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CHEMCO exit exam questions and answers — Set 6 — Advanced Training for Chemical Tanker Cargo Operations

Set 6 of the Advanced Training for Chemical Tanker Cargo Operations (CHEMCO) exit exam bank — 30 of 663 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 6 — 30 CHEMCO exit exam questions with answers

1. Emergency alarm signals are provided on tankers in case of the following; which one of these alarms will be of major importance on a double-hull tankship with empty ballast tanks?

  • A. High concentration of toxic or flammable vapors
  • B. A discharge in engine-room or pumproom
  • C. When level of oxygen in inert gas entering tanks exceeds 5%
  • D. High level of oil residues in overboard discharge
Answer: A — High concentration of toxic or flammable vapors
On a double-hull tanker the empty ballast tanks surround the cargo tanks, so any leak from the cargo tanks can create toxic or flammable vapours in these spaces. SOLAS II-2 regulation 4.5.7 requires gas sampling of double-hull spaces, making high vapour concentration alarms the most important here.

2. While in port, if a fire occurs on board ship, support available from the shore includes the following; which one, in your opinion, makes the most important distinction for a shipboard fire?

  • A. Assistance from the fire brigade – experienced manpower and firefighting equipment.
  • B. Medical services of shore hospitals including ambulances with stretchers and paramedics in attendance, helicopters, etc.
  • C. Transportation for evacuating personnel from ship that are non-essential for firefighting.
  • D. Catering services where ship’s resources are restricted by the fire.
Answer: A — Assistance from the fire brigade – experienced manpower and firefighting equipment.
The most significant shore support for a shipboard fire in port is the fire brigade, which brings experienced firefighters and additional equipment beyond the ship's own resources. Medical, evacuation and catering support are useful but secondary to fighting the fire itself.

3. Typical Locations for High Sensitivity to Fatigue Failure The following areas are considered to be prone to fatigue failure on double hull oil tankers: which one is the most common

  • A. Side shell area below the load and ballast waterlines. These areas are subjected to the highest cycle loading through the ship’s life due to the passage of waves along the side of the ship.
  • B. Deck plating at connection to primary supporting members.
  • C. Connection between transverse bulkheads to the upper and lower bulkhead stools.
  • D. Connection between lower hopper sloping plating and inner bottom plating.
Answer: A — Side shell area below the load and ballast waterlines. These areas are subjected to the highest cycle loading through the ship’s life due to the passage of waves along the side of the ship.
On double-hull tankers the side shell area between the ballast and load waterlines experiences the highest number of cyclic loads from waves passing along the ship throughout its life, making it the most common location for fatigue cracking at longitudinal end connections.

4. Safeguards for Enclosed Space Entry; Before allowing access to the space, the responsible officer should ensure, amongst other things, that: identify the most important of all the elements

  • A. The personal protective equipment to be used by people entering the enclosed space must be prescribed.
  • B. Approved safety torches.
  • C. Approved UHF radio.
  • D. Personal gas detector or an area gas detector and alarm.
Answer: A — The personal protective equipment to be used by people entering the enclosed space must be prescribed.
Before entry the responsible officer must ensure the personal protective equipment for those entering is prescribed according to the hazards identified. This underpins the other safeguards and follows IMO Resolution A.1050(27) and ISGOTT enclosed space entry guidance.

5. In case of a collision, the following, amongst other steps are considered as a general plan of action; which one will be a priority in case of an underwater hull damage?

  • A. Assessing possible pollution due to rupture of fuel and or cargo (oil or chemical) tanks;
  • B. Taking corrective action to minimize the quantum of pollution; reporting the incident.
  • C. Assembling the emergency party.
  • D. Preparing for or implementing fire-fighting measures (in the event of a fire).
Answer: A — Assessing possible pollution due to rupture of fuel and or cargo (oil or chemical) tanks;
With underwater hull damage after a collision the priority is to assess possible pollution from ruptured fuel or cargo tanks, so that the extent of damage and spillage is known and the SOPEP or SMPEP response can be planned, along with stability and damage control.

6. The Medical First Aid Guide is published by the:

  • A. International Maritime Organisation
  • B. World Health Organisation
  • C. United Nations
  • D. International Labour Organisation
Answer: A — International Maritime Organisation
The Medical First Aid Guide for Use in Accidents Involving Dangerous Goods (MFAG) is published by IMO (developed jointly with WHO and ILO).

