A white powdery substance produced by the reaction of ammonia with carbon dioxide

The chemical union of two or more molecules of the same compound to form a larger molecule of a new compound

A white powdery substance produced by the reaction of ammonia with carbon dioxide

The chemical union of two or more molecules of the same compound to form a larger molecule of a new compound

LGTCO/LGTF exit exam questions and answers — Set 9 — Liquefied Gas Tanker Cargo Operations

Set 9 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 9 — 30 LGTCO/LGTF exit exam questions with answers

1. In a ship's ESD system, the automatic devices fitted at each tank dome and at both manifold platforms that activate the ESD due to a rise in temperature are known as:

A. Automatic fusible elements
B. Automatic push buttons
C. Infrared gas detection system
D. Automatic smoke sensors

Answer: A — Automatic fusible elements

Fusible elements fitted at tank domes and cargo manifolds melt in a fire and activate the emergency shutdown, closing ESD valves and stopping cargo pumps and compressors, as required by the IGC Code.

2. The bottle under the cap of a soda-acid water extinguisher contains:

A. Dilute hydrochloric acid (HCl)
B. Concentrated sulphuric acid (H2SO4)
C. Dilute sulphuric acid (H2SO4)
D. Concentrated hydrochloric acid (HCl)

Answer: B — Concentrated sulphuric acid (H2SO4)

A soda-acid extinguisher holds sodium bicarbonate solution with a small glass bottle of concentrated sulphuric acid. Breaking the bottle mixes the acid with the bicarbonate, generating carbon dioxide that expels the water.

3. Which liquefied gas is normally carried fully refrigerated at its atmospheric boiling point of -104°C?

A. Ethylene
B. Propane
C. Butane
D. Ammonia

Answer: A — Ethylene

Ethylene boils at about -104°C at atmospheric pressure and is carried fully refrigerated on ethylene carriers. Propane boils near -42°C, ammonia near -33°C and butane near -0.5°C.

4. The molar mass of hydrogen gas (H2) is approximately:

A. 2 g
B. 12 g
C. 32 g
D. 16 g

Answer: A — 2 g

A hydrogen molecule contains two atoms each of atomic mass about 1, so one mole of H2 has a mass of about 2 g. Carbon is 12, methane 16 and oxygen gas 32 g per mole.

5. The unit of measurement of the amount of a gas (amount of substance) is the:

A. Millibar
B. Mole
C. Gram
D. Pascal

Answer: B — Mole

The SI unit for amount of substance is the mole, containing 6.022 x 10^23 particles. One mole of any ideal gas occupies about 22.4 litres at standard conditions. Millibar and pascal are pressure units.

6. In a vapour pressure experiment where test liquid is introduced above the mercury in a barometer tube, if the tube is heated the mercury level will:

A. Increase
B. Decrease
C. Remain the same
D. Oscillate rapidly

Answer: B — Decrease

Heating the test liquid increases its saturated vapour pressure in the space above the mercury. The higher vapour pressure pushes the mercury column down, so its level decreases, demonstrating that vapour pressure rises with temperature.

7. Which statement is correct regarding typical HSE performance indicators?

A. Lost Time Injury Frequency (LTIF) is the number of lost-time injuries per 1 million man-hours worked
B. Total Recordable Case Frequency (TRCF) is the number of recordable cases per 1 million man-hours worked
C. LTIF is the number of fatalities per 1,000 man-hours worked
D. Both the LTIF and TRCF definitions given are correct

Answer: D — Both the LTIF and TRCF definitions given are correct

Shipping and oil industry KPIs normalise injury rates per one million man-hours worked. LTIF counts injuries causing lost time, while TRCF counts all recordable cases including fatalities, lost time, restricted work and medical treatment cases.

8. At the commencement of loading on a gas carrier, cargo should be loaded:

A. At a slow initial rate until all systems are checked
B. Directly at full high-pressure rate
C. With the vent mast valves open
D. With the ESD system bypassed

Answer: A — At a slow initial rate until all systems are checked

Loading starts at a slow rate to confirm cargo is going into the correct tanks, check for leaks, allow gradual cooling of pipes and tanks, and avoid pressure surges and excessive vapour generation. The rate is increased only after checks are satisfactory.

9. To be liquefied by pressure alone, a gas must first be cooled to a temperature:

A. Below its critical temperature
B. Above its critical temperature
C. Equal to its flash point
D. Above its auto-ignition temperature

Answer: A — Below its critical temperature

Above its critical temperature a gas cannot be liquefied however much pressure is applied. It must be below the critical temperature, which is why methane, with a critical temperature of about -82.5°C, is carried fully refrigerated.

10. Which class of fire does a flammable gas fire fall under?

A. Class A fire
B. Class B fire
C. Class C fire
D. Class F fire

Answer: C — Class C fire

Under the European classification used on Indian-flag and most ships, Class C covers fires involving flammable gases such as LPG and LNG. Class A is solids, Class B liquids and Class F cooking oils.

