basis of the commercial invoice.

7. On an LNG tanker, why is cooling down of the cargo lines necessary before discharging?

A. To increase the flow rate of LNG while discharging
B. To reduce air-locks within the pipeline before discharging
C. To ensure all pipelines are cold to avoid thermal shock
D. To maximise cargo boil-off prior to discharging

Answer: C — To ensure all pipelines are cold to avoid thermal shock

Introducing LNG at -160°C into warm pipework causes rapid uneven contraction, high stresses and violent flashing. Lines and arms are therefore cooled gradually beforehand to prevent thermal shock, pressure surges and possible damage to piping, joints and valves.

8. Identify the equipment used for generating warm LNG vapour.

A. Demister
B. Cargo gas heaters
C. Forced vaporiser
D. Barrier punch device

Answer: B — Cargo gas heaters

Warm vapour for warming-up operations and fuel gas supply is produced by passing compressed boil-off gas through the steam-heated cargo gas heaters. The forced vaporiser converts liquid into cold vapour, while a demister only removes droplets.

9. What is the purpose of cooling down cargo tanks prior to loading?

A. To lower the temperature of the cargo tanks to receive LNG
B. To increase the pressure in the cargo tank to receive LNG
C. To reduce air turbulence in the cargo tank to receive LNG
D. To cool down the nitrogen in the insulation spaces

Answer: A — To lower the temperature of the cargo tanks to receive LNG

Cargo tanks must be cooled gradually to near cargo temperature before bulk loading. This limits thermal stresses in the containment system and prevents excessive vapour generation and tank overpressure when LNG first enters a warm tank.

10. On board an LNG tanker during a loaded sea voyage, how is controlled venting of boil-off carried out?

A. Vented via the common main mast riser
B. Vented via the funnel
C. Vented via a shipside vent tube
D. Vented via the vapour manifold

Answer: A — Vented via the common main mast riser

When boil-off cannot be burnt or reliquefied, it is released in a controlled manner through the vapour header to the forward (main mast) vent riser. This discharges gas high above the deck away from accommodation and ignition sources, as required by the IGC Code.

11. During the interface (compatibility) study for ship approval by a terminal operator, what takes place?

A. Preliminary discussions on operating rates and finance
B. Preliminary discussions, document analysis and mooring pattern
C. Document analysis, cargo details and finance
D. Preliminary discussions on crew competence and cargo analysis

Answer: B — Preliminary discussions, document analysis and mooring pattern

A ship/shore compatibility study begins with preliminary discussions, followed by analysis of the ship's documents and particulars, manifold arrangement and a mooring analysis for the berth, to confirm the vessel can safely berth and transfer cargo at that terminal.

12. On board an LNG tanker, which equipment is used to generate vapour during the forced boil-off operation?

A. Forced vaporiser
B. Forced nitrogen generator
C. Forced inert gas generator
D. Forced gas compressor

Answer: A — Forced vaporiser

When natural boil-off is insufficient for fuel demand, LNG is pumped by the stripping/spray pump to the forced vaporiser, where it is evaporated by steam heating. The vapour is then supplied to the boilers or engines as fuel gas.

13. On an LNG tanker during discharging, why is it necessary to stop one of the two main cargo pumps when finishing cargo at about 0.8 m?

A. To avoid overflowing of shore tanks
B. To reduce the excessive turbulence created at the suction of both main cargo pumps
C. To control cargo tank pressure when finishing cargo
D. To maintain insulation space pressure

Answer: B — To reduce the excessive turbulence created at the suction of both main cargo pumps

At low liquid levels, two pumps running together draw down the liquid rapidly and create vortices and turbulence at the suctions, leading to loss of suction and cavitation. Running one pump allows smooth stripping to the minimum level.

14. Why do we need to rig the auxiliary (emergency) cargo pump?

A. Because all other pumps inside the tank are out of order
B. To test it on board
C. Because the terminal requests it
D. To increase the maximum rate of discharge

Answer: A — Because all other pumps inside the tank are out of order

The emergency cargo pump is lowered into the emergency pump column only when the main cargo pumps in that tank have failed, so that cargo can still be discharged. It is a back-up arrangement and not used to increase rates.

15. Identify the odd one. On board an LNG tanker, which of these equipment is NOT required for gas burning?

A. Gas heater
B. Vacuum pump
C. Steam dump on main condenser
D. LD compressor

Answer: B — Vacuum pump

For gas burning, the LD compressor delivers boil-off gas through the gas heater to the boilers, and the steam dump to the main condenser handles excess steam when gas must be burnt at low load. A vacuum pump plays no part in this system.

16. Pressurising the insulation spaces with nitrogen and maintaining a pressure slightly above atmospheric prevents what?

A. Formation of explosive mixtures and ingress of moisture and air
B. Fall in cargo tank temperatures
C. Collapse of the inflated insulation boxes
D. Accidental formation of vacuum leading to membrane collapse

Answer: A — Formation of explosive mixtures and ingress of moisture and air

Nitrogen keeps the insulation spaces inert so that any leaking cargo cannot form a flammable mixture, and the slight positive pressure stops humid air entering. Moisture would degrade insulation and could freeze, so a dry inert atmosphere is maintained.

17. A soda-acid type water extinguisher is used to fight Class ____ fires.

A. A
B. B
C. C
D. D

Answer: A — A

Soda-acid extinguishers expel a jet of water and are suitable only for Class A fires involving ordinary combustible solids such as wood, paper and cloth. Water is unsuitable for flammable liquid, gas, metal or electrical fires.

18. Based on the principles of segregation, how would you classify the electric motor room on a gas carrier?

A. Gas-dangerous space
B. Gas-dangerous zone
C. Gas-safe zone
D. Gas-safe space

Answer: D — Gas-safe space

The cargo compressor electric motor room is separated from the compressor room by a gastight bulkhead with shaft seals and is kept under positive-pressure ventilation. Under the IGC Code it is therefore a gas-safe space, allowing ordinary electrical equipment.

19. What marking must be clearly visible on a crane?

A. Manufacturer's logo
B. Safe working load
C. Make of the crane
D. Date of last painting

Answer: B — Safe working load

Every crane and item of lifting gear must be clearly marked with its safe working load so that operators do not overload it. ILO Convention 152 and national lifting gear rules make the SWL marking mandatory, unlike manufacturer details.

20. BLEVE stands for "boiling liquid expanding vapour ____".

A. expansion
B. explosion
C. expression
D. evaporation

Answer: B — explosion

BLEVE means Boiling Liquid Expanding Vapour Explosion. It occurs when a vessel containing liquefied gas is heated by fire, the shell weakens and ruptures, and the superheated liquid flashes violently, often igniting as a fireball.

21. If the concentration of methane vapour in air is less than 5%, LNG vapours cannot burn because of inadequate ____.

A. LNG fuel
B. oxygen
C. nitrogen
D. heat

Answer: A — LNG fuel

The lower flammable limit of methane is about 5% by volume in air. Below this the mixture is too lean: there is plenty of oxygen but insufficient fuel to sustain combustion, so the vapour cannot ignite.

22. An air separation process is the most common system employed for producing ____ on ships.

A. oxygen
B. nitrogen
C. hydrogen
D. carbon dioxide

Answer: B — nitrogen

Gas carriers use nitrogen generators that separate compressed air, usually through hollow-fibre membranes or pressure-swing adsorption, delivering high-purity nitrogen for inerting insulation spaces, purging and seal gas.

23. Inert gas is used to eliminate ____ from the LNG tank while gas freeing.

A. hydrogen
B. LNG vapour
C. oxygen
D. carbon dioxide

Answer: B — LNG vapour

Before aeration, the tank is inerted to displace methane vapour. Going directly from cargo vapour to air would pass through the flammable range, so inert gas first purges the hydrocarbon content below a safe level.

24. The effect of layering made up of two vapours or gases of different densities is called ____.

A. Weathering
B. Stratification
C. Inerting
D. Diffusion

Answer: B — Stratification

Stratification is the formation of distinct layers when gases or liquids of different densities do not mix, the lighter remaining above the heavier. It is important during purging, gassing-up and inerting, where displacement efficiency depends on density differences.

25. ____ is the standard measurement of atmospheric pressure, corresponding to 760 mm (29.92 inches) of mercury.

A. 912.5 millibars
B. 1013.25 millibars
C. 1212.5 millibars
D. 1113.25 millibars

Answer: B — 1013.25 millibars

Standard atmospheric pressure is 101.325 kPa, i.e. 1013.25 mbar, equal to 760 mm or 29.92 inches of mercury. Gauges on cargo systems read relative to this value, so absolute pressure equals gauge pressure plus atmospheric.

26. ____ pressure is commonly used for measuring vacuum and pressures.

