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LGTCO/LGTF exit exam questions and answers — Set 16 — Liquefied Gas Tanker Cargo Operations

Set 16 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.

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 16 — 30 LGTCO/LGTF exit exam questions with answers

1. A crew member wants to carry an aluminium step-ladder onto the cargo deck during transfer, arguing that aluminium does not rust. Why is aluminium banned from the hazardous area?

  • A. It is too heavy to handle safely near the manifold
  • B. It corrodes in salt air and contaminates the cargo
  • C. It builds up a static charge faster than steel
  • D. A trace of aluminium smeared on rusty steel can throw an incendive (thermite) spark if that steel is later struck
Answer: D — A trace of aluminium smeared on rusty steel can throw an incendive (thermite) spark if that steel is later struck
Aluminium smeared onto rusted steel can give an incendive (thermite) spark if the steel is struck later — an ignition source that outlasts the ladder itself — which is why aluminium is banned from hazardous areas. The reason is ignition, not weight or corrosion.

2. Charge is generated whenever cargo is loaded, yet a static discharge inside a loaded gas-carrier tank does not start a fire. What is the PRIMARY reason?

  • A. The loading rate is always kept below 1 m/s, as on oil tankers
  • B. The tank is handled closed and kept inerted, so no flammable air/vapour mixture exists for a discharge to ignite
  • C. Bonding the manifold drains all charge out of the liquid surface
  • D. Gas cargoes cannot separate or hold an electrostatic charge
Answer: B — The tank is handled closed and kept inerted, so no flammable air/vapour mixture exists for a discharge to ignite
The gas-carrier primary defence is the closed, inerted tank — with no flammable mixture present, a discharge has nothing to ignite. The 1 m/s slow-load rule is oil-tanker practice; gas cargoes do hold charge, and bonding drains conductors, not the liquid surface.

3. Preparing for an ammonia cargo, an officer notes its TLV-TWA is 25 ppm. What does the TWA figure represent, and how does it compare with the STEL?

  • A. The average exposure permitted over an 8-hour working day; the 15-minute STEL is higher
  • B. The maximum for a single 15-minute exposure; the STEL is lower
  • C. A concentration that must never be exceeded for an instant; the STEL equals it
  • D. The concentration at which the gas becomes flammable; the STEL is unrelated
Answer: A — The average exposure permitted over an 8-hour working day; the 15-minute STEL is higher
The Time-Weighted Average is the average concentration allowed over an 8-hour day, and it is the lowest of the exposure limits; the Short-Term Exposure Limit (up to 15 minutes) is always higher. The ceiling (TLV-C) — the value never to be exceeded — is a separate limit used for fast-acting substances.

4. What arrangement is fitted at a cargo tank vent mast to deal with a vent fire, and how is such a fire tackled?

  • A. A bursting disc, which is removed to fight the fire
  • B. A pressure gauge and a drain valve
  • C. A water sprinkler inside the riser
  • D. A flame screen plus a nitrogen (fire-smothering) connection; a vent fire is smothered with nitrogen, not blown out
Answer: D — A flame screen plus a nitrogen (fire-smothering) connection; a vent fire is smothered with nitrogen, not blown out
Vent masts carry a flame screen/arrester and a nitrogen fire-smothering connection: if a vent ignites you smother it with nitrogen rather than trying to blow it out. A bursting disc or gauge does nothing to extinguish a vent fire.

5. Before enclosed-space entry the oxygen meter must confirm a normal atmosphere. Which set of figures correctly gives normal air, the enrichment limit and the deficiency limit?

  • A. Normal 23.5%; enriched above 25%; deficient below 20.9%
  • B. Normal 19.5%; enriched above 21%; deficient below 16%
  • C. Normal 20.9%; oxygen-enriched above 23.5%; oxygen-deficient below 19.5%
  • D. Normal 21%; enriched above 30%; deficient below 11%
Answer: C — Normal 20.9%; oxygen-enriched above 23.5%; oxygen-deficient below 19.5%
Normal air is 20.9% oxygen; above 23.5% it is oxygen-enriched, with a sharply raised fire risk, and below 19.5% it is oxygen-deficient. The other sets misplace the normal value or the safe limits.

6. A space purged with nitrogen reads 0% hydrocarbon on the gas meter. Two crew enter without breathing apparatus and collapse within a minute. What was the fatal error?