11. Which of these liquefied gases is NOT flammable?

A. Chlorine
B. Ethylene
C. Ethylene oxide
D. Propylene oxide

Answer: A — Chlorine

Chlorine is a toxic, oxidising gas that does not burn, though it supports combustion of some materials. Ethylene, ethylene oxide and propylene oxide are all flammable cargoes.

12. Semi-pressurised ships capable of carriage temperatures down to -104°C cannot carry which of the following?

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

Answer: A — Methane

Methane boils at about -162°C at atmospheric pressure and its critical temperature is about -82.5°C, so it cannot be carried at -104°C under moderate pressure. Ethylene, ethane, propane and butane can be carried on such ships.

13. What is the purpose of inerting?

A. Primarily to prevent flammable vapour/air mixtures in tanks and piping
B. Primarily to increase the oxygen content in tanks and piping
C. Primarily to increase the hydrocarbon content in tanks and piping
D. Primarily to increase both oxygen and hydrocarbon content in tanks and piping

Answer: A — Primarily to prevent flammable vapour/air mixtures in tanks and piping

Inerting replaces air in tanks and pipelines with inert gas or nitrogen, reducing the oxygen content below the level needed for combustion. This prevents flammable vapour/air mixtures from forming during operations such as gassing-up or gas-freeing.

14. What is the name of the certificate issued by the flag Administration confirming that the structure, equipment, fittings, arrangements and materials of a gas carrier comply with the relevant Gas Code?

A. Certificate of Construction
B. Load Line Certificate
C. Safety Construction Certificate
D. Certificate of Fitness

Answer: D — Certificate of Fitness

After the IGC Code survey, the Administration issues the International Certificate of Fitness for the Carriage of Liquefied Gases in Bulk, confirming construction and equipment comply with the Code and listing the permitted cargoes.

15. For fixed gas detection systems, the Gas Codes require the sampling interval from any one space generally not to exceed:

A. 60 minutes
B. 30 minutes
C. 45 minutes
D. 20 minutes

Answer: B — 30 minutes

The IGC Code permits sequential sampling systems provided the time between samples from any one location does not exceed 30 minutes, so that a developing leak is detected promptly.

16. What chemical is used in a BC-type dry chemical powder extinguisher?

A. Aluminium sulphate
B. Sodium bicarbonate
C. Mono-ammonium phosphate
D. Sodium, magnesium and aluminium

Answer: B — Sodium bicarbonate

BC powders are based mainly on sodium bicarbonate, effective on flammable liquid and gas fires. Mono-ammonium phosphate is used in ABC multipurpose powders, and special powders are used for metal fires.

17. For cargo tank entry, the toxic gas concentration should be:

A. Less than the OEL
B. Less than 80% of the OEL
C. Less than 50% of the OEL
D. Less than 60% of the OEL

Answer: C — Less than 50% of the OEL

ISGOTT and gas tanker entry guidance require toxic vapour concentrations below 50% of the occupational exposure limit before entry without breathing apparatus, along with 21% oxygen and hydrocarbons not more than 1% LFL.

18. The fixed gas detection system alarm is activated when the vapour concentration reaches:

A. 10% of the lower flammable limit (LFL)
B. 30% of the lower flammable limit (LFL)
C. 20% of the lower flammable limit (LFL)
D. 40% of the lower flammable limit (LFL)

Answer: B — 30% of the lower flammable limit (LFL)

The IGC Code requires the fixed gas detection system to give audible and visual alarms when the flammable vapour concentration reaches 30% of the lower flammable limit, allowing action before a flammable atmosphere develops.

19. Dräger tubes and pump are used to measure which type of gas?

A. Toxic gas
B. Flammable gas
C. Oxygen
D. Inert gas

Answer: A — Toxic gas

Chemical stain detector tubes such as Dräger tubes measure low concentrations of specific toxic gases, for example ammonia, H2S, benzene or CO, by a colour change. Flammable gas and oxygen are measured with explosimeters and oxygen analysers.

20. What is the typical thickness of the primary membrane of membrane cargo tanks?

A. 2.0 to 3.7 mm
B. 0.7 to 1.5 mm
C. 4.0 to 5.0 mm
D. 8.5 to 10.0 mm

Answer: B — 0.7 to 1.5 mm

Membrane barriers are very thin: GTT NO96 uses about 0.7 mm Invar and Mark III uses about 1.2 mm corrugated stainless steel. The thin membrane relies on the insulation and hull for support.

21. Float gauges on liquefied gas tankers are an example of which type of gauging system?

A. Closed devices which do not penetrate the cargo tank
B. Restricted gauging
C. Closed devices which penetrate the cargo tank
D. Indirect systems

Answer: C — Closed devices which penetrate the cargo tank

The IGC Code classes float gauges as closed gauging devices that penetrate the tank but form part of a closed system, so cargo is not released. Restricted devices, such as sounding pipes, release a small amount of vapour or liquid when used.

