LGTCO/LGTF exit exam questions and answers — Set 20 — Liquefied Gas Tanker Cargo Operations

Set 20 of the Liquefied Gas Tanker Cargo Operations (LGTCO/LGTF) exit exam bank — 29 of 599 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 20 — 29 LGTCO/LGTF exit exam questions with answers

1. In LNG ships, the LOW-DUTY compressor handles boil-off gas during…

A. the loaded and ballast voyage — sending BOG to the engine room as fuel
B. cool-down of the cargo tanks
C. tank inerting
D. gas-freeing before dry dock

Answer: A — the loaded and ballast voyage — sending BOG to the engine room as fuel

The low-duty compressor delivers natural boil-off gas to the boilers or dual-fuel engines as fuel throughout the sea passage. The much larger vapour flows during loading and cool-down are handled by the HIGH-duty compressor.

2. What does 'TWA' stand for?

A. Total Weighted Allowance
B. Toxic Working Amount
C. Time-Weighted Average
D. Threshold Warning Alarm

Answer: C — Time-Weighted Average

TWA is the Time-Weighted Average — the average airborne concentration a worker may be exposed to over a normal 8-hour day. It is paired with the STEL, the 15-minute short-term limit; ammonia, for example, has a TWA of 25 ppm.

3. The refrigerant 'Freon' is…

A. a flammable hydrocarbon refrigerant
B. a non-flammable halocarbon refrigerant used in cascade plants and air driers
C. an inert gas used for purging
D. a foam-forming fire-fighting agent

Answer: B — a non-flammable halocarbon refrigerant used in cascade plants and air driers

'Freon' is a family of non-flammable halocarbon refrigerants. It is the working fluid in the secondary loop of a cascade reliquefaction plant and in refrigerated air driers — it never comes into contact with the cargo itself.

4. TRUE or FALSE: thunderstorms with lightning present no danger during tanker cargo operations.

A. TRUE — cargo operations may continue normally
B. TRUE, provided the deck is wetted down
C. TRUE, provided the vessel is earthed to the jetty
D. FALSE — cargo operations must be STOPPED and all openings closed

Answer: D — FALSE — cargo operations must be STOPPED and all openings closed

The statement is false. Lightning is an ignition source, so cargo transfer, tank venting and gauging are stopped and all openings closed until the storm passes. Read the stem carefully — it is deliberately written in the affirmative as a trap.

5. Dry powder systems use nitrogen or carbon dioxide as a…

A. cooling agent
B. propellant to expel the powder
C. chemical inhibitor
D. wetting agent

Answer: B — propellant to expel the powder

The nitrogen or CO₂ is only the propellant that expels and carries the powder; the dry chemical powder itself is the extinguishing agent, breaking the fire's chain reaction. The powder gives no cooling, so hot steel can re-ignite the gas.

6. Cargo information data sheets (SDS) should be posted…

A. in the cargo control room and where the crew can consult them
B. in the master's cabin only
C. with the agent ashore
D. in the engine control room only

Answer: A — in the cargo control room and where the crew can consult them

SDS must be available to the people who need them — in the cargo control room and where the crew can consult them. An SDS locked away is of no use to a casualty or to those planning the cargo operation.

7. Vinyl chloride monomer (VCM) is a colourless liquid with…

A. no odour, and is chemically inert
B. a pungent odour and is non-toxic
C. a sweet odour; it is a known human carcinogen and polymerises
D. an odour of rotten eggs and is an asphyxiant only

Answer: C — a sweet odour; it is a known human carcinogen and polymerises

VCM has a faint sweet odour, is a known human carcinogen and readily polymerises, so it is carried with an inhibitor and exposure is strictly controlled. The pleasant smell is exactly the danger — it gives no useful warning of exposure.

8. Which of these is NOT an inefficient/slow method of discharging a gas carrier?

A. Discharge by cargo PUMPS
B. Discharge by pressurising the tank with vapour
C. Discharge using shore vapour
D. Discharge by boil-off only

Answer: A — Discharge by cargo PUMPS

Pumped discharge is the fast, normal method. Pushing liquid out by pressurising the tank with vapour (or shore vapour, or boil-off) is slow and inefficient, used only on small pressurised ships or when the pumps are unavailable.

9. On all cargo liquid lines where liquid can be shut in between two valves, what must be fitted?

A. A sample point
B. A blank flange
C. A drain cock
D. A relief (safety) valve

Answer: D — A relief (safety) valve

A relief (safety) valve. Cryogenic liquid trapped between two closed valves warms, expands and will burst the line (hydraulic lock). Every section that can be isolated with liquid in it must be relieved back to a tank or the vapour line.