A. Absolute
B. Gauge
C. Atmospheric
D. Partial

Answer: B — Gauge

Most shipboard pressure and compound gauges read gauge pressure, i.e. pressure relative to the local atmosphere. Positive values indicate pressure above atmospheric and negative values indicate vacuum, which is convenient for operational monitoring of tanks and lines.

27. The temperature of 1 g of water can be increased by 1°C using ____.

A. 1 calorie
B. 10 calories
C. 5 calories
D. 100 calories

Answer: A — 1 calorie

The calorie is defined as the heat required to raise the temperature of one gram of water by one degree Celsius, about 4.19 joules. This reflects the specific heat capacity of water, 1 cal/g°C.

28. How is the inner hull void space (cofferdam) between the cargo tanks maintained at a temperature above 0°C during the loaded voyage?

A. By filling the void space between the tanks with heated glycol
B. By filling the void space between the tanks with hot water
C. By glycol-water heating coils, heated by steam or electric heaters, in each void space between the tanks
D. By circulating cold ballast water through the void spaces

Answer: C — By glycol-water heating coils, heated by steam or electric heaters, in each void space between the tanks

Membrane LNG carriers have a cofferdam heating system circulating heated glycol-water through coils in each transverse cofferdam. Heating keeps the steel above its minimum design temperature, preventing brittle fracture as required by the IGC Code.

29. Which two important gas laws concern the change of state of LNG from the gas field to the customer's kitchen?

A. Avogadro's hypothesis and Newton's third law
B. Charles's law and Avogadro's hypothesis
C. Boyle's law and Charles's law
D. Dalton's law and Hooke's law

Answer: C — Boyle's law and Charles's law

Natural gas is liquefied and regasified through changes of pressure, volume and temperature. Boyle's law relates pressure and volume at constant temperature, and Charles's law relates volume and temperature at constant pressure, together describing these changes.

30. ____ is the process of change in the composition of the mixture in the tank because the more volatile constituent evaporates first.

A. Flashing
B. Weathering
C. Inerting
D. Boiling

Answer: B — Weathering

In a multi-component cargo such as LNG, nitrogen and methane boil off preferentially. Over a voyage this weathering leaves the remaining liquid richer in heavier components like ethane and propane, raising its density and heating value.

Set 21 — 30 GASCO exit exam questions with answers

1. A gas or vapour cannot be liquefied above a particular temperature, however much pressure is applied. This temperature is called the ____ temperature.

A. adiabatic
B. critical
C. absolute
D. saturation

Answer: B — critical

Above its critical temperature a gas cannot be liquefied by pressure alone. Methane's critical temperature is about -82°C, which is why LNG must be refrigerated and carried at about -162°C rather than simply pressurised.

2. The heat which increases the temperature of an object or substance without altering its state is called ____.

A. sensible heat
B. latent heat
C. potential heat
D. radiant heat

Answer: A — sensible heat

Sensible heat changes the temperature of a substance and can be sensed with a thermometer, while the phase remains unchanged. Latent heat, by contrast, is absorbed or released during a change of state at constant temperature.

3. In the case of melting, latent heat is termed latent heat of ____.

A. vaporisation
B. fusion
C. ignition
D. sublimation

Answer: B — fusion

The heat absorbed when a solid changes to liquid at constant temperature is the latent heat of fusion. The heat absorbed when a liquid changes to vapour is the latent heat of vaporisation, which drives boil-off in LNG tanks.

4. The pressure exerted by the atmosphere at sea level is called ____ pressure.

A. absolute
B. gauge
C. atmospheric
D. partial

Answer: C — atmospheric

The weight of the air column above sea level exerts atmospheric pressure, about 1013.25 mbar. Gauge pressure is measured relative to it, and absolute pressure is the sum of gauge and atmospheric pressure.

5. Fire fighters can control an LNG pool fire by using ____.

A. a direct water jet
B. water mixed with oil
C. high-expansion foam
D. steam

Answer: C — high-expansion foam

High-expansion foam blanketing an LNG pool reduces vapour evolution and radiant heat, bringing the fire under control. Water applied directly onto LNG increases vaporisation and intensifies the fire; dry chemical powder is used for final extinguishment.

6. The best portable fire extinguisher to be used to fight a tank top fire in the engine room is the:

A. foam type
B. water type
C. dry powder type
D. soda-acid type

Answer: A — foam type

Tank top fires usually involve oil spilled in the bilges and on the tank top. Foam spreads over the burning liquid, smothering it and preventing re-ignition, whereas water would spread the oil and soda-acid is suited only to Class A fires.

7. Hazardous conditions which may result in spontaneous combustion exist when:

A. oil-soaked rags are stowed in the machine shop
B. powdered aluminium is stowed dry
C. dry metal turnings accumulate
D. paint tins are sealed and stowed in the paint locker

Answer: A — oil-soaked rags are stowed in the machine shop

Oil-soaked rags oxidise slowly, generating heat that cannot escape from a pile of material. The temperature can rise until the rags ignite on their own, so oily waste must be kept in closed metal bins and disposed of regularly.

8. What precautions must be taken in the vicinity of the engine room bilges?

A. They should be kept clear of rubbish
B. They should be covered with muck and debris
C. They should be allowed to corrode
D. They should be kept partly filled with oily water

Answer: A — They should be kept clear of rubbish

Bilges must be kept clean and free of rubbish, oil and debris. Accumulated oily waste is a fire hazard, blocks strainers and bilge suctions, and can lead to MARPOL Annex I violations if pumped overboard.

9. During loading, the vapour trapped in the space above the incoming liquid and compressed is sent to the ____.

A. compressor suction drum
B. shore tank
C. vent mast
D. engine room

Answer: B — shore tank

Incoming liquid displaces the vapour in the cargo tank. This displaced vapour is returned to the terminal through the vapour return line, using free flow or the HD compressor, so that the shore tank receives it and tank pressure stays under control.

10. The conversion of a liquid into a vapour is called ____.

A. melting
B. vaporisation
C. condensation
D. sublimation

Answer: B — vaporisation

Vaporisation is the change of state from liquid to vapour by absorbing latent heat, either by evaporation at the surface or by boiling. In LNG tanks, heat leaking through insulation causes continuous vaporisation, producing boil-off gas.

11. Vapour can be converted into the liquid state through ____.

A. melting
B. boiling
C. condensation
D. sublimation

Answer: C — condensation

Condensation is the reverse of vaporisation: a vapour gives up its latent heat and returns to liquid. Reliquefaction plants on gas carriers use this principle, compressing and cooling boil-off so it condenses and returns to the tank.

12. Methane, ethane, propane and butane are examples of ____.

A. saturated hydrocarbons
B. unsaturated hydrocarbons
C. saturated fatty acids
D. aromatic hydrocarbons

Answer: A — saturated hydrocarbons

Methane, ethane, propane and butane are alkanes, whose carbon atoms are joined only by single bonds, making them saturated hydrocarbons. Ethylene, propylene and butadiene, with double bonds, are unsaturated hydrocarbons also carried on gas carriers.

13. In the ABC method of first aid, A stands for ____.

A. Anaesthesia
B. Airway
C. Acute
D. Ambulance

Answer: B — Airway

ABC stands for Airway, Breathing and Circulation, the order in which a casualty is assessed. The airway must first be opened and kept clear, typically by head tilt and chin lift, before checking breathing and circulation.

14. Handling and storage instructions in an MSDS (SDS) will NOT include:

A. Example pictures of unsafe storage
B. Precautions for safe handling
C. Conditions for safe storage, including any incompatibilities
D. Specific end uses

Answer: A — Example pictures of unsafe storage

Section 7 of the 16-section SDS covers precautions for safe handling, conditions for safe storage including incompatibilities, and specific end uses. Pictures of unsafe storage practices are not part of the standard SDS format.

15. Which type of detector uses bimetallic strips to detect a fire?

A. Flame detectors
B. Smoke detectors
C. Heat detectors
D. Gas detectors

Answer: C — Heat detectors

Bimetallic strips bend when heated because the two metals expand at different rates, closing a contact at a set temperature or rate of rise. This is the principle of fixed-temperature and rate-of-rise heat detectors used in galleys and machinery spaces.

16. Which type of smoke detector is fitted with LEDs?

A. Photoelectric smoke detectors
B. Ionisation smoke detectors
C. Flame detectors
D. Bimetallic heat detectors

Answer: A — Photoelectric smoke detectors

Photoelectric (optical) smoke detectors use an LED light source and a photocell in a dark chamber. Smoke particles scatter or obscure the light beam, changing the photocell signal and triggering the alarm, whereas ionisation detectors use a radioactive source.

17. Methane is flammable when mixed with air in concentrations between:

A. 6% and 16%
B. 5% and 15%
C. 5% and 16%
D. 1% and 10%

Answer: B — 5% and 15%

The flammable range of methane in air is approximately 5% (lower flammable limit) to 15% (upper flammable limit) by volume. Mixtures below 5% are too lean and above 15% too rich to burn.

