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LGTCO/LGTF exit exam questions and answers — Set 8 — Liquefied Gas Tanker Cargo Operations

Set 8 of the Liquefied Gas Tanker Cargo Operations (LGTCO/LGTF) exit exam bank — 30 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 8 — 30 LGTCO/LGTF exit exam questions with answers

1. Which of the following is the ultimate source of energy on Earth?

  • A. LNG
  • B. Nuclear
  • C. Solar
  • D. CNG
Answer: C — Solar
Almost all of Earth's energy resources, including fossil fuels such as natural gas, derive ultimately from solar energy captured by ancient plants and organisms through photosynthesis, so the sun is regarded as the ultimate source.

2. Which characteristics should insulation materials possess for use on gas carriers?

  • A. Low thermal conductivity and ability to bear loads
  • B. Ability to withstand mechanical damage, and light weight
  • C. Being unaffected by cargo liquid or vapour
  • D. All of the above
Answer: D — All of the above
Gas carrier insulation must limit heat ingress through low thermal conductivity, carry loads from the tank, resist mechanical damage and vibration, be light, and remain chemically unaffected by cargo, as required by the IGC Code.

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

  • A. Inert gas high temperature alarm
  • B. Inert gas low flow alarm
  • C. Inert gas low pressure alarm
  • D. Inert gas reverse flow alarm
Answer: C — Inert gas low pressure alarm
The FSS Code requires a low pressure alarm on the inert gas main downstream of the non-return devices to warn when supply pressure falls, which could allow tank pressure to drop and air to enter the tanks.

4. How is cooling and cleaning water supplied to the inert gas scrubber tower?

  • A. By the main sea water pump
  • 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
A dedicated scrubber sea water pump supplies water to cool the flue gas and wash out soot and sulphur oxides. The FSS Code requires a reliable water supply, with an alternative pump available, so that the inert gas plant can operate.

5. The space enclosed by the ship's structure in which a cargo containment system is situated is called the:

  • A. Hold space
  • B. Compressor room
  • C. Motor room
  • D. Engine room
Answer: A — Hold space
The IGC Code defines a hold space as the space enclosed by the ship's structure in which a cargo containment system is situated. Hold spaces are inerted or filled with dry air depending on the tank type and cargo.

6. Self-contained breathing apparatus (SCBA) is also called:

  • A. ELSA
  • B. EEBD
  • C. Compressed air breathing apparatus (CABA)
  • D. None of the above
Answer: C — Compressed air breathing apparatus (CABA)
SCBA is also known as compressed air breathing apparatus because the wearer breathes air from a high-pressure cylinder carried on the back. ELSA and EEBD are short-duration escape sets, not for firefighting or rescue.

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

  • A. Vent the casing
  • B. Tighten the packing
  • C. Close the discharge
  • D. Re-prime the pump
Answer: A — Vent the casing
With a positive suction head, liquid will refill the pump once trapped air is released, so venting the casing is the first action. Priming is unnecessary because the suction is flooded.

8. On gas carriers, any pipework entering or leaving a cargo tank must do so through the ____ of the tank.

  • A. Aft end
  • B. Top
  • C. Bottom
  • D. Forward end
Answer: B — Top
The IGC Code requires cargo piping connections to tanks to be above the highest liquid level, normally through the tank dome on top, so that a pipe failure cannot drain liquid cargo from the tank.

9. Which of the following is NOT an alarm on an inert gas plant?

  • A. Low pressure alarm
  • B. Low oxygen alarm
  • C. Deck seal low water level alarm
  • D. Scrubber high water level alarm
Answer: B — Low oxygen alarm
The FSS Code requires a high oxygen content alarm, not a low oxygen alarm, because the danger is inert gas with too much oxygen. Low pressure, low deck seal water and high scrubber water level alarms are all required.

10. The purpose of remote tank level measurement is to measure the:

  • A. Height from the liquid surface to the top stringers in the tank
  • B. Height of liquid in the tank
  • C. Height from the bottom shell to the top stringers in the tank
  • D. Height of the bottom girders in the tank
Answer: B — Height of liquid in the tank
Remote level gauges measure liquid level in the tank, from which volume is derived using calibration tables. This allows cargo quantity monitoring and overfill prevention without opening the tank.

11. What are the symptoms of asphyxia when LPG and LNG are carried as cargo?

  • A. Increased rate and depth of respiration and loss of consciousness
  • B. Blueness of the skin
  • C. Stertorous breathing with a snoring sound
  • D. All of the above
Answer: D — All of the above
LPG and LNG vapours displace oxygen. Oxygen deficiency causes rapid deep breathing, cyanosis (blue skin), stertorous snoring respiration and eventually loss of consciousness and death. Rescuers must wear breathing apparatus.

