Skip to content
DG Exit Exam
Home OCTCO/OCTF sets
Answer Key

OCTCO/OCTF exit exam questions and answers — Set 13 — Oil and Chemical Tanker Cargo Operations

Set 13 of the Oil and Chemical Tanker Cargo Operations (OCTCO/OCTF) exit exam bank — 30 of 802 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.

Bank last rebuilt .

Practise these OCTCO/OCTF questions OCTCO/OCTF mock exit exam, 30 marks OCTCO/OCTF exit exam sets and syllabus

30 of 30 shown · Set 13

Nothing in this set matches that. Try a shorter word, or search the whole key.

Set 13 — 30 OCTCO/OCTF exit exam questions with answers

1. After the flue gas has been scrubbed of particulate matter and sulphurous gases, it still contains ____, which must be removed.

  • A. Ash
  • B. Water droplets
  • C. Acid
  • D. None of these
Answer: B — Water droplets
Gas leaving the scrubber carries entrained water droplets from the sea water sprays. Demisters (mesh or cyclone type) at the scrubber outlet remove this moisture before the gas reaches the blowers, preventing corrosion and deposits downstream.

2. What is the full form of IAPH?

  • A. International Association of Ports and Harbors
  • B. International Association of Principal and Hull
  • C. International Association of Pump Pressure Head
  • D. None of the above
Answer: A — International Association of Ports and Harbors
IAPH is the International Association of Ports and Harbors. Together with ICS and OCIMF it co-publishes ISGOTT, including the Ship/Shore Safety Checklist used at tanker terminals.

3. An oil with an electrical conductivity greater than 50 picosiemens/metre (pS/m), which renders it incapable of retaining a significant electrostatic charge, is called

  • A. A static non-accumulator oil
  • B. A static accumulator oil
  • C. An electrical non-conductor
  • D. None of the above
Answer: A — A static non-accumulator oil
ISGOTT classes oils with conductivity above 50 pS/m as non-accumulators, because charge relaxes quickly. Oils below 50 pS/m, such as many clean products, are static accumulators and need precautions like reduced initial loading rates.

4. Steam heating coils are provided in some cargo tanks to

  • A. Provide warm water for tank cleaning
  • B. Reduce the volume of cargo in the tank
  • C. Increase the volume of cargo in the tank
  • D. Heat cargoes which have a high viscosity or pour point
Answer: D — Heat cargoes which have a high viscosity or pour point
Heating coils keep cargoes such as heavy fuel oil, waxy crude or vegetable oils above their pour point and at a viscosity low enough to pump, preventing solidification and ensuring complete discharge.

5. What is putrefaction?

  • A. Decomposition of most animal and vegetable oils over time in storage
  • B. Decomposition of most mineral oils over time when heated
  • C. Decomposition of most animal and vegetable oils only when heated
  • D. A process that applies to all mineral and vegetable oils carried on tankers
Answer: A — Decomposition of most animal and vegetable oils over time in storage
Putrefaction is the biological decomposition of animal and vegetable (organic) oils over time in storage, producing toxic gases like hydrogen sulphide and depleting oxygen. Mineral oils do not putrefy in this way.

6. Cargo pump rooms are fitted with

  • A. One fan for ventilation
  • B. Portable water sprinklers for fire fighting
  • C. A fixed fire extinguishing system
  • D. One fan for exhaust
Answer: C — A fixed fire extinguishing system
SOLAS II-2/10.9 requires each cargo pump room on tankers to have a fixed fire-extinguishing system, such as CO2, high-expansion foam or water spray, operated from a readily accessible position outside the pump room.

7. What is the flammable range?

  • A. Vapour concentration range between the LEL and UEL
  • B. Vapour concentration below the LEL
  • C. Vapour concentration above 1% by volume
  • D. Vapour concentration above the UEL
Answer: A — Vapour concentration range between the LEL and UEL
The flammable range is the span of hydrocarbon gas concentrations in air between the lower and upper flammable limits. Below the LEL the mixture is too lean and above the UEL too rich to burn.

8. Chemicals used for clean-up of a deck spill must not be allowed to enter the water when the ship is in port

  • A. Unless approved chemicals are used for the clean-up operation
  • B. Unless authorised by the master of the ship
  • C. Unless authorised by the ship manager
  • D. Unless permission has been obtained from the harbour authorities
Answer: D — Unless permission has been obtained from the harbour authorities
Dispersants and cleaning chemicals can themselves pollute. In port waters their discharge falls under local jurisdiction, so they may enter the water only with prior permission of the harbour or port authority.

9. While using a combustible gas indicator, if the hydrocarbon content of the atmosphere exceeds the UEL, the needle of the indicator will

  • A. Move to the maximum reading and immediately return to zero
  • B. Remain at zero without moving
  • C. Move halfway up the scale
  • D. Move to the maximum reading and stay there
Answer: A — Move to the maximum reading and immediately return to zero
In a catalytic-filament indicator, a sample above the UEL first passes through the flammable range, so the needle swings to full scale, then the over-rich mixture cannot burn on the filament and the reading drops back to zero.