18. To avoid condensation in the turbine, saturated steam from the boilers is heated again using the ____.

A. heater
B. superheater
C. boiler
D. economiser

Answer: B — superheater

The superheater raises saturated steam above its saturation temperature at constant pressure. Superheated steam can expand through the turbine without condensing early, protecting blades from erosion by water droplets and improving efficiency on steam-turbine LNG carriers.

19. ____ refers to a vapour mixture which is weaker than the lower explosive limit.

A. Over-lean
B. Over-rich
C. Stoichiometric
D. Flammable

Answer: A — Over-lean

A mixture containing less hydrocarbon than the lower explosive limit is over-lean (too lean) and cannot burn. A mixture above the upper explosive limit is over-rich; only mixtures between the two limits are flammable.

20. The unit of measurement of the amount of a gas is the ____.

A. millibar
B. mole
C. gramme
D. kelvin

Answer: B — mole

The mole is the SI unit for amount of substance, containing 6.022 x 10^23 molecules. One mole of any ideal gas occupies about 22.4 litres at standard temperature and pressure, which is used in gas calculations.

21. ____ is an operating problem that happens when vapour moves rapidly over the liquid surface and liquid droplets become entrained in the vapour.

A. Flashover
B. Liquid carry-over
C. Heel
D. Rollover

Answer: B — Liquid carry-over

Liquid carry-over occurs when high vapour velocity entrains droplets into the vapour line. Liquid reaching compressors can cause severe damage, which is why demisters, knock-out drums and controlled vapour flow rates are used.

22. Ethylene carriers use:

A. Semi-pressurised and refrigerated tanks
B. Semi-pressurised and non-refrigerated tanks
C. Pressurised and non-refrigerated tanks
D. Membrane tanks at atmospheric pressure and ambient temperature

Answer: A — Semi-pressurised and refrigerated tanks

Ethylene boils at about -104°C and its critical temperature is about 9°C, so it cannot be carried fully pressurised at ambient temperature. Ethylene carriers use insulated, refrigerated, semi-pressurised Type C tanks.

23. ____ of a substance can be defined as the pressure exerted by its saturated vapour at a specific temperature.

A. Saturated vapour pressure
B. Saturated latent heat
C. Saturated vapour density
D. Critical pressure

Answer: A — Saturated vapour pressure

Saturated vapour pressure is the pressure of vapour in equilibrium with its liquid at a given temperature. It rises with temperature, which is why cargo tank pressure increases as liquefied gas warms.

24. Organs such as the ____ may be severely affected by inhalation of cold vapour.

A. liver
B. lungs
C. kidneys
D. bones

Answer: B — lungs

Inhaling very cold gas can cause cold burns to the respiratory tract and lungs. Cryogenic vapours also displace oxygen, so lung tissue damage and asphyxia are the main concerns when exposed to LNG vapour.

25. There are ____ types of flammable limits.

A. two
B. three
C. four
D. five

Answer: A — two

Flammable limits are the lower flammable limit (LFL or LEL) and the upper flammable limit (UFL or UEL). Between them lies the flammable range in which a vapour-air mixture can be ignited.

26. There are ____ sections on a Material Safety Data Sheet.

A. 16
B. 10
C. 15
D. 12

Answer: A — 16

Under the GHS format, the Safety Data Sheet has 16 standard sections, from identification and hazards through handling and storage, exposure controls, physical and chemical properties, toxicology, disposal, transport and regulatory information.

27. ____ operates by splitting air into its component gases by passing compressed air through hollow-fibre membranes.

A. Air compression process
B. Air separation process
C. Air condensing process
D. Air drying process

Answer: B — Air separation process

Membrane nitrogen generators separate air by passing it through hollow fibres; oxygen, water vapour and CO2 permeate the fibre walls faster than nitrogen, leaving a nitrogen-rich product used for inerting and purging on gas carriers.

28. ____ is defined as the temperature to which a substance must be heated for its vapour in air to ignite spontaneously without an external source.

A. Flammable range
B. Auto-ignition temperature
C. Flash point
D. Fire point

Answer: B — Auto-ignition temperature

Auto-ignition temperature is the lowest temperature at which a vapour-air mixture ignites by itself without a spark or flame. Methane's auto-ignition temperature is about 540-595°C, so hot surfaces must be controlled in gas-dangerous areas.

29. On LNG ships, when should the gas fuel supply line in the engine room be purged with inert gas?

A. Immediately before and after gas-burning operations
B. Only once a year during dry docking
C. Only after a gas leak alarm
D. Never, as it must always remain full of gas

Answer: A — Immediately before and after gas-burning operations

Purging the gas supply line with nitrogen before introducing gas prevents a flammable gas-air mixture forming, and purging after gas burning removes residual gas from the line. The IGC Code requires this inerting arrangement for the fuel gas line.

30. On an LNG ship, when should the ventilation for the machinery spaces and the gas fuel supply line ducting be operated?

A. Before and during gas-burning operations
B. Only after gas burning has stopped
C. Only when a gas alarm sounds
D. Only while the ship is in port

Answer: A — Before and during gas-burning operations

The double-walled gas pipe or ducting must be continuously ventilated and monitored before and during gas burning, so that any leakage is detected and removed. Gas supply is automatically shut off if ventilation is lost, per the IGC Code.

Set 22 — 30 GASCO exit exam questions with answers

1. Which statement about polarographic cells used for measuring the partial pressure of oxygen is correct?

A. They are temperature-sensitive and need temperature compensation
B. They are completely unaffected by temperature
C. They measure only carbon dioxide
D. They need no electrolyte or membrane

Answer: A — They are temperature-sensitive and need temperature compensation

Gas diffusion through the membrane and the electrode reaction rate both vary with temperature, so a polarographic cell's output changes with temperature. Practical analysers include a thermistor for temperature compensation.

2. Polarographic cells can be used to measure the partial pressure of oxygen in ____.

A. Both static samples and continuous gas streams
B. Static samples only
C. Liquids only
D. Gases above 50% oxygen only

Answer: A — Both static samples and continuous gas streams

Polarographic oxygen sensors respond continuously to oxygen diffusing through their membrane, so they are widely used in continuous gas-stream monitoring as well as in static or portable measurements, for example in inert gas and nitrogen systems.

3. The free surface moment of a slack rectangular cargo tank depends mainly on which dimension of the tank?

A. The cube of the tank breadth
B. The depth of liquid in the tank
C. The square of the tank length
D. The height of the tank above the keel

Answer: A — The cube of the tank breadth

The transverse free surface moment of a rectangular tank is l x b cubed / 12 multiplied by liquid density, so it varies with the cube of the breadth and is independent of the liquid depth. This is why wide slack tanks produce a large virtual loss of GM.

4. Why are fully refrigerated LPG carriers with prismatic Type A tanks normally fitted with a longitudinal centreline bulkhead inside each tank?

A. To reduce the free surface effect of the liquid cargo
B. To act as the secondary barrier
C. To support the submerged cargo pumps
D. To allow two different grades to be carried in contact

Answer: A — To reduce the free surface effect of the liquid cargo

Dividing a wide prismatic tank with a liquid-tight centreline bulkhead halves the breadth of each free surface, and because free surface moment varies with breadth cubed this greatly reduces the loss of GM. It also limits sloshing in slack conditions.

5. Under the IGC Code (2016 edition), what must every gas carrier be provided with to verify compliance with stability requirements?

A. A stability instrument capable of verifying both intact and damage stability
B. A trim and stability booklet only, without any computer
C. A shore-based stability service contract
D. A manual draught survey table

Answer: A — A stability instrument capable of verifying both intact and damage stability

IGC Code chapter 2 requires ships to be fitted with an approved stability instrument able to verify compliance with both intact and damage stability requirements, in addition to the loading and stability information booklet supplied to the master.

6. A gas carrier loads her midship cargo tanks fully while the fore and aft tanks remain empty. What stress condition is the hull most likely to experience?

A. Sagging
B. Hogging
C. Racking
D. Panting

Answer: A — Sagging

Concentrating weight amidships while the ends remain light makes the midship region sink relative to the ends, producing a sagging bending moment. Loading sequences must be planned so that shear forces and bending moments stay within permissible limits at every stage.

7. Why do large LNG carriers normally retain some water ballast even in the fully loaded condition?

A. Because the very low cargo density makes the ship volume-limited, so ballast is needed for draught, trim and stability
B. Because the IGC Code prohibits empty ballast tanks
C. To provide heat to the cargo tanks
D. To dilute any cargo leaking into the double bottom

Answer: A — Because the very low cargo density makes the ship volume-limited, so ballast is needed for draught, trim and stability

LNG has a density of only about 0.43 to 0.47 t/m3, so the cargo tanks fill by volume long before the ship reaches its deadweight. Ballast is therefore carried to achieve adequate draught, propeller immersion, trim and stability.

