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GASCO exit exam questions and answers — Set 19 — Advanced Training for Liquefied Gas Tanker Cargo Operations

Set 19 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.

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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.

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