  • A. The hydrocarbon meter was faulty and read a false zero
  • B. A 0% hydrocarbon reading says nothing about oxygen; the nitrogen-purged space held almost no oxygen and gives no warning
  • C. The space was still too cold to enter safely
  • D. Residual toxic vapour lay below the meter's range
Answer: B — A 0% hydrocarbon reading says nothing about oxygen; the nitrogen-purged space held almost no oxygen and gives no warning
A 'no hydrocarbon' reading tells you nothing about oxygen content. A nitrogen-purged space can be near 0% oxygen, and nitrogen has no colour, smell or warning, so entrants drop in seconds. Oxygen (which should read 20.9%) must always be tested separately before entry.

7. A cargo list shows butadiene, vinyl chloride monomer, isoprene and propane. Which one does NOT require a stabilising inhibitor, and why?

  • A. Propane — a saturated hydrocarbon that cannot polymerise
  • B. Vinyl chloride monomer — it is chemically inert
  • C. Butadiene — its two double bonds cancel out
  • D. Isoprene — it is too volatile to react
Answer: A — Propane — a saturated hydrocarbon that cannot polymerise
Inhibitors are needed for polymerisable (unsaturated) cargoes: butadiene, VCM and isoprene all carry reactive carbon–carbon double bonds. Propane is a saturated alkane with single bonds only, so it cannot polymerise and needs no inhibitor.

8. A cargo document lists vinyl chloride monomer. Which description of its properties and hazards is correct?

  • A. Odourless and chemically inert
  • B. A rotten-egg odour, and an asphyxiant only
  • C. A pungent odour but non-toxic
  • D. A sweet odour; a known human carcinogen that polymerises and is shipped inhibited
Answer: D — A sweet odour; a known human carcinogen that polymerises and is shipped inhibited
VCM has a sweet odour, is a known human carcinogen and is polymerisable, so it is carried with an inhibitor. The pleasant smell is exactly why it is dangerous — it does not warn you of a harmful concentration.

9. When preparing a cargo system for ammonia, which materials must be excluded, and why?

  • A. Stainless steel and aluminium, because ammonia dissolves them
  • B. PTFE and other fluoropolymer seals, because ammonia swells them
  • C. Copper, brass and bronze, and zinc/galvanised surfaces, because ammonia attacks them
  • D. Carbon steel, because ammonia cannot be carried in steel tanks
Answer: C — Copper, brass and bronze, and zinc/galvanised surfaces, because ammonia attacks them
Ammonia attacks copper and its alloys (brass, bronze), zinc and galvanised coatings, so such fittings must be excluded and suitable steels used instead. Ammonia is in fact routinely carried in carbon-steel tanks, so banning steel is wrong.

10. A pressurised LPG tank is engulfed in flame; the relief valve is lifting but the shell above the liquid level glows red. What failure is imminent, and what would have prevented it?

  • A. A BLEVE — the shell tears and the contents flash to a fireball; cooling the vapour-space shell with water spray prevents it
  • B. A hydrate blockage; drying the system would prevent it
  • C. A rollover; matching the liquid densities prevents it
  • D. A vacuum collapse; a pressure/vacuum valve prevents it
Answer: A — A BLEVE — the shell tears and the contents flash to a fireball; cooling the vapour-space shell with water spray prevents it
A Boiling Liquid Expanding Vapour Explosion occurs when the steel above the liquid — with no liquid behind it to carry heat away — weakens and tears, flashing the whole contents to a fireball. The relief valve cannot vent fast enough once the shell glows; cooling the vapour-space shell with water spray is what prevents it.

11. An LNG spill on deck produces a drifting white cloud. Which statement about the hazard is correct?

  • A. The flammable cloud ends exactly at the edge of the visible white mist
  • B. The visible mist is condensed water; the flammable, cold vapour reaches beyond it, sinks and drifts downwind
  • C. 1 m³ of LNG makes only a few m³ of vapour, so the cloud is small
  • D. The cloud always rises, because methane is lighter than air
Answer: B — The visible mist is condensed water; the flammable, cold vapour reaches beyond it, sinks and drifts downwind
The white cloud is condensed water vapour from the air; the flammable cloud — cold and initially heavier than air — extends beyond the visible mist, hugs the deck and drifts downwind. 1 m³ of LNG expands to roughly 600–620 m³ of vapour, so a small spill fills a large space, and cold methane sinks until it warms.

12. You need boiling point, vapour density and flammable limits to set a gas detector and predict where a leak will travel. Which SDS section carries these figures?

  • A. Section 2 — Hazards identification
  • B. Section 3 — Composition
  • C. Section 11 — Toxicological information
  • D. Section 9 — Physical and chemical properties
Answer: D — Section 9 — Physical and chemical properties
Section 9 (physical and chemical properties) holds the numbers you dial into equipment — boiling point, flash point, vapour density, LFL/UFL. Section 2 tells you the cargo is flammable but not at what percentage; Section 11 describes health effects, not the physical figures.