10. The fresh air intake of the inert gas system

  • A. Opens when there is excessive vacuum on the deck water seal
  • B. Prevents the flue gas from falling below an oxygen content of 3%
  • C. Allows the inert gas piping to be used for gas freeing
  • D. Enables outside air to mix with and cool the hot flue gases
Answer: C — Allows the inert gas piping to be used for gas freeing
A fresh air inlet, with blanking arrangements, lets the IG blowers draw atmospheric air and deliver it through the IG main to the cargo tanks, so the system can be used for gas freeing after inert operations.

11. Combustible gas indicators operate by drawing an air sample into the instrument

  • A. Where its specific gravity is measured
  • B. Where it is mixed with nitrogen
  • C. Where it is ignited by a sparking device
  • D. Over an electrically heated platinum filament
Answer: D — Over an electrically heated platinum filament
The catalytic (Wheatstone bridge) explosimeter passes the sample over a heated platinum filament. Combustion on the filament changes its resistance, unbalancing the bridge, and the meter reads this as a percentage of the LEL.

12. The average flammable (explosive) range of petroleum vapours mixed with air is

  • A. 0% to 1%
  • B. 1% to 10%
  • C. 12% to 20%
  • D. 10% to 15%
Answer: B — 1% to 10%
ISGOTT gives the typical flammable range for petroleum gas mixtures in air as roughly 1% to 10% hydrocarbon by volume. Below about 1% the mixture is too lean and above about 10% too rich to burn.

13. The Oil Record Book Part I shall be retained on board for a period of

  • A. 1 year after the last entry has been made
  • B. 1 year after the first entry has been made
  • C. 3 years after the last entry has been made
  • D. 3 years after the first entry has been made
Answer: C — 3 years after the last entry has been made
MARPOL Annex I Regulation 17 requires the Oil Record Book to be kept readily available for inspection and retained on board for three years after the last entry has been made.

14. You are planning to use the crude oil washing system. What precaution must be taken with the source tank for the washing machines?

  • A. The oil in the source tank must be sampled for compatibility
  • B. At least one metre must be decanted from the source tank
  • C. The inert gas system must lower the oxygen content in the source tank to a maximum of 12%
  • D. The source tank must have been crude oil washed at least once in the past 150 days
Answer: B — At least one metre must be decanted from the source tank
Water settles at the bottom of cargo tanks. Decanting at least one metre from a tank before using it as a COW source removes this water layer, so the washing medium is dry crude and static generation from water in the wash is avoided.

15. The fitting at the end of a cargo line in a tank that allows suction to be taken close to the bottom of the tank is a

  • A. Vacuum valve
  • B. Bell-mouth
  • C. Strainer
  • D. Suction end
Answer: B — Bell-mouth
A bell-mouth is the flared open end of a cargo suction line positioned just above the tank bottom. Its shape reduces entry velocity and turbulence and allows the tank to be stripped to a low level.

16. Ballast water exchange should be done at least ____ NM from the nearest land and in waters at least ____ metres in depth.

  • A. 100 NM and 200 metres
  • B. 100 NM and 100 metres
  • C. 200 NM and 200 metres
  • D. 200 NM and 100 metres
Answer: C — 200 NM and 200 metres
Regulation B-4 of the BWM Convention requires exchange, wherever possible, at least 200 nautical miles from the nearest land in water at least 200 metres deep; where not possible, at least 50 NM and 200 m depth.

17. In a centrifugal pump,

  • A. The fluid moves in a direction opposite to the impeller rotation
  • B. The width of the discharge pipeline decreases outwards
  • C. The fluid moves in the same direction as the impeller rotation
  • D. The discharge side has a negative pressure
Answer: C — The fluid moves in the same direction as the impeller rotation
The rotating impeller imparts velocity to the liquid, flinging it outward in the direction of rotation into the volute, where velocity is converted to pressure. The suction eye, not the discharge, is at low pressure.

18. Calorific value is the quantity of heat ____ when a unit quantity of fuel is burnt completely.

  • A. Observed
  • B. Released
  • C. Consumed
  • D. Required
Answer: B — Released
Calorific value is the heat energy released by complete combustion of a unit mass or volume of fuel, expressed for example in kJ/kg. It indicates the energy content of the fuel.

19. Deficient oxygen content inside a confined space can be detected with

  • A. Litmus paper
  • B. A combustible gas indicator
  • C. An oxygen breathing apparatus
  • D. An oxygen detector
Answer: D — An oxygen detector
Only an oxygen analyser or detector measures oxygen concentration directly. Before entry the atmosphere must read 21% oxygen by volume; a combustible gas indicator measures hydrocarbons and litmus paper only indicates acidity.

20. Each inert gas system gas main must have an automatic shut-down valve at the outlet of the gas production plant. This valve must close automatically upon

  • A. Blower failure
  • B. Cargo pump failure
  • C. Deck seal low water level
  • D. Low inert gas temperature
Answer: A — Blower failure
The FSS Code requires the gas regulating valve to close automatically on failure of the IG blowers, so that no air or hydrocarbon gas can flow back towards the plant and machinery spaces.