8. When is sloshing in a partly filled cargo tank most severe?

A. When the natural period of the liquid motion is close to the ship's period of motion
B. When the tank is almost completely full
C. When the tank is completely empty
D. When the ship is alongside in calm water

Answer: A — When the natural period of the liquid motion is close to the ship's period of motion

Sloshing impact loads become most severe when the liquid's natural period approaches the ship's rolling or pitching period, causing resonance. This is why membrane tanks have filling restrictions and why sloshing loads are considered in containment system design.

9. What must a loading or discharge plan prepared by the chief officer of a gas carrier demonstrate?

A. That stability, shear forces and bending moments remain within permissible limits at every stage of the operation
B. Only the final departure condition
C. Only the cargo quantity to be delivered
D. Only the order in which shore tanks will be used

Answer: A — That stability, shear forces and bending moments remain within permissible limits at every stage of the operation

A cargo plan must cover the sequence of cargo and ballast operations, rates and tank levels, and must show that intact stability and hull stresses remain within approved limits not only at the end but at all intermediate stages, checked on the loading instrument.

10. How do the permissible still-water shear force and bending moment values for the harbour condition generally compare with those for the seagoing condition?

A. Harbour limits are higher because no wave-induced loads are added
B. Harbour limits are lower because the ship is moored
C. Both are always identical
D. Harbour limits apply only to ballast condition

Answer: A — Harbour limits are higher because no wave-induced loads are added

Seagoing limits must leave margin for wave-induced bending and shear, so the permissible still-water values at sea are lower. In sheltered harbour conditions wave loads are small, so higher still-water values are allowed during cargo and ballast operations.

11. What is the effect of a slack cargo tank on the stability of a gas carrier?

A. It causes a virtual rise of the centre of gravity, reducing the effective GM
B. It lowers the centre of gravity, increasing GM
C. It has no effect if the cargo is a liquefied gas
D. It increases the righting lever at all angles

Answer: A — It causes a virtual rise of the centre of gravity, reducing the effective GM

Liquid moving within a slack tank shifts its centre of gravity towards the low side when the ship heels; this is treated as a virtual rise of G equal to the free surface moment divided by displacement, reducing effective GM and righting levers.

12. During loading of a gas carrier, the vessel develops an unexpected list. What should be checked first?

A. Distribution of cargo and ballast between port and starboard tanks against the loading plan
B. The calibration of the fixed gas detection system
C. The cargo compressor discharge temperature
D. The setting of the vacuum relief valves

Answer: A — Distribution of cargo and ballast between port and starboard tanks against the loading plan

An unplanned list during cargo operations normally results from unequal liquid distribution in port and starboard cargo or ballast tanks, or from a wrong valve line-up. Tank levels and ballast quantities should be compared with the plan and corrected before continuing.

13. Why should cargo and ballast operations on a gas carrier normally be carried out simultaneously in port?

A. To keep draught, trim, stability and hull stresses within limits throughout the operation
B. To reduce the boil-off rate
C. To cool the cargo pumps
D. To prevent hydrate formation in the cargo lines

Answer: A — To keep draught, trim, stability and hull stresses within limits throughout the operation

Running ballast in step with cargo transfer prevents excessive trim, list, air draught or draught changes, and keeps shear forces and bending moments within allowable values at every intermediate stage, as required by the approved loading plan.

14. Which is the main reason for avoiding intermediate filling levels in membrane LNG tanks while at sea?

A. Sloshing impact loads may damage the insulation, membrane and pump tower
B. Intermediate levels increase vapour pressure beyond MARVS
C. Intermediate levels cause the cargo to polymerise
D. Intermediate levels prevent the use of the cargo pumps

Answer: A — Sloshing impact loads may damage the insulation, membrane and pump tower

Membrane containment systems have limited resistance to sloshing impacts. Partially filled tanks at sea can experience violent liquid motion that damages the membrane, insulation boxes and pump tower, so designers specify filling restrictions that must be observed.

15. Under the IGC Code (2016), when is venting of cargo vapour to the atmosphere acceptable as a means of controlling cargo tank pressure?

A. Only in emergency situations
B. Whenever the ship is at sea beyond 12 nautical miles
C. At any time if the cargo is LNG
D. Only during loading operations

Answer: A — Only in emergency situations

IGC Code chapter 7 requires tank pressure and temperature to be kept within design limits by reliquefaction, thermal oxidation, pressure accumulation or liquid cargo cooling; venting of cargo to maintain tank pressure is not acceptable except in emergency situations.

16. Which of the following is NOT one of the methods of cargo pressure/temperature control recognised by IGC Code chapter 7?

A. Routine venting of boil-off through the vent mast
B. Reliquefaction of cargo vapours
C. Thermal oxidation of vapours, such as in a gas combustion unit or boilers
D. Pressure accumulation

Answer: A — Routine venting of boil-off through the vent mast

IGC chapter 7 lists reliquefaction, thermal oxidation, pressure accumulation and liquid cargo cooling as acceptable methods. Venting to atmosphere to control pressure is acceptable only in emergencies because it releases flammable gas and greenhouse gases.

17. Under MARPOL Annex VI regulation 12, until what date were new installations containing hydrochlorofluorocarbons (HCFCs) such as R22 permitted on ships?

A. 1 January 2020
B. 1 January 2010
C. 19 May 2005
D. 1 January 2030

Answer: A — 1 January 2020

MARPOL Annex VI prohibits new installations containing ozone-depleting substances other than HCFCs, and permitted new installations containing HCFCs, such as R22 used in older reliquefaction plants, only until 1 January 2020.

18. Which record must be maintained on board a ship having rechargeable systems that contain ozone-depleting substances, such as an R22 reliquefaction plant?

A. Ozone-depleting Substances Record Book
B. Cargo Record Book
C. Oil Record Book Part II
D. Garbage Record Book

Answer: A — Ozone-depleting Substances Record Book

MARPOL Annex VI regulation 12 requires every ship with rechargeable systems containing ozone-depleting substances to maintain an ODS Record Book, recording recharging, repairs, discharges, removal to reception facilities and supply of ODS. It may be an electronic record system.

19. Why is the refrigerant R404A sometimes used in place of R22 on gas carrier reliquefaction and air dryer plants?

A. It is an HFC with zero ozone-depleting potential, although it has a high global warming potential
B. It is non-flammable and has no global warming effect
C. It is an HCFC still freely permitted for new installations
D. It is less toxic than nitrogen

Answer: A — It is an HFC with zero ozone-depleting potential, although it has a high global warming potential

R404A is a hydrofluorocarbon blend with zero ozone-depleting potential, so it is not restricted as an ODS under MARPOL Annex VI regulation 12. However, it has a high global warming potential, so leaks must still be prevented.

20. What is meant by 'methane slip' on an LNG-fuelled or dual-fuel ship?

A. Unburnt methane escaping to atmosphere with the engine exhaust
B. Methane leaking into the secondary insulation space
C. Methane vapour returned to shore through the vapour arm
D. Loss of methane from the cargo by weathering

Answer: A — Unburnt methane escaping to atmosphere with the engine exhaust

Methane slip is unburnt methane passing through the combustion process and leaving with the exhaust, mainly in low-pressure Otto-cycle dual-fuel engines. Because methane is a powerful greenhouse gas, slip reduces the climate benefit of using LNG as fuel.

21. Why is the release of natural gas boil-off to atmosphere a particular environmental concern?

A. Methane has a global warming potential many times higher than carbon dioxide
B. Methane depletes the ozone layer
C. Methane forms acid rain directly
D. Methane is heavier than air and settles on the sea surface

Answer: A — Methane has a global warming potential many times higher than carbon dioxide

Methane is a potent greenhouse gas with a global warming potential roughly 28 to 30 times that of carbon dioxide over 100 years. Uncontrolled venting of boil-off therefore has a large climate impact and is restricted by the IGC Code to emergencies.

22. Under the BWM Convention D-2 performance standard, ballast water discharged must contain fewer than how many viable organisms per cubic metre of 50 micrometres or more in minimum dimension?

A. 10
B. 100
C. 1000
D. 50

Answer: A — 10

Regulation D-2 of the Ballast Water Management Convention requires discharge of less than 10 viable organisms per cubic metre greater than or equal to 50 micrometres, and less than 10 per millilitre between 10 and 50 micrometres, plus limits for indicator microbes.

23. Under MARPOL Annex VI, what is the maximum sulphur content of fuel oil used within an Emission Control Area for SOx?

A. 0.10% m/m
B. 0.50% m/m
C. 1.00% m/m
D. 3.50% m/m

Answer: A — 0.10% m/m

MARPOL Annex VI regulation 14 limits fuel sulphur to 0.10% m/m inside SOx Emission Control Areas and 0.50% m/m globally since 2020. Burning boil-off gas, which is practically sulphur-free, helps LNG carriers comply.