13. A crewman is splashed with liquid ammonia. Which SDS section tells you what to DO for him right now, whatever the cargo and wherever the ship?

  • A. Section 8 — Exposure controls / PPE
  • B. Section 2 — Hazards identification
  • C. Section 4 — First-aid measures
  • D. Section 11 — Toxicological information
Answer: C — Section 4 — First-aid measures
Under the GHS every SDS carries the same 16 sections in the same order, and Section 4 is always first-aid measures. Section 8 says what to wear and Section 2 names the hazard, but only Section 4 tells you what to do for the casualty.

14. Loading anhydrous ammonia, you find the folder's 'Ammonia' SDS gives a boiling point of +36 °C and Class 8 Corrosive. What is wrong?

  • A. It is the wrong sheet — those figures are for an ammonia water solution; the anhydrous cargo boils at −33 °C and is Class 2.3 toxic gas
  • B. Nothing — anhydrous ammonia is Class 8 corrosive
  • C. The boiling point is simply a misprint for −36 °C
  • D. Class 8 is right; the boiling point can be ignored
Answer: A — It is the wrong sheet — those figures are for an ammonia water solution; the anhydrous cargo boils at −33 °C and is Class 2.3 toxic gas
Anhydrous ammonia cargo boils at −33 °C and is UN 1005, Class 2.3 toxic gas. A sheet showing +36 °C and Class 8 corrosive is for ammonia solution (ammonium hydroxide) — a different substance whose headline hazard is not the acute toxicity of the cargo. The Section 1 identity must be verified against the cargo.

15. Your catalytic explosimeter reads 100% LEL in a methane/air atmosphere. Given methane's lower explosive limit, how much methane is actually present by volume?

  • A. 100% by volume — the meter reads gas content directly
  • B. 50% by volume
  • C. 15% by volume — the upper limit
  • D. 5% by volume
Answer: D — 5% by volume
The explosimeter scale runs 0–100% of the lower explosive limit, and methane's LEL is about 5% by volume, so a full-scale reading is only 5% gas by volume — the point where the mixture has just become explosive. Reading % LEL as if it were % by volume is the commonest and most dangerous misreading on board.

16. An inerted cargo tank holds 2% oxygen and is full of hydrocarbon vapour. Tested with a catalytic explosimeter, what will it show — and what should be used instead?

  • A. An accurate % LEL, the same as it would read in air
  • B. A false low reading, even zero, because the gas cannot burn on the bead without oxygen; use a tankscope reading % by volume
  • C. A reading over 100% LEL, pegging full scale
  • D. It switches automatically to % by volume
Answer: B — A false low reading, even zero, because the gas cannot burn on the bead without oxygen; use a tankscope reading % by volume
A catalytic (pellistor) explosimeter must burn the sample on its heated bead, which needs oxygen; in an oxygen-deficient inert tank the bead never heats, so the meter quietly reads false low or zero with no warning. A tankscope (non-catalytic hot filament, % by volume) is the correct instrument for an inert atmosphere.

17. You must measure a toxic gas present at only a few parts per million in a tank atmosphere. Which device is the right choice, and why?

  • A. A catalytic explosimeter, because it reads flammable gas
  • B. A tankscope, because it reads % by volume
  • C. A chemical indicator (detector) tube, e.g. Dräger, which measures one named gas down to ppm level
  • D. A paramagnetic oxygen analyser, because it reads up to 25%
Answer: C — A chemical indicator (detector) tube, e.g. Dräger, which measures one named gas down to ppm level
Chemical indicator (detector) tubes are the shipboard device for trace toxic gases — a stain length read in ppm, specific to one named gas. An explosimeter (%LEL) and a tankscope (%volume) cannot resolve ppm concentrations, and an oxygen analyser measures only oxygen.

18. A four-gas personal set reads O₂, %LEL, H₂S and CO. In the enclosed-space entry test sequence, why is oxygen checked first?

  • A. Because oxygen deficiency itself kills without warning, and the %LEL sensor only reads validly once oxygen is confirmed present
  • B. Because H₂S is harmless and can be left until last
  • C. Because CO is measured in % by volume
  • D. Because the oxygen sensor is the slowest to respond
Answer: A — Because oxygen deficiency itself kills without warning, and the %LEL sensor only reads validly once oxygen is confirmed present
Oxygen is tested first because oxygen deficiency gives no warning and drops a person in seconds, and because the catalytic %LEL sensor only reads validly when enough oxygen is present to burn the sample. The order is oxygen, then flammable gas, then toxics such as H₂S and CO.