7. Find a statement that in your opinion, is the most critical in a grounding incident?

  • A. Grounding can cause loss of human life.
  • B. Grounding can cause harmful environmental impact, especially in the case where large tanker ships are involved.
  • C. Grounding can cause financial consequences to local communities close to the accident.
  • D. Grounding can cause financial consequences to ship- owners, due to ship loss or penalties.
Answer: A — Grounding can cause loss of human life.
The loss of human life is the most critical consequence of any grounding, because safety of life is the overriding priority under SOLAS and the ISM Code. Environmental and financial impacts are serious but secondary.

8. Safeguards for Enclosed Space Entry; Before allowing access to the space, the responsible officer should ensure, amongst other things, that: identify the most important of all the elements

  • A. A rescue harness, complete with lifeline, is ready for immediate use at the entrance to the space.
  • B. Fully charged safety torch is ready for immediate use at the entrance to the space.
  • C. A responsible member of the crew is in constant attendance outside the enclosed space, in the immediate vicinity of the entrance and in direct contact with a responsible officer.
  • D. These persons should be trained in the actions to be taken in the event of an emergency.
Answer: C — A responsible member of the crew is in constant attendance outside the enclosed space, in the immediate vicinity of the entrance and in direct contact with a responsible officer.
A responsible crew member in constant attendance at the entrance, in direct contact with the responsible officer, is essential so that any emergency inside is detected immediately and the alarm raised. This attendant is required by IMO Resolution A.1050(27) and ISGOTT.

9. Statements on Boiler: identify a statement that supports the use of a watertube boiler with a superheater in many tanker vessels?

  • A. The boiler on a tanker vessel is equally important as the main propulsion engines
  • B. On a large oil tanker, the fuel consumption in the boiler could be as high as 2/3rd of the engines.
  • C. Without having steam at superheated condition, you may not be able to operate the cargo pump turbines efficiently and safely
  • D. Without having steam, you may not be able to maintain the oil temperatures correctly within the cargo tanks for discharging.
Answer: C — Without having steam at superheated condition, you may not be able to operate the cargo pump turbines efficiently and safely
Many tankers have steam turbine-driven cargo pumps, which need superheated steam to operate efficiently and safely without condensation and erosion in the turbine. This is why watertube boilers with superheaters are fitted on such vessels.

10. Which function is NOT provided by the scrubber of an inert gas system?

  • A. Cools the inert gas.
  • B. Removes particulate matter like soot.
  • C. Maintains gas pressure in the tanks.
  • D. Removes chemical impurities from the gas.
Answer: C — Maintains gas pressure in the tanks.
The IG scrubber cools the flue gas, removes soot and particulate matter, and washes out sulphur dioxide and other chemical impurities. It does not maintain gas pressure in the tanks; that is done by the blowers and the pressure regulating valve.

11. Introducing inert gas into a tank already inert with the object of further reducing the oxygen or hydrocarbon content to prevent combustion if air enters the tank is called

  • A. purging
  • B. gas freeing
  • C. gas dispersion
  • D. bonding
Answer: A — purging
ISGOTT defines purging as introducing inert gas into a tank that is already inert, to further reduce the oxygen and hydrocarbon content so that when air is later introduced for gas freeing, no part of the tank atmosphere passes through the flammable range.

12. Typically nitrogen contained in inert gas generated from boiler flue gas, at the scrubber outlet is

  • A. 50%
  • B. 60%
  • C. 70%
  • D. 83%
Answer: D — 83%
Typical inert gas from boiler flue gas at the scrubber outlet consists of about 83% nitrogen, 12 to 14% carbon dioxide, 2 to 4% oxygen, with small amounts of water vapour and sulphur dioxide, as given in ISGOTT and the IMO IG guidelines.