24. Under MARPOL Annex VI, the Carbon Intensity Indicator (CII) operational rating applies to which ships, including gas carriers?

A. Ships of 5,000 GT and above
B. Every ship of 400 GT and over
C. Only ships of 10,000 GT and above built after 2023
D. Only passenger ships

Answer: A — Ships of 5,000 GT and above

MARPOL Annex VI regulation 28 requires ships of 5,000 GT and above of the specified types, which include gas carriers and LNG carriers, to calculate their attained annual operational CII and receive an A to E rating each year.

25. Under MARPOL Annex VI, which emission of ozone-depleting substances from a gas carrier's refrigeration plant is prohibited?

A. Deliberate emissions, including those during maintenance, servicing, repair or disposal
B. Only emissions during cargo loading
C. Only emissions within 12 nautical miles of land
D. Only emissions exceeding 10 kg per year

Answer: A — Deliberate emissions, including those during maintenance, servicing, repair or disposal

MARPOL Annex VI regulation 12 prohibits any deliberate emissions of ozone-depleting substances, including emissions occurring while maintaining, servicing, repairing or disposing of systems. Minimal releases associated with recapture or recycling are not deliberate emissions.

26. What is the maximum oil content permitted in machinery-space bilge water discharged at sea from a gas carrier outside special areas under MARPOL Annex I?

A. 15 ppm
B. 100 ppm
C. 30 litres per nautical mile
D. 5 ppm

Answer: A — 15 ppm

MARPOL Annex I regulation 15 allows machinery-space bilge discharge only when the ship is en route, through approved oil filtering equipment, with oil content not exceeding 15 ppm. This applies to gas carriers as to all ships of 400 GT and above.

27. Why must copper, brass and zinc-containing materials not be used in cargo systems for ammonia?

A. Ammonia attacks copper, copper alloys and zinc
B. Ammonia makes these metals brittle at low temperature only
C. These metals catalyse ammonia polymerisation
D. They generate static electricity with ammonia

Answer: A — Ammonia attacks copper, copper alloys and zinc

Ammonia is corrosive to copper, copper alloys and zinc, including galvanised surfaces. The IGC Code therefore excludes these materials from cargo tanks, piping, valves and fittings in contact with ammonia liquid or vapour.

28. Which measure helps minimise stress corrosion cracking of carbon-manganese steel cargo tanks carrying anhydrous ammonia?

A. Keeping a small water content in the ammonia and minimising oxygen in the tank vapour
B. Adding mercury to the ammonia
C. Carrying the ammonia at the highest possible temperature
D. Using compressed air to pad the tank

Answer: A — Keeping a small water content in the ammonia and minimising oxygen in the tank vapour

Stress corrosion cracking in carbon-manganese steel is promoted by oxygen contamination of ammonia. The IGC Code precautions include keeping oxygen in the vapour space very low and maintaining a small water content in the ammonia, which acts as an inhibitor.

29. Under the IGC Code, which information must the inhibitor certificate for an inhibited cargo provide?

A. Name and amount of inhibitor, date added, expected lifetime, any temperature limitations and action if the voyage exceeds the inhibitor life
B. Only the trade name of the inhibitor
C. Only the cargo's boiling point and density
D. Only the shipper's address

Answer: A — Name and amount of inhibitor, date added, expected lifetime, any temperature limitations and action if the voyage exceeds the inhibitor life

For cargoes required to be inhibited, the IGC Code requires a certificate from the manufacturer stating the inhibitor name and amount, date added, expected duration of effectiveness, temperature limitations and the action to be taken if the voyage exceeds the effective lifetime.

30. Why must oxygen be kept to a very low level in tanks carrying butadiene?

A. Butadiene reacts with oxygen to form unstable peroxides that can initiate polymerisation
B. Oxygen makes butadiene non-flammable
C. Oxygen raises the boiling point of butadiene above ambient
D. Oxygen reacts with the inhibitor to form hydrates

Answer: A — Butadiene reacts with oxygen to form unstable peroxides that can initiate polymerisation

Butadiene reacts with oxygen to form unstable peroxides, which are explosive and can trigger uncontrolled polymerisation. Cargo tanks are therefore inerted to a very low oxygen content and the cargo is inhibited before shipment.

Set 23 — 30 GASCO exit exam questions with answers

1. Normal butane and isobutane have the same chemical formula, C4H10, but different molecular structures. They are called:

A. Isomers
B. Isotopes
C. Polymers
D. Allotropes

Answer: A — Isomers

Isomers are compounds with the same molecular formula but different structural arrangements. Normal butane has a straight carbon chain while isobutane is branched, which gives them different boiling points and vapour pressures.

2. What is the chemical formula of propylene?

A. C3H6
B. C3H8
C. C2H4
D. C4H6

Answer: A — C3H6

Propylene (propene) is an unsaturated hydrocarbon with one carbon-carbon double bond and the formula C3H6. Propane is C3H8, ethylene C2H4 and butadiene C4H6.

3. Which of the following liquefied gas cargoes is a saturated hydrocarbon?

A. Propane
B. Ethylene
C. Propylene
D. Butadiene

Answer: A — Propane

Saturated hydrocarbons (alkanes) contain only single carbon-carbon bonds; propane is an alkane. Ethylene, propylene and butadiene contain double bonds, making them unsaturated and more chemically reactive.

4. Why must the temperature of an inhibited cargo such as butadiene or vinyl chloride monomer be kept as low as practicable during the voyage?

A. Polymerisation is accelerated at higher temperature and the inhibitor is depleted faster
B. Higher temperature makes the cargo freeze
C. Higher temperature converts the cargo to hydrates
D. Higher temperature makes the cargo non-flammable

Answer: A — Polymerisation is accelerated at higher temperature and the inhibitor is depleted faster

Polymerisation is exothermic and its rate rises with temperature, while the inhibitor is consumed more quickly. Keeping the cargo cool extends the inhibitor's effective life, which is why the inhibitor certificate may state temperature limits.

5. Why is a water spray or water curtain effective in reducing an ammonia vapour cloud?

A. Ammonia is highly soluble in water
B. Ammonia reacts with water to form an inert gas
C. Water raises ammonia's flash point
D. Water freezes ammonia into solid hydrates

Answer: A — Ammonia is highly soluble in water

Ammonia is extremely soluble in water, so a water spray absorbs a large amount of vapour and helps knock down a toxic cloud. Large quantities of water must be used, as the dissolution releases heat and the run-off is alkaline.

6. Under IGC Code chapter 19, which ship type is required for the carriage of chlorine?

A. Type 1G
B. Type 2G
C. Type 2PG
D. Type 3G

Answer: A — Type 1G

Chlorine is highly toxic and is assigned to ship type 1G in the IGC Code summary of minimum requirements, with independent Type C tanks and additional special requirements, because it presents the most severe hazards.

7. Before loading a cargo, compatibility must be checked between the cargo and which of the following?

A. Materials of construction, previous cargo residues, other cargoes carried and the refrigerant of the reliquefaction plant
B. Only the paint on the deck
C. Only the ship's fuel oil
D. Only the lifeboat equipment

Answer: A — Materials of construction, previous cargo residues, other cargoes carried and the refrigerant of the reliquefaction plant

Liquefied gases may react with tank and seal materials, previous cargo residues, adjacent cargoes or the refrigerant if a condenser leaks. Chemical data sheets, compatibility charts and the IGC Code requirements are used to confirm compatibility before loading.

8. Mixing which two cargoes, if carried on the same ship, would require completely separate cargo handling and reliquefaction systems because they react dangerously?

A. Ammonia and chlorine
B. Propane and butane
C. Methane and ethane
D. Propane and propylene

Answer: A — Ammonia and chlorine

Ammonia and chlorine react violently, so segregation requires separate piping, vent and reliquefaction systems. Propane, butane, methane, ethane and propylene are compatible hydrocarbons that may share common systems with appropriate grade separation.

9. Which industry publication provides guidance for ship-to-ship transfer of liquefied gases together with petroleum and chemicals?

A. Ship to Ship Transfer Guide for Petroleum, Chemicals and Liquefied Gases (ICS, OCIMF, SIGTTO, CDI)
B. International Code of Signals
C. IMDG Code
D. Bridge Procedures Guide

Answer: A — Ship to Ship Transfer Guide for Petroleum, Chemicals and Liquefied Gases (ICS, OCIMF, SIGTTO, CDI)

The joint ICS, OCIMF, SIGTTO and CDI Ship to Ship Transfer Guide for Petroleum, Chemicals and Liquefied Gases covers planning, risk assessment, equipment, mooring, communications and emergency procedures for STS operations, including liquefied gas cargoes.