19. You bump-tested your gas detector this morning and it passed. Does that prove its readings are accurate?

  • A. Yes — a bump test is a field calibration
  • B. No — a bump test only proves the sensor responds and the alarm works; only calibration adjusts it to read the true value
  • C. Yes, provided the power-on self-test also passed
  • D. Yes, if the bump-test gas was in date
Answer: B — No — a bump test only proves the sensor responds and the alarm works; only calibration adjusts it to read the true value
A bump test is a functional pass/fail check that the sensor responds to gas and the alarm sounds. Calibration is a separate job: certified span gas is applied and the instrument adjusted so its displayed value is correct. A poisoned sensor can still self-test and zero perfectly, so only calibration proves accuracy.

20. Liquid LPG has splashed a crewman's glove and frozen it to his hand. He is in pain and the glove will not come off. What is the correct first aid?

  • A. Pull the glove off quickly before the cold spreads
  • B. Rub the hand briskly to restore the circulation
  • C. Cut around the glove, drench it with water, then re-warm gently with lukewarm water — never hot water, never rubbing
  • D. Thaw it rapidly under hot running water
Answer: C — Cut around the glove, drench it with water, then re-warm gently with lukewarm water — never hot water, never rubbing
Fabric frozen into the flesh must be cut around, not pulled (which strips the skin), and drenched with water first because dry gas-soaked cloth can throw a static spark. Re-warm slowly with lukewarm water — hot water scalds numb tissue, and rubbing tears the frozen cells apart.

21. Liquid ammonia has splashed a crewman's forearm and one eye. How does the correct treatment differ from that for a cryogenic (cold-burn) splash?

  • A. Both need slow re-warming with lukewarm water
  • B. Ammonia needs dry heat applied to the skin
  • C. Both require the affected part to be rubbed to disperse the chemical
  • D. Ammonia is a chemical burn — flush copiously for 15–20 minutes, shielding the unexposed eye; a cold burn is re-warmed gently, not flushed hard
Answer: D — Ammonia is a chemical burn — flush copiously for 15–20 minutes, shielding the unexposed eye; a cold burn is re-warmed gently, not flushed hard
Ammonia keeps burning while on the tissue, so it is flushed with plenty of water for 15–20 minutes and the unexposed eye is shielded from run-off. A cryogenic splash is instead re-warmed gently and never flushed hard or rubbed — doing the wrong one worsens the injury.

22. A cargo compressor room tests at 19% oxygen before entry. Why is a filter (canister) respirator forbidden, and what must be used?

  • A. A filter only cleans the air passing through it and cannot supply missing oxygen; a self-contained breathing apparatus is required
  • B. 19% is close enough to normal, so a filter respirator will do
  • C. The oxygen reading matters only for hydrocarbon testing
  • D. Only readings below 10% oxygen are actually dangerous
Answer: A — A filter only cleans the air passing through it and cannot supply missing oxygen; a self-contained breathing apparatus is required
A filter respirator removes specific contaminants but makes no oxygen, so it is useless where oxygen is deficient — and 19%, below the 19.5% minimum, means something is consuming the oxygen and the level may still be falling. Only a self-contained (or airline) breathing apparatus, carrying its own air, is acceptable.

23. An EEBD and an SCBA both supply breathing air. What is the essential difference that dictates how each may be used?

  • A. An EEBD carries much more air than an SCBA
  • B. An EEBD is a fixed constant-flow escape device (escape only); an SCBA is demand-fed and may be worked in
  • C. An SCBA must be fed by an airline from outside the space
  • D. They are interchangeable — grab whichever is nearest
Answer: B — An EEBD is a fixed constant-flow escape device (escape only); an SCBA is demand-fed and may be worked in
An EEBD delivers a fixed constant flow for a short fixed time and is for escape only — breathe harder than the flow and the hood collapses onto the face. An SCBA is demand-fed and may be used to enter, work and rescue, so you must never enter a space relying on an EEBD.

24. Under the IGC Code, a cargo presenting the greatest hazard — such as chlorine — must be carried on which ship type?

  • A. Type 3G — the least protection
  • B. Type 2G — as used for LNG
  • C. Type 1G — the greatest degree of protection and survivability
  • D. Type 2PG
Answer: C — Type 1G — the greatest degree of protection and survivability
Type 1G provides the greatest degree of protection for the most hazardous cargoes such as chlorine. LNG is carried on 2G ships and Type 3G is for the least hazardous gases; the IGC types a ship by the hazard of the cargo it may carry.