12. How is sea water supplied to the inert gas deck seal?

  • A. Through the main sea water pumps or the cargo condenser pump
  • B. Through a sea water pump fitted on the cargo deck
  • C. Through the deck fire line
  • D. Through the deck seal pump fitted in the engine room
Answer: D — Through the deck seal pump fitted in the engine room
A dedicated deck seal pump, normally in the engine room or another gas-safe space, maintains the water seal at all times. The FSS Code requires the seal water supply to be maintained even when the IG plant is shut down.

13. What is the boiling point of ammonia at atmospheric pressure?

  • A. -42°C
  • B. -33°C
  • C. -5°C
  • D. None of the above
Answer: B — -33°C
Ammonia boils at about -33°C at atmospheric pressure. Propane boils at about -42°C and butane near -0.5°C, so ammonia is carried fully refrigerated around -33°C or under pressure at ambient temperature.

14. Ammonia can form explosive compounds with:

  • A. Mercury alone
  • B. Mercury, chlorine, iodine, bromine, calcium, silver oxide and silver hypochlorite
  • C. Silica
  • D. Water
Answer: B — Mercury, chlorine, iodine, bromine, calcium, silver oxide and silver hypochlorite
Ammonia reacts with mercury, halogens such as chlorine, iodine and bromine, calcium, silver oxide and silver hypochlorite to form explosive compounds. For this reason mercury instruments and incompatible materials are prohibited in ammonia service.

15. Under the IGC Code, cargo tanks of any gas carrier type must be located at a minimum distance from the side shell plating of:

  • A. 760 mm
  • B. 750 mm
  • C. 740 mm
  • D. 730 mm
Answer: A — 760 mm
IGC Code Chapter 2 requires cargo tanks on all ship types to be located at least 760 mm inboard from the shell plating, with greater distances for Type 1G ships, to protect them from collision or grounding damage.

16. When seller and buyer agree to Free On Board (FOB) terms, what does the buyer pay?

  • A. Freight, insurance, unloading costs and onward transport
  • B. Only insurance, unloading costs and onward transport
  • C. Nothing, as the buyer owns the ship
  • D. Only unloading and onward transport
Answer: A — Freight, insurance, unloading costs and onward transport
Under FOB, the seller delivers the cargo on board at the loading port, after which risk and cost pass to the buyer. The buyer therefore pays freight, insurance, discharge costs and onward transportation.

17. In a Moss-type LNG cargo tank, where are the pumps, pipework and cabling secured?

  • A. In a tubular tower inside the cargo tank
  • B. In the liquid dome area on the main deck
  • C. In the vapour dome area on the main deck
  • D. In the pump room close to the manifold
Answer: A — In a tubular tower inside the cargo tank
Moss spherical tanks have a central vertical tubular tower running from the dome to the bottom, supporting the submerged cargo pumps, loading and discharge pipes, instrumentation and cabling.

18. Which code would you refer to for the requirements for an LNG cargo containment system?

  • A. SIGTTO guidelines
  • B. IBC Code
  • C. IGC Code
  • D. OCIMF guidelines
Answer: C — IGC Code
Containment system design, materials, insulation and testing requirements for liquefied gas carriers are set out in Chapter 4 of the IGC Code. SIGTTO and OCIMF issue industry guidance, and the IBC Code covers chemicals.

19. Under the IGC Code, what is the minimum distance of cargo tanks from the bottom shell plating for any gas tanker type?

  • A. B/10 or 1.5 m, whichever is less
  • B. B/5 or 3.0 m, whichever is less
  • C. B/15 or 2 m, whichever is less
  • D. B/4 or 2.4 m, whichever is less
Answer: C — B/15 or 2 m, whichever is less
IGC Code Chapter 2 requires cargo tanks to be located above the bottom shell at a distance of not less than B/15 or 2 m, whichever is less, measured at the centreline, to protect them from grounding damage.

20. On an LNG tanker, what is the option available to control cargo tank pressure when gas burning is not possible?

  • A. Stop the voyage until pressure stabilises
  • B. Jettison cargo until not less than 80% by volume remains
  • C. Heat the boil-off gas and vent it to atmosphere via the vent mast riser
  • D. Open all cargo tank safety valves
Answer: C — Heat the boil-off gas and vent it to atmosphere via the vent mast riser
If boil-off cannot be burned or reliquefied, it may as a last resort be heated and vented through the vent mast. Heating makes the methane lighter than air so it disperses upwards rather than falling onto the deck.