10. In an STS transfer at sea, which ship normally maintains a steady course and speed while the other manoeuvres alongside?

A. The constant heading ship, usually the larger vessel
B. The manoeuvring ship, usually the larger vessel
C. Neither ship; both must stop engines
D. The ship with the most cargo remaining

Answer: A — The constant heading ship, usually the larger vessel

In an underway STS approach the constant heading ship keeps a steady heading, usually at slow speed, while the manoeuvring ship, normally the smaller vessel, approaches and berths alongside. Roles are agreed in advance in the STS plan.

11. What type of primary fenders is most commonly used between two ships during an STS operation?

A. Large floating pneumatic (Yokohama-type) fenders
B. Wooden fender boards
C. Old tyres tied to the rails
D. Rope fenders

Answer: A — Large floating pneumatic (Yokohama-type) fenders

Floating pneumatic fenders are used as primary fenders in STS operations because they absorb large berthing energies with low reaction force. Their number and size are selected according to the ships' displacements and approach conditions.

12. In an STS operation, what is the role of the 'Person in Overall Advisory Control' (POAC)?

A. To advise and coordinate the whole STS operation, without relieving the masters of their responsibility
B. To take command of both ships
C. To act as cargo surveyor for custody transfer
D. To represent the port state control authority

Answer: A — To advise and coordinate the whole STS operation, without relieving the masters of their responsibility

The STS guide defines the POAC as the person who provides advice and coordination for the entire STS operation. Each master nevertheless retains full responsibility for the safety of his ship, crew, cargo and the environment.

13. In the Ship/Shore Safety Checklist, what does the code 'R' against an item indicate?

A. The item must be re-checked at the intervals agreed and stated in the declaration
B. The item has been rejected
C. The item applies only to refrigerated cargo
D. The item is the responsibility of the shore only

Answer: A — The item must be re-checked at the intervals agreed and stated in the declaration

In the ISGOTT-based Ship/Shore Safety Checklist, 'R' marks items that are to be re-checked at agreed intervals during the operation. 'A' indicates an agreement or procedure to be identified, and 'P' indicates that permission is to be granted.

14. What is the purpose of an insulating flange fitted in the terminal loading arm or hose string?

A. To prevent stray electrical currents flowing between ship and shore and causing arcing at the manifold
B. To insulate the cargo from heat ingress
C. To act as an emergency release coupling
D. To allow nitrogen purging of the arm

Answer: A — To prevent stray electrical currents flowing between ship and shore and causing arcing at the manifold

An insulating flange interrupts electrical continuity between ship and shore, preventing stray currents, such as from cathodic protection, from causing incendive sparks when arms or hoses are connected or disconnected. A ship-shore bonding cable is not a substitute.

15. Which items must be agreed between ship and terminal at the pre-transfer meeting before liquefied gas cargo operations begin?

A. Transfer rates, ESD procedures and signals, communications, emergency procedures and vapour return arrangements
B. Only the date of departure
C. Only the agent's fees
D. Only the crew list

Answer: A — Transfer rates, ESD procedures and signals, communications, emergency procedures and vapour return arrangements

The pre-transfer conference covers cargo quantities, sequence and maximum rates, vapour handling, ESD and emergency release procedures, communications and language, emergency signals and the checklist items. Agreement is recorded in the Ship/Shore Safety Checklist.

16. Why must a gas carrier be checked for compatibility with a terminal before first arrival?

A. To confirm that mooring, manifold, loading arm envelope, ESD link and gangway arrangements match the berth
B. To confirm the crew's nationality
C. To agree the freight rate
D. To check the ship's paint scheme

Answer: A — To confirm that mooring, manifold, loading arm envelope, ESD link and gangway arrangements match the berth

A ship/shore compatibility study verifies that the ship's size, mooring arrangement, manifold position and flange sizes, loading arm operating envelope, ESD and communication links and access arrangements are suitable for the terminal before the first call.

17. During STS transfer of liquefied gas, what is required for cargo hoses between the two ships?

A. Hoses must be suitable for the cargo and temperature, tested and certified, and supported so that their minimum bend radius is not exceeded
B. Any hose of the correct diameter may be used
C. Hoses need not be tested if new
D. Hoses should be left unsupported to allow free movement

Answer: A — Hoses must be suitable for the cargo and temperature, tested and certified, and supported so that their minimum bend radius is not exceeded

STS guidance requires hoses designed for the cargo and its temperature and pressure, with valid test certificates, and proper support so that the minimum bend radius is not exceeded as the ships move relative to each other.

18. Which condition would normally require an STS transfer of liquefied gas to be stopped and hoses disconnected?

A. Weather or sea conditions exceeding the limits agreed in the STS plan
B. Arrival of a provisions boat at the other ship
C. Change of watch on either ship
D. Completion of one tank in the sequence

Answer: A — Weather or sea conditions exceeding the limits agreed in the STS plan

STS plans set limits for wind, sea state and relative ship motion. If these are exceeded, or if an emergency, loss of communication or a cargo leak occurs, transfer must be stopped, lines drained and hoses disconnected so that the ships can separate safely.

19. Under the IGC Code, a type 2PG ship is one of 150 m in length or less that carries products in which type of cargo tank?

A. Independent type C tanks with MARVS of at least 0.7 MPa gauge and design temperature of -55°C or above
B. Membrane tanks with MARVS not exceeding 0.025 MPa gauge
C. Independent type A tanks designed for -163°C
D. Integral tanks forming part of the hull structure

Answer: A — Independent type C tanks with MARVS of at least 0.7 MPa gauge and design temperature of -55°C or above

The IGC Code defines a type 2PG ship as a gas carrier of 150 m or less carrying ship type 2G products in independent type C tanks designed for a MARVS of at least 0.7 MPa gauge and a cargo containment design temperature of -55°C or above.

20. Which cargo is required by chapter 19 of the IGC Code to be carried only in a type 1G ship?

A. Chlorine
B. Propane
C. Butane
D. Methane (LNG)

Answer: A — Chlorine

Chlorine is highly toxic and corrosive, so the IGC Code chapter 19 summary of minimum requirements assigns it to ship type 1G in independent type C tanks, with maximum preventive measures against escape of cargo. LPG and LNG are carried in type 2G ships.

21. A fully refrigerated LPG carrier typically carries its cargo in which condition?

A. At about atmospheric pressure and at or near its boiling point, down to about -50°C
B. At ambient temperature under pressures up to about 18 bar
C. At -163°C in membrane tanks
D. At about 5 to 8 bar and -10°C in spherical tanks

Answer: A — At about atmospheric pressure and at or near its boiling point, down to about -50°C

Fully refrigerated LPG ships carry propane, butane, ammonia and similar cargoes at near atmospheric pressure, cooled to their atmospheric boiling points (propane about -42°C), usually in independent type A prismatic tanks with a reliquefaction plant controlling tank pressure.

22. Why are ethylene carriers normally of the semi-pressurised/fully refrigerated type with a cascade reliquefaction plant?

A. Ethylene boils at about -104°C at atmospheric pressure and has a low critical temperature, so it cannot be liquefied by pressure alone at ambient temperature
B. Ethylene is heavier than LPG and needs stronger tanks
C. Ethylene must be carried at -163°C like LNG
D. Ethylene polymerises if carried under refrigeration

Answer: A — Ethylene boils at about -104°C at atmospheric pressure and has a low critical temperature, so it cannot be liquefied by pressure alone at ambient temperature

Ethylene has an atmospheric boiling point of about -104°C and a critical temperature of about +9.5°C, so it must be refrigerated. A cascade cycle using a secondary refrigerant such as R-1270 or R-404A is needed to condense ethylene vapour at such low temperatures.

23. What is the principal function of a Floating Storage and Regasification Unit (FSRU)?

A. To receive and store LNG and convert it back to gas on board for send-out to a shore pipeline
B. To liquefy natural gas from offshore wells
C. To act as a bunker barge supplying LPG to ships
D. To carry compressed natural gas in cylinders

Answer: A — To receive and store LNG and convert it back to gas on board for send-out to a shore pipeline

An FSRU stores LNG delivered by carriers and regasifies it using on-board vaporisers heated by seawater or another medium, sending high-pressure natural gas ashore through a pipeline. It provides a quicker, cheaper import terminal than a land-based regasification plant.

24. According to the IGC Code, entrances and openings to accommodation spaces on the side boundaries of a deckhouse must be located how far from the end facing the cargo area?

A. At least L/25, but not less than 3 m, which need not exceed 5 m
B. At least 10 m in all cases
C. At least B/3 or 6 m, whichever is greater
D. At least 1.5 m

Answer: A — At least L/25, but not less than 3 m, which need not exceed 5 m

IGC Code chapter 3 requires entrances, air inlets and openings to accommodation, service and machinery spaces and control stations not to face the cargo area; on the side boundaries they must be at least L/25 (minimum 3 m, need not exceed 5 m) from the end facing the cargo area.