22. The contents of a liquefied gas cargo tank are bounded by the:

A. Secondary barrier
B. Primary barrier
C. Interbarrier space
D. Ship's inner hull

Answer: B — Primary barrier

Under the IGC Code the primary barrier is the inner element designed to contain the cargo. The secondary barrier is a liquid-resisting outer element provided to contain any leakage through the primary barrier temporarily; the interbarrier space lies between them.

23. What are peroxides?

A. A white powdery substance produced by the reaction of ammonia with carbon dioxide
B. Compounds formed by the interaction of water and hydrocarbons at certain pressures and temperatures
C. Compounds formed by the chemical combination of cargo liquid or vapour with atmospheric oxygen or oxygen from another source
D. The chemical union of two or more molecules of the same compound to form a larger molecule of a new compound

Answer: C — Compounds formed by the chemical combination of cargo liquid or vapour with atmospheric oxygen or oxygen from another source

Peroxides form when cargoes such as butadiene or vinyl chloride react with oxygen. They are unstable and can trigger uncontrolled polymerisation or explosion, which is why oxygen content is kept very low and inhibitors are used for such cargoes.

24. What are hydrates?

A. A white powdery substance produced by the reaction of ammonia with carbon dioxide
B. Compounds formed by the interaction of water and hydrocarbons at certain pressures and temperatures
C. Compounds formed by the chemical combination of cargo liquid or vapour with atmospheric oxygen
D. The chemical union of two or more molecules of the same compound to form a larger molecule of a new compound

Answer: B — Compounds formed by the interaction of water and hydrocarbons at certain pressures and temperatures

Hydrates are ice-like crystals formed when free water combines with hydrocarbons such as propane or butane under certain pressure and temperature conditions. They can block valves, pumps and gauge lines, so cargo systems are dried and freezing-point depressants such as methanol may be used.

25. What is the atmospheric boiling point of ammonia?

A. -33.4 °C
B. -45.4 °C
C. -42.4 °C
D. -29.6 °C

Answer: A — -33.4 °C

Anhydrous ammonia boils at about -33.4 °C at atmospheric pressure. It is therefore carried fully refrigerated at about -33 °C or pressurised at ambient temperature, and it is also toxic, so it requires toxic-cargo precautions under the IGC Code.

26. What is the mode of operation of the fixed dry chemical powder monitors on deck?

A. Only locally from deck
B. Both locally and remotely
C. Only remotely from the bridge or cargo control room
D. Only remotely from the bridge

Answer: B — Both locally and remotely

The IGC Code (Chapter 11) requires the dry chemical powder system to be capable of activation from more than one position. Deck monitors can be started remotely, for example from a fire station or control position, and can also be operated and aimed locally at the monitor.

27. A liquefied gas is a liquid which has a saturated vapour pressure exceeding:

A. 2.8 bar absolute at 37.8 °C
B. 3.8 bar absolute at 37.8 °C
C. 2.8 bar absolute at 27.8 °C
D. 3.8 bar absolute at 27.8 °C

Answer: A — 2.8 bar absolute at 37.8 °C

The IGC Code defines liquefied gases as liquids with a vapour pressure exceeding 0.28 MPa (2.8 bar) absolute at 37.8 °C. Products below this limit are generally carried as bulk liquid chemicals under the IBC Code.

28. How many pressure relief valves must be fitted to a cargo tank of more than 20 m³ capacity?

A. At least one
B. At least two
C. At least three
D. At least four

Answer: B — At least two

IGC Code Chapter 8 requires each cargo tank with a volume of more than 20 m³ to have at least two pressure relief valves of about equal capacity. Tanks of 20 m³ or less may have a single relief valve.

29. What should you do when the general emergency alarm sounds?

A. Wear PPE and lifejacket, carry the immersion suit and go to the bridge
B. Wear PPE and lifejacket, carry the immersion suit and go to the engine room
C. Wear PPE and lifejacket, carry the immersion suit and go to the forecastle
D. Wear PPE and lifejacket, carry the immersion suit and go to the designated muster point as shown in the ship's muster list

Answer: D — Wear PPE and lifejacket, carry the immersion suit and go to the designated muster point as shown in the ship's muster list

On the general emergency alarm every crew member must proceed, suitably dressed with lifejacket and immersion suit, to the muster station allocated in the muster list required by SOLAS III/8 and III/37. Duties are then assigned from the muster station.

30. Under the European/ISO classification used in Indian training, an LNG fire is classified as which class of fire?

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

Answer: C — Class C

In the European/ISO system Class C covers fires involving flammable gases such as methane, propane and butane. Class A is solid combustibles, Class B flammable liquids and Class D burning metals. The primary action for a gas fire is to isolate the gas source.

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