21. Which machinery is used for the initial pressurisation of insulation spaces?

  • A. Boiler
  • B. Evaporator
  • C. Nitrogen generator
  • D. Vacuum pump
Answer: C — Nitrogen generator
Membrane LNG insulation spaces are filled and kept slightly above atmospheric pressure with dry nitrogen from the nitrogen generator. This prevents air and moisture ingress and allows leak detection by gas analysis.

22. On an LNG carrier during loading, what happens when a tank's cargo level reaches 99% of its volume capacity?

  • A. The alarm sounds but topping-up continues
  • B. The emergency mooring release is activated
  • C. The vent risers open automatically
  • D. The very high level alarm is initiated and the ESD is activated
Answer: D — The very high level alarm is initiated and the ESD is activated
The IGC Code requires an independent high-level overflow control that automatically closes tank filling valves or activates ESD to prevent overfilling. On LNG carriers this very high level trip is typically set at 99% volume.

23. What will happen if cold LNG boil-off gas is vented through the mast riser?

  • A. The mast riser will freeze and may crack
  • B. The methane vapour will catch fire immediately
  • C. The methane vapour will turn back into liquid LNG
  • D. A large white plume will be produced
Answer: D — A large white plume will be produced
Cold methane vented to atmosphere chills the surrounding air below its dew point, condensing moisture into a dense white plume. Cold methane is also heavier than air below about -110°C, so it is heated before venting.

24. Under the IGC Code, what is the general maximum allowable filling limit for cargo tanks?

  • A. 98.5%
  • B. 98.6%
  • C. 98%
  • D. 99.0%
Answer: C — 98%
IGC Code Chapter 15 sets the basic filling limit at 98% of tank volume at the reference temperature, ensuring vapour space remains so that liquid does not reach the relief valves as the cargo warms and expands.

25. Pressurising insulation spaces with nitrogen slightly above atmospheric pressure prevents:

  • A. Formation of explosive mixtures and ingress of moisture and air
  • B. A fall in cargo tank temperature
  • C. Collapse of the inflated insulation boxes
  • D. Accidental vacuum leading to membrane collapse
Answer: A — Formation of explosive mixtures and ingress of moisture and air
Dry nitrogen at a slight positive pressure keeps air and moisture out of the insulation spaces, preventing flammable mixtures if cargo leaks, avoiding ice formation and loss of insulation efficiency, and allowing leak detection.

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

  • A. Burst of the discharge line
  • B. Formation of cold spots in a ballast tank
  • C. Possible damage to the cargo pump during discharge
  • D. Icing-up of the discharge pump casing externally
Answer: C — Possible damage to the cargo pump during discharge
Moisture left in tanks freezes at cargo temperature and forms ice or hydrates. Ice particles can be drawn into submerged cargo pumps, damaging impellers and bearings, and can block pipes, valves and gauges.

27. When heat is transferred from one body to another, what is transferred?

  • A. Molecules
  • B. Power
  • C. Electrons
  • D. Energy
Answer: D — Energy
Heat is a form of energy, and heat transfer is the flow of thermal energy from a hotter body to a cooler one by conduction, convection or radiation. Neither mass nor electrons need be transferred.

28. Up to what temperature is methane vapour heavier than air?

  • A. -161.5°C
  • B. 15°C
  • C. -121.5°C
  • D. -110.5°C
Answer: D — -110.5°C
Methane vapour is lighter than air at ambient temperature, but when colder than about -110°C its density exceeds that of air. Cold vapour from an LNG spill therefore stays low until it warms up.

29. How many portable gas detectors should be carried on board an LNG carrier?

  • A. At least one with methane and one with propane detection capability
  • B. At least one with methane and one with carbon monoxide detection capability
  • C. At least one with methane and one with ammonia detection capability
  • D. At least two sets with methane detection capability
Answer: D — At least two sets with methane detection capability
The IGC Code requires at least two sets of portable gas detection equipment acceptable for the products carried. On an LNG carrier, these must be capable of measuring methane, with oxygen analysers also provided.

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

  • A. Continuous catalytic combustion system
  • B. Infrared type with sequential sampling
  • C. Portable gas detection system
  • D. Spot metering detectors fixed inside each insulation space
Answer: B — Infrared type with sequential sampling
Insulation spaces of LNG carriers are monitored by a fixed sampling system that draws samples sequentially to an infrared analyser in a safe space. Infrared works in the nitrogen atmosphere where catalytic sensors would fail without oxygen.

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