25. On a cargo liquid line where cryogenic liquid can be isolated between two closed valves, what must be fitted, and why?

  • A. A sample point, to check the cargo
  • B. A relief (safety) valve, because trapped cryogenic liquid warms, expands and can burst the line
  • C. A blank flange, to seal the line
  • D. A drain cock, to empty the line
Answer: B — A relief (safety) valve, because trapped cryogenic liquid warms, expands and can burst the line
Trapped cryogenic liquid warms, expands and generates enormous pressure — a hydraulic lock that ruptures the pipe — so every section that can be isolated must be relieved back to a tank or the vapour line. A sample point or drain cock gives no protection against that over-pressure.

26. Dry chemical powder knocks down a pressurised gas fire at the manifold. What essential follow-up action stops the fire simply re-igniting?

  • A. Isolate and stop the gas leak, and cool the surrounding steel with the water-spray/deluge system
  • B. Immediately open more cargo valves to bleed off the pressure
  • C. Apply large quantities of foam over the whole deck
  • D. Leave the leak flowing and douse the flame with a CO₂ extinguisher
Answer: A — Isolate and stop the gas leak, and cool the surrounding steel with the water-spray/deluge system
Dry powder breaks the flame chemically but gives no cooling and does not stop the leak; escaping gas re-ignites off hot steel. The source must be isolated and the hot metal kept cool with water spray. Bleeding more gas or leaving the leak flowing simply feeds the fire.

27. On a fully refrigerated LPG carrier the cargo tank pressure is slowly rising in transit. What is the cause, and the correct response?

  • A. The cargo is stratifying; circulate it with a pump
  • B. Air has leaked in; purge with nitrogen until the pressure falls
  • C. The relief valve is leaking by; open the vent riser
  • D. Heat leaking in warms the liquid and raises its vapour pressure (boil-off); run the reliquefaction plant to remove the heat
Answer: D — Heat leaking in warms the liquid and raises its vapour pressure (boil-off); run the reliquefaction plant to remove the heat
Heat leaks through the insulation, warming the liquid so its saturated vapour pressure — and thus the tank pressure — rises. The cure is to remove heat by reliquefying the boil-off and returning it as liquid, not to chase the gauge; venting is a last resort.

28. A ship comes out of dry-dock with her tanks full of fresh air. Which sequence correctly takes a tank from that condition to ready-to-load?

  • A. Inspect, inert, dry, gas up, cool down, load
  • B. Inspect, dry, inert, gas up, cool down, load
  • C. Inspect, dry, gas up, inert, cool down, load
  • D. Inspect, dry, inert, cool down, gas up, load
Answer: B — Inspect, dry, inert, gas up, cool down, load
Drying comes before inerting so residual water cannot freeze as ice or hydrates once the tank is cold, and cool-down comes after gassing up because the incondensable inert gas must be swept out first. Inerting before drying (option 0) is wrong — a wet inerted tank still ices up its valves and pump shafts at carriage temperature.

29. Your tanks are clean, dry and inerted with nitrogen and the terminal is ready. Why must you gas up with cargo vapour before you can take bulk liquid?

  • A. Because the oxygen left in the tank is still too high to load safely
  • B. Because the tank steel is still too warm to accept liquid cargo
  • C. Because inert gas is incondensable — its N₂ will not condense and its CO₂ freezes out, crippling the reliquefaction plant
  • D. Because the Gas Codes forbid loading into a nitrogen atmosphere
Answer: C — Because inert gas is incondensable — its N₂ will not condense and its CO₂ freezes out, crippling the reliquefaction plant
Nitrogen is far above its critical temperature at cargo conditions and any CO₂ freezes to dry ice, so both collect in the condenser as incondensables and stop the plant working; gassing up sweeps them out to about 90% cargo vapour. Oxygen (option 0) is already below 5% — that was the whole point of inerting — so it is not the obstacle.

30. Before bulk-loading LNG at about −162 °C, the tank is first sprayed with a little cargo liquid to cool it slowly. What are the two reasons for cooling down?

  • A. To avoid flash evaporation over-pressurising the tank and to limit thermal stress on the containment structure
  • B. To raise the tank pressure to the required loading value
  • C. To sweep out the last of the inert gas before liquid arrives
  • D. To expand the tank slightly so it holds more cargo
Answer: A — To avoid flash evaporation over-pressurising the tank and to limit thermal stress on the containment structure
Warm steel would flash the first bulk liquid into huge volumes of vapour — over-pressure and venting — and thermally shock the structure, so the tank is spray-cooled at roughly 10 °C per hour. Removing inert gas (option 2) is done during gassing up, a separate and earlier step, not during cool-down.

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