21. A self-contained breathing apparatus is used to

  • A. Make underwater repairs to barges
  • B. Enter areas that may contain dangerous fumes or lack oxygen
  • C. Determine if the air in a tank is safe for men
  • D. Resuscitate an unconscious person
Answer: B — Enter areas that may contain dangerous fumes or lack oxygen
SCBA supplies breathing air from a cylinder independent of the surrounding atmosphere, allowing entry into toxic, smoke-filled or oxygen-deficient spaces for rescue or emergencies. It does not test atmospheres or resuscitate casualties.

22. What is the other name for paraffin hydrocarbons?

  • A. Naphthalene
  • B. Propane
  • C. Cycloparaffin
  • D. Alkane
Answer: D — Alkane
Paraffins are saturated straight or branched chain hydrocarbons with the general formula CnH2n+2, known chemically as alkanes. Cycloparaffins (naphthenes) are ring compounds and naphthalene is an aromatic.

23. What should cargo sample lockers be constructed of?

  • A. Stainless steel only
  • B. Material fully resistant to the cargoes sampled
  • C. Wood
  • D. Neoprene
Answer: B — Material fully resistant to the cargoes sampled
The IBC Code requires cargo samples to be stowed in a designated space in the cargo area, in lockers made of material resistant to the cargoes they hold, so that leakage cannot attack the locker and spread.

24. An inert gas system should be used to

  • A. Prevent fires in pump rooms
  • B. Keep the cargo tank free (ullage) space inerted
  • C. Blow through the cargo lines
  • D. Keep the whole cargo area inerted
Answer: B — Keep the cargo tank free (ullage) space inerted
The IGS supplies low-oxygen gas to the ullage space of cargo tanks, keeping it below 8% oxygen and under positive pressure so the tank atmosphere cannot become flammable. It does not inert pump rooms or open deck areas.

25. A build-up of wet solids on the IG blower impeller blade tips indicates a problem with the

  • A. Baffles
  • B. Demister
  • C. Deck seal
  • D. None of the above
Answer: B — Demister
If the demister is damaged or choked, water carry-over with soot passes to the blower, depositing wet solids on impeller tips. This causes imbalance and vibration, so the demister should be inspected and cleaned.

26. A large spill of LPG will be visible as a ____ of condensed water vapour.

  • A. White cloud
  • B. Blue cloud
  • C. Black cloud
  • D. None of these
Answer: A — White cloud
Spilled LPG evaporates rapidly and chills the surrounding air below its dew point, condensing atmospheric moisture into a visible white cloud. The flammable vapour may extend beyond the visible cloud.

27. Which of the following statements is NOT true with regard to a chemical tanker pump room?

  • A. Pump discharge pressures can be read from outside the pump room
  • B. The pump room bilge system can be operated from outside the pump room
  • C. Ladders for normal access should not be vertical and should have platforms
  • D. Rescue equipment for hoisting an injured person should be kept in the deck store
Answer: D — Rescue equipment for hoisting an injured person should be kept in the deck store
The IBC Code requires pump room rescue arrangements to allow a casualty to be hoisted out without delay, so the hoisting equipment and stretcher must be at or near the pump room entrance, not stored away in the deck store.

28. The ring main pipeline system is extensively used on

  • A. VLCCs
  • B. Crude oil tankers
  • C. Medium range tankers
  • D. Product carriers
Answer: D — Product carriers
A ring main system gives great flexibility, allowing several grades to be handled and segregated with many valves. This suits product carriers carrying multiple parcels, while large crude carriers use simpler direct line or free-flow systems.

29. What safety margin of tank volume is allowed when calculating the filling ratio of a cargo that needs heating during carriage?

  • A. 5% of the tank capacity
  • B. 10% of the cargo capacity
  • C. 2% of the tank capacity
  • D. 1% of the tank capacity
Answer: C — 2% of the tank capacity
Tanks are generally not filled beyond 98% at the highest temperature the cargo will reach. For a heated cargo the loading ullage is calculated so that, after thermal expansion, a 2% margin of tank capacity remains.

30. Submersible pumps found in chemical tankers are normally made of

  • A. Aluminium alloy
  • B. Fibre
  • C. Stainless steel
  • D. Nickel alloy
Answer: C — Stainless steel
Chemical tankers carry corrosive and high-purity cargoes, so deepwell and submerged cargo pumps are normally made of stainless steel, which resists a wide range of chemicals and is easy to clean between grades.

Printing this? Use your browser's Print (Ctrl/⌘ + P) — the buttons, the search box and the site chrome drop out and the questions run on as plain text, so a set fits a few pages. Filter to one set first if you only want that set on paper.

Practise these OCTCO/OCTF questions as a timed paper All 802 OCTCO/OCTF questions and answers OCTCO/OCTF exit exam sets and syllabus All 24 STCW exit exam courses

Send this OCTCO/OCTF answer key to your batch

Send on WhatsApp

More free tools for seafarers

Mariners DigestBrief for seafarers, Tue–SatSIRE PRO: Ship InspectionTanker inspection prepRightShip ProRISQ 3.2 dry-cargo inspection prepCOLREGS ReaderRules of the road, read aloud