10. Dry chemical powder is discharged from an extinguisher or fixed installation as a…

A. liquid jet
B. dense cloud of fine particles
C. foam blanket
D. fine water mist

Answer: B — dense cloud of fine particles

It leaves as a dense cloud of fine particles carried by the nitrogen/CO₂ propellant, directed at the base of the flame to interrupt the combustion chain reaction. It does not cool and leaves no lasting blanket, so re-ignition off hot steel is the danger.

11. The responsibilities of officers and crew in an emergency are defined in…

A. the charter party
B. the cargo manifest
C. the Safety Management System (ISM) — with emergency duties on the Muster List
D. the classification society rules

Answer: C — the Safety Management System (ISM) — with emergency duties on the Muster List

Under the ISM Code, the company's Safety Management System defines shipboard duties and authority, and each person's emergency duties appear on the Muster List. Know your station before the alarm sounds, not after.

12. The approximate weight of 1 SCM (standard cubic metre) of natural gas is…

A. 0.075 kg
B. 0.75 kg
C. 7.5 kg
D. 75 kg

Answer: B — 0.75 kg

About 0.75 kg — methane is roughly 0.68 kg/m³ at standard conditions and natural gas 0.7–0.8 depending on composition. This is an order-of-magnitude check: natural gas is far lighter than air (~1.2 kg/m³).

13. The heat used to raise the temperature of a substance WITHOUT changing its state is called…

A. latent heat
B. specific heat of vaporisation
C. heat of combustion
D. sensible heat

Answer: D — sensible heat

Sensible heat — the heat you can sense on a thermometer, changing temperature without changing state. Latent heat, by contrast, changes state at constant temperature; that is what a boiling-off cargo consumes.

14. Type 1G ships must be used for cargoes representing the greatest hazard, such as…

A. propane
B. butane
C. chlorine
D. methane (LNG)

Answer: C — chlorine

Chlorine. Type 1G gives the maximum preventive measures and greatest survivability for the most hazardous cargoes. The IGC Code types a ship by the hazard of the cargo it may carry; LNG, for example, is carried on 2G ships.

15. On gas carriers, bunkering by barge during cargo operations…

A. is only permitted under a specific written risk assessment agreed by ship and terminal
B. is always permitted
C. is decided by the bunker barge master
D. requires no separate deck watch

Answer: A — is only permitted under a specific written risk assessment agreed by ship and terminal

There is no blanket ban on simultaneous operations (SIMOPS), but bunkering during cargo work is allowed only under a specific written risk assessment agreed by ship and terminal, with separate teams and watches — because it multiplies the sources of spill and ignition.

16. The toxicity of a substance in air is influenced by…

A. concentration only
B. duration of exposure only
C. the ambient temperature only
D. concentration AND duration of exposure

Answer: D — concentration AND duration of exposure

Both concentration and duration — which is why exposure limits come in pairs: the TWA (8-hour average) and the STEL (15-minute). A high concentration for a short time and a low one for a long time can each cause harm.

17. Why must cargo tanks be cooled down before bulk loading a refrigerated cargo?

A. to increase the tank's volume
B. to avoid flash evaporation and severe thermal stress on the tank structure
C. to remove the inert gas
D. to raise the tank pressure

Answer: B — to avoid flash evaporation and severe thermal stress on the tank structure

Loading very cold liquid into a warm tank would flash off huge volumes of vapour (over-pressure and heavy venting) and thermally shock the steel toward brittle fracture. Cool-down is done gradually with spray until the required temperature is reached.

18. ______ occurs when the blood cannot take a sufficient supply of oxygen to the brain.

A. Narcosis
B. Asphyxia
C. Frostbite
D. Chemical burn

Answer: B — Asphyxia

Asphyxia. Its great danger is that it gives no warning — the victim simply loses consciousness. This is why an enclosed space is never entered without a gas test and a permit.

19. Hydrate formation during cargo loading can be avoided by…

A. adding water to the cargo
B. raising the cargo temperature
C. drying the system, and using an approved antifreeze only with the shipper's written permission
D. increasing the loading rate

Answer: C — drying the system, and using an approved antifreeze only with the shipper's written permission

Hydrates are ice-like solids that block lines and jam valves; they form when water is present. Prevent them by drying the system, and use antifreeze (e.g. methanol) only with the shipper's written agreement, since it contaminates the cargo.