25. What is the main advantage of a semi-pressurised/semi-refrigerated gas carrier over a fully pressurised ship?

A. Reduced tank wall thickness and weight, allowing larger cargo capacity, while still able to load from pressurised or refrigerated terminals
B. It needs no reliquefaction plant
C. It can carry LNG at -163°C
D. It does not require any secondary barrier or insulation for any cargo

Answer: A — Reduced tank wall thickness and weight, allowing larger cargo capacity, while still able to load from pressurised or refrigerated terminals

By partly refrigerating the cargo, semi-pressurised ships use type C tanks designed for lower pressures (typically 5 to 8 bar), so tanks are lighter and larger. Their reliquefaction plant and insulation give flexibility to load and discharge at both pressurised and refrigerated terminals.

26. Traditionally, why were steam turbines used on LNG carriers?

A. Boilers could burn the boil-off gas together with fuel oil in any proportion, disposing of BOG safely
B. Steam turbines were cheaper to run than diesel engines
C. Diesel engines were prohibited on gas carriers
D. Steam was needed to keep the cargo warm

Answer: A — Boilers could burn the boil-off gas together with fuel oil in any proportion, disposing of BOG safely

Steam plant boilers can fire natural boil-off gas, fuel oil or both, so BOG from the cargo tanks could be used as fuel without a reliquefaction plant. Their poor thermal efficiency later led to DFDE, slow-speed dual-fuel engines and reliquefaction systems.

27. Under the IGC Code, how many pressure relief valves must be fitted to a cargo tank with a volume of more than 20 m³?

A. At least two of approximately equal capacity
B. At least one
C. At least three, one of which is spring-loaded
D. At least four, two for pressure and two for vacuum

Answer: A — At least two of approximately equal capacity

IGC Code chapter 8 requires each cargo tank above 20 m³ to have at least two pressure relief valves of approximately equal capacity, so that one can be taken out of service while the other still protects the tank. Tanks of 20 m³ or less may have one.

28. What is the minimum required height of a cargo tank vent outlet above the weather deck according to the IGC Code?

A. B/3 or 6 m, whichever is greater
B. 2.4 m
C. B/15 or 2 m, whichever is less
D. 10 m in all cases

Answer: A — B/3 or 6 m, whichever is greater

Vent outlets from pressure relief valves must be at least B/3 or 6 m above the weather deck, whichever is greater, and 6 m above the working area and fore-and-aft gangway, so that released vapour disperses clear of personnel.

29. Cargo vent outlets must be arranged at a distance from the nearest air intake or opening to accommodation, service and machinery spaces of at least:

A. B or 25 m, whichever is less
B. 5 m
C. L/25
D. 50 m, whichever is greater

Answer: A — B or 25 m, whichever is less

The IGC Code requires pressure relief vent outlets to be at least B or 25 m, whichever is less, from the nearest air intake, outlet or opening to accommodation, service and machinery spaces and other gas-safe spaces, to stop vapour entering them.

30. When alternative (harbour) pressure relief valve settings are used, which requirement applies?

A. Changes are made under the Master's supervision per approved procedures, recorded in the log, and the set pressure is displayed at the cargo control station and at each relief valve
B. The chief officer may change settings by adjusting springs without recording
C. Settings may be raised above MARVS while in port
D. No requirement, as harbour settings are optional

Answer: A — Changes are made under the Master's supervision per approved procedures, recorded in the log, and the set pressure is displayed at the cargo control station and at each relief valve

IGC Code chapter 8 allows more than one relief valve setting only under the Master's supervision, following procedures in the cargo operations manual. The change must be recorded in the ship's log and a sign showing the set pressure posted at the cargo control station and at each valve.

Set 24 — 20 GASCO exit exam questions with answers

1. Cargo tank pressure relief valves on gas carriers are sized primarily for which design case?

A. Fire exposure of the tank, plus vapour from purging or other sources
B. Normal boil-off at sea
C. Maximum loading rate only
D. Thermal expansion of liquid in the lines

Answer: A — Fire exposure of the tank, plus vapour from purging or other sources

The IGC Code bases required relief capacity mainly on the vapour generated when the tank is exposed to fire, using a formula that relates flow to the tank's external surface area, latent heat and insulation. This governs the size of valves and vent risers.

2. Apart from relief valves, what does the IGC Code require for a cargo tank not designed to withstand the maximum external pressure difference?

A. Two independent pressure switches to alarm and then stop suction of liquid or vapour from the tank, or vacuum relief valves
B. A gas-freeing fan permanently connected
C. A second spool piece at the manifold
D. A water spray nozzle inside the tank

Answer: A — Two independent pressure switches to alarm and then stop suction of liquid or vapour from the tank, or vacuum relief valves

Where tanks could be damaged by vacuum, IGC Code 8.4 requires vacuum protection, such as two independent pressure switches that first alarm and then stop all suction from the tank, or vacuum relief valves admitting inert gas, cargo vapour or air.

3. What is the main advantage of a pilot-operated relief valve over a simple spring-loaded valve on a low-pressure cargo tank?

A. It stays tight close to its set pressure and opens fully with little overpressure, giving accurate settings at low pressures
B. It does not need to be tested or maintained
C. It can only lift when the vent mast is on fire
D. It can be set above MARVS

Answer: A — It stays tight close to its set pressure and opens fully with little overpressure, giving accurate settings at low pressures

In a pilot-operated valve, a small pilot senses tank pressure and controls a large main valve. It stays tight up to near set pressure and opens fully with minimal overpressure, which suits the low MARVS of membrane and type A or B tanks.

4. What is the purpose of the nitrogen purging/snuffing connection at the top of an LNG carrier's vent mast?

A. To extinguish a fire at the vent outlet caused by ignited vented vapour
B. To raise tank pressure during discharge
C. To dry the cargo tanks before loading
D. To supply nitrogen to the insulation spaces

Answer: A — To extinguish a fire at the vent outlet caused by ignited vented vapour

If vapour released through the vent riser is ignited, e.g. by lightning, nitrogen injected into the mast smothers the flame at the outlet. Vent masts are also kept free of water and debris so relief valves can discharge freely.

5. Under IGC Code chapter 18, the closing time of ESD valves at the manifold, measured from activation to final closure, must normally not exceed:

A. 30 seconds
B. 5 seconds
C. 2 minutes
D. 5 minutes

Answer: A — 30 seconds

IGC Code 18.10 requires manifold ESD valves to close fully within 30 seconds of activation. The closing time must be known and compatible with the shore system so that loading rates can be set to avoid unacceptable surge pressures in the hoses or arms.

6. To avoid surge pressure, how does the IGC Code relate the maximum loading rate to the ESD valve closing time?

A. Loading rate in m³/h should not exceed 3600 U/t, where U is the ullage volume at the operating signal level and t the time to stop flow
B. Loading rate should equal the shore pump capacity
C. Loading rate should be reduced only when topping off the last tank
D. There is no relationship; closing time is fixed

Answer: A — Loading rate in m³/h should not exceed 3600 U/t, where U is the ullage volume at the operating signal level and t the time to stop flow

IGC Code 18.10 gives the maximum loading rate as LR = 3600 U/t m³/h. U is the ullage volume at the level that triggers the ESD signal, and t is the time in seconds from that signal to full valve closure, so the tank cannot overfill while the valves close.

7. In SIGTTO terminology, what distinguishes ESD-2 from ESD-1 on a loading arm system?

A. ESD-2 activates the powered emergency release coupling to separate the arms, after ESD-1 has stopped the transfer
B. ESD-2 only sounds an alarm
C. ESD-2 restarts the cargo pumps
D. ESD-2 opens the manifold valves

Answer: A — ESD-2 activates the powered emergency release coupling to separate the arms, after ESD-1 has stopped the transfer

ESD-1 stops cargo pumps and closes ESD valves to halt transfer. ESD-2, triggered for example by the ship moving beyond the arm envelope, operates the emergency release system: double valves close and the coupling releases, letting the ship separate with minimal spillage.

8. What is the key safety feature of an emergency release coupling (ERC) on a liquefied gas loading arm?

A. Two valves close either side of the coupling before it separates, so only a small amount of liquid is released
B. It cuts the arm with a hydraulic blade
C. It allows the arm to stretch to follow the ship
D. It vents the arm contents to atmosphere before release

Answer: A — Two valves close either side of the coupling before it separates, so only a small amount of liquid is released

An ERC (or PERC) is a dry-break device: interlocked ball or butterfly valves on each side of the coupling close first, then the coupling separates. Only the small volume trapped between the valves is released, protecting people and structure from cryogenic spills.

