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GASCO exit exam questions and answers — Set 20 — Advanced Training for Liquefied Gas Tanker Cargo Operations

Set 20 of the Advanced Training for Liquefied Gas Tanker Cargo Operations (GASCO) exit exam bank — 30 of 710 questions, 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.

These are the bank's original groupings. Practising deals the whole bank out again every time you reshuffle, so a practice “Set 3” is a different 30 questions each time — the set numbers below are the source file's, and are only used here so the key stays navigable. Options are listed in their original order with fixed letters; when you practise, those move too.

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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.

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