20. Fire hydrants must be positioned such that…

A. one jet can reach any part of the vessel
B. all hydrants are on the same side
C. they are only on the main deck
D. TWO jets, not from the same hydrant, can reach any part of the vessel

Answer: D — TWO jets, not from the same hydrant, can reach any part of the vessel

Two jets, not both from the same hydrant, must be able to reach any part of the vessel — so a single damaged hydrant cannot leave an area unprotected.

21. An uncontrolled release of liquid or vapour can occur through…

A. overfilling a tank
B. hose or manifold failure
C. valve or flange leakage, or tank over-pressure
D. ALL of the above

Answer: D — ALL of the above

All of these. This is precisely why the ESD system exists, and why the deck watch and the ship/shore safety checklist matter throughout the transfer.

22. At atmospheric pressure, ammonia boils at…

A. −33 °C
B. −42 °C
C. −104 °C
D. −162 °C

Answer: A — −33 °C

About −33 °C. (−42 °C is propane, −104 °C ethylene, −162 °C LNG/methane.) Its critical temperature is +132 °C, so ammonia can also be carried fully pressurised at ambient temperature.

23. The main hazards of a vapour cloud are…

A. it drifts to a source of ignition (fire / explosion)
B. it may be toxic
C. it displaces oxygen (asphyxiation)
D. ALL of the above

Answer: D — ALL of the above

All three. And the flammable cloud extends beyond the visible white fog — that fog is condensed water vapour from the air, so the real hazard reaches further than the eye suggests.

24. How is the suction capacity — and so the discharge rate — regulated?

A. by the vapour return line only
B. by the discharge valve and the pump speed
C. by the shore tank level
D. by the cargo temperature

Answer: B — by the discharge valve and the pump speed

By throttling the DISCHARGE valve and, where fitted, varying pump speed. You never throttle the suction — starving a cryogenic pump causes cavitation and destroys it.

25. Venting capacity is based on the maximum volume of cargo entering the tank PLUS…

A. the vapour generated during loading (flash and boil-off)
B. the volume of inert gas
C. the volume of the cargo pumps
D. the ballast displaced

Answer: A — the vapour generated during loading (flash and boil-off)

Plus the vapour generated in the tank as loading proceeds. The relief system must be able to vent the incoming liquid volume AND the vapour it flashes off, or the tank will over-pressurise.

26. What arrangement is fitted in vent masts to snuff out flames?

A. a bursting disc
B. a pressure gauge
C. a drain valve
D. a nitrogen purge / fire-smothering connection and a flame screen

Answer: D — a nitrogen purge / fire-smothering connection and a flame screen

A nitrogen (fire-smothering) connection plus a flame screen/arrester. If a vent ignites you smother the flame at the mast head with nitrogen — you do not try to blow it out — while the flame screen stops flame passing back into the tank.

27. Entering an enclosed space can prove fatal when the oxygen level is…

A. below 19.5 per cent
B. above 23.5 per cent
C. between 20.8 and 21.0 per cent
D. BOTH a and b

Answer: D — BOTH a and b

Both extremes are dangerous. Below 19.5% is oxygen-deficient (asphyxiation), while above 23.5% is oxygen-enriched, where even hard-to-burn materials flash. Normal air is about 20.9%, which is the safe condition, not a hazard.

28. Which method is most widely used for TRACE gas analysis?

A. Catalytic (explosimeter) sensor
B. Infrared tankscope
C. Chemical indicator (detector) tubes
D. Paramagnetic oxygen cell

Answer: C — Chemical indicator (detector) tubes

Chemical indicator (detector) tubes — e.g. Dräger — measure toxic gases at ppm level. An explosimeter reads %LEL and a tankscope reads %volume; neither can resolve the trace concentrations that detector tubes are made for.

29. Which statement about combustible gas indicators (explosimeters) is TRUE?

A. They are calibrated to read the percentage chance of explosion
B. They do NOT work properly where there is a lack of oxygen
C. They will detect a lack of oxygen
D. One sample of air is adequate to test a whole tank

Answer: B — They do NOT work properly where there is a lack of oxygen

They need oxygen to burn the sample on the catalytic filament, so in an inerted tank an explosimeter reads a false low — dangerously reassuring. They are calibrated in %LEL (not 'chance of explosion'), do not detect oxygen deficiency, and several representative samples are needed to test a tank. Use a tankscope (%volume) in an inert atmosphere.

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LGTCO/LGTF exit exam questions and answers — Set 20 — Liquefied Gas Tanker Cargo Operations

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