9. When should the ship-shore ESD link be tested during a cargo port call?

A. After connection and before cargo transfer starts, as agreed at the pre-transfer meeting
B. Only during dry-dock
C. Only after discharge is complete
D. Only if a leak has occurred

Answer: A — After connection and before cargo transfer starts, as agreed at the pre-transfer meeting

Ship/shore safety checklists and SIGTTO guidance require the ship-to-shore and shore-to-ship ESD functions to be tested once the link is connected and before transfer begins. This confirms both sides will stop cargo flow when either activates its ESD.

10. Why is a fibre-optic ship-shore link often preferred to an electrical link at LNG terminals?

A. It can also carry telephone and data signals, is immune to electrical interference and carries no spark hazard
B. It does not need a connector at the manifold
C. It works without any shore equipment
D. It replaces the need for ESD valves

Answer: A — It can also carry telephone and data signals, is immune to electrical interference and carries no spark hazard

Fibre-optic links carry ESD signals plus hotline telephone, mooring-load and data channels over one cable. As light rather than current carries the signal, they do not suffer electromagnetic interference and pose no ignition risk in the hazardous manifold area.

11. What happens to the ship's ESD system if electrical or control-air power to it is lost?

A. It is designed to fail safe, closing the ESD valves and stopping cargo transfer
B. The valves stay in their last position until power returns
C. Only an alarm is given and transfer continues
D. The cargo pumps speed up to finish quickly

Answer: A — It is designed to fail safe, closing the ESD valves and stopping cargo transfer

ESD systems are fail-safe: loss of control power or instrument air closes the ESD valves and trips cargo pumps and compressors. A component failure therefore stops transfer rather than leaving the transfer running without emergency protection.

12. During a planned stop, why should cargo flow be reduced and shore pumps stopped before ESD valves are closed?

A. To prevent surge pressure from rapid valve closure against a full-rate flow
B. To allow the ESD link to be disconnected faster
C. To increase the boil-off rate
D. To warm up the manifold

Answer: A — To prevent surge pressure from rapid valve closure against a full-rate flow

Closing a valve rapidly against full-rate liquid flow creates a pressure surge (liquid hammer) that can burst hoses, arms or piping. ESD valves are an emergency device; normal stops should be by reducing rate and stopping pumps first.

13. When gassing-up a cargo tank with methane vapour after inerting, how is the vapour introduced and the inert gas removed?

A. Warm methane vapour is introduced at the tank top and the heavier inert gas is pushed out through the bottom filling line
B. Methane is introduced at the bottom and inert gas vented from the top
C. Liquid LNG is sprayed in at full rate with all vents closed
D. Inert gas and methane are mixed by the tank fans

Answer: A — Warm methane vapour is introduced at the tank top and the heavier inert gas is pushed out through the bottom filling line

Methane is lighter than inert gas, so it is introduced at the top and the heavier inert gas is displaced from the bottom by a piston effect, mixing as little as possible. For heavier vapours like propane the process is reversed.

14. Why must inert gas from a combustion-type generator be replaced by cargo vapour before LNG cool-down?

A. Its carbon dioxide would freeze at LNG temperatures, forming solids that can damage pumps and block valves and spray nozzles
B. Inert gas reacts violently with LNG
C. Inert gas makes the cargo off-spec only for odour
D. Inert gas raises the boiling point of LNG

Answer: A — Its carbon dioxide would freeze at LNG temperatures, forming solids that can damage pumps and block valves and spray nozzles

Combustion inert gas contains about 14% CO2, which solidifies at about -78°C. At LNG temperatures it would form dry ice that blocks lines, sprays and pump inlets, so tanks are gassed up with LNG vapour before cooling down.

15. To what dew point should cargo tanks be dried before loading a refrigerated cargo?

A. Below the lowest temperature the tank and cargo system will reach in service
B. Equal to ambient seawater temperature
C. 0°C in all cases
D. Above the cargo boiling point

Answer: A — Below the lowest temperature the tank and cargo system will reach in service

If moisture remains when the tank is cooled below its dew point, water condenses and freezes. The resulting ice and hydrates can block pumps, valves and instrument lines, so tanks are dried with dry air or nitrogen until the dew point is below the lowest expected system temperature.

16. During the warming-up of LNG cargo tanks before gas freeing, how is the heat normally supplied?

A. Cargo vapour is heated in the cargo heater and circulated to the tanks by the compressor
B. Steam is injected directly into the tanks
C. Seawater is pumped into the hold spaces
D. The tanks are left open to atmosphere

Answer: A — Cargo vapour is heated in the cargo heater and circulated to the tanks by the compressor

Warm-up uses a closed cycle: cold vapour is drawn from the tanks by the high-duty compressor, heated in the cargo heater and returned to the tank bottoms. This evaporates residual liquid and raises the temperature before inerting and aeration.

17. Why are cargo tanks inerted after warming up and before aeration with dry air?

A. To lower the hydrocarbon content so that the tank atmosphere does not pass through the flammable range when air is introduced
B. To cool the tanks again
C. To increase the oxygen content
D. To prevent the cargo heater from overheating

Answer: A — To lower the hydrocarbon content so that the tank atmosphere does not pass through the flammable range when air is introduced

Admitting air directly to a tank full of hydrocarbon vapour would create a flammable mixture. Inert gas or nitrogen first displaces the vapour until the hydrocarbon content is low enough that adding air will not bring the mixture into the flammable range.

18. Why is the loading rate reduced during topping-off of cargo tanks?

A. To control the final level accurately and avoid exceeding the permitted filling limit or triggering high-level ESD
B. To increase the boil-off rate
C. To allow the tank to warm up
D. To save shore pump power

Answer: A — To control the final level accurately and avoid exceeding the permitted filling limit or triggering high-level ESD

As tanks approach their filling limits, rates are reduced in agreement with the terminal so levels can be monitored and valves closed in time. This avoids overfilling past the IGC Code filling limit and unplanned high-level shutdowns causing surge.

19. On a laden LNG voyage, which parameters must be continuously monitored as part of care of cargo in transit?

A. Tank pressures, cargo temperatures, levels and the operation of the BOG handling system
B. Only the ballast tank soundings
C. Only the manifold pressure
D. Only the cargo pump motor insulation

Answer: A — Tank pressures, cargo temperatures, levels and the operation of the BOG handling system

In transit, heat ingress produces boil-off that must be consumed as fuel, reliquefied or burnt in the GCU to keep tank pressure within limits. Watchkeepers monitor tank pressures, temperatures, levels, cofferdam and insulation space conditions and gas detection.

20. During bulk loading of LNG at a terminal, how is cargo tank pressure normally controlled?

A. Displaced vapour and flash gas are returned to shore through the vapour return line, using the high-duty compressor if needed
B. Vapour is vented continuously through the vent mast
C. The loading rate is kept at maximum and pressure ignored
D. Tank pressure is controlled by opening the insulation space relief valves

Answer: A — Displaced vapour and flash gas are returned to shore through the vapour return line, using the high-duty compressor if needed

Incoming liquid displaces vapour and flashes as it enters the warmer tanks. The vapour is sent back to the terminal through the vapour return line, boosted by the HD compressor when tank pressure rises, keeping pressure well below relief settings without venting.

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Practise these GASCO questions as a timed paper GASCO exit exam sets and syllabus All 24 STCW exit exam courses

GASCO exit exam questions and answers — Advanced Training for Liquefied Gas Tanker Cargo Operations

Set 1 — 30 GASCO exit exam questions with answers · as grouped in the bank

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Set 10 — 30 GASCO exit exam questions with answers · as grouped in the bank

Set 11 — 30 GASCO exit exam questions with answers · as grouped in the bank

Set 12 — 30 GASCO exit exam questions with answers · as grouped in the bank

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Set 18 — 30 GASCO exit exam questions with answers · as grouped in the bank

Set 19 — 30 GASCO exit exam questions with answers · as grouped in the bank

Set 20 — 30 GASCO exit exam questions with answers · as grouped in the bank

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Set 1 — 30 GASCO exit exam questions with answers

Set 2 — 30 GASCO exit exam questions with answers

Set 3 — 30 GASCO exit exam questions with answers

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Set 10 — 30 GASCO exit exam questions with answers

Set 11 — 30 GASCO exit exam questions with answers

Set 12 — 30 GASCO exit exam questions with answers

Set 13 — 30 GASCO exit exam questions with answers

Set 14 — 30 GASCO exit exam questions with answers

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Set 18 — 30 GASCO exit exam questions with answers

Set 19 — 30 GASCO exit exam questions with answers

Set 20 — 30 GASCO exit exam questions with answers

Set 21 — 30 GASCO exit exam questions with answers

Set 22 — 30 GASCO exit exam questions with answers

Set 23 — 30 GASCO exit exam questions with answers

Set 24 — 20 GASCO exit exam questions with answers