13. Which statement about inert gas pressures in a cargo tank is TRUE?

  • A. The pressures of the inert gas in the tank may create excessive pressure at the pump while discharging.
  • B. Gas pressures should be maintained at the highest permissible level throughout the discharging process.
  • C. High gas pressures may cause pyrophoric oxidation in the tank.
  • D. High gas pressures may cause loss of suction when stripping.
Answer: B — Gas pressures should be maintained at the highest permissible level throughout the discharging process.
During discharge the inert gas pressure should be kept as high as is permissible, so that as cargo is pumped out the tanks never approach a vacuum or allow air ingress. Maintaining positive pressure also helps pump suction, as recommended in ISGOTT.

14. The purpose of the deck seal in an inert gas system is to prevent

  • A. flammable vapors from entering machinery space
  • B. flue gas escaping to atmosphere
  • C. inert gas escaping to atmosphere
  • D. air entering inert gas system
Answer: A — flammable vapors from entering machinery space
The deck water seal prevents the back flow of hydrocarbon vapours from the cargo tanks through the IG main to the IG plant and the machinery space, which would otherwise create a serious fire hazard. The FSS Code chapter 15 requires it as the main non-return device.

15. After the initial cleaning of flue gas in an inert gas system the gas is passed through what device for final cleaning?

  • A. Scrubber
  • B. Demister
  • C. Deck water seal
  • D. Final filter
Answer: B — Demister
After the scrubber has cooled and washed the flue gas, it passes through a demister, which removes entrained water droplets and remaining fine particles before the gas reaches the blowers and the deck main.

16. The "flammable limits" of an atmosphere are the

  • A. two temperatures between which an atmosphere will self ignite
  • B. upper and lower percentage of vapor concentrations in an atmosphere which will burn if an ignition source is present
  • C. upper and lower pressures between which an atmosphere will not burn
  • D. two temperatures between which an atmosphere will burn if an ignition source is present
Answer: B — upper and lower percentage of vapor concentrations in an atmosphere which will burn if an ignition source is present
Flammable limits are the lower and upper percentages by volume of vapour in air between which the mixture will burn if an ignition source is present. Below the lower limit the mixture is too lean and above the upper limit too rich.

17. Flue gas is drawn from the boiler uptake and delivered to the inert gas scrubber by a:

  • A. Exhaust gas pressure from the stack
  • B. High capacity fan
  • C. Inert gas compressor
  • D. Natural aspiration
Answer: B — High capacity fan
In a flue gas IG system high capacity fans, the IG blowers, draw gas from the boiler uptake through the scrubber and deliver it under pressure to the deck main and cargo tanks. Stack pressure alone is insufficient.

18. What is the major function of the deck water seal in an inert gas system?

  • A. Relieves excessive pressures from the system.
  • B. Isolates hazardous areas from nonhazardous areas.
  • C. Prevents the flow of inert gas into closed or isolated tanks.
  • D. Removes any leftover water or soot after the gas has been scrubbed.
Answer: B — Isolates hazardous areas from nonhazardous areas.
The deck water seal forms a gas-tight barrier between the hazardous cargo area and the non-hazardous IG plant and machinery spaces, preventing back flow of hydrocarbon gas while allowing inert gas to pass forward to the tanks.

19. Inert gas systems must be capable of delivering inert gas with an oxygen content by volume in the inert gas main of not more than

  • A. 2%
  • B. 5%
  • C. 8%
  • D. 11%
Answer: B — 5%
The FSS Code chapter 15 requires the inert gas system to be capable of delivering inert gas with an oxygen content of not more than 5% by volume in the IG supply main at the required rate.

20. On a hydrocarbon flammability chart the line which extends from 0% to 21.8% oxygen, lying tangent to the flammability range, is called the

  • A. minimum oxygen content line upper threshold limit
  • B. critical displacement line
  • C. critical dilution line
  • D. upper threshold limit
Answer: C — critical dilution line
On the flammability diagram the critical dilution line runs from pure air at 21% oxygen tangent to the flammable zone. Mixtures on the inert side of this line can be diluted with air without passing through the flammable range, which is the basis of purging before gas freeing in ISGOTT.

21. The component in an inert gas system used for cleaning the gas of solid and sulfur combustion products, while simultaneously cooling the inert gas, is called the

  • A. filter
  • B. cooler
  • C. scrubber
  • D. purifier
Answer: C — scrubber
The scrubber washes the flue gas with seawater, removing soot and sulphur combustion products while simultaneously cooling the gas to near seawater temperature before it passes to the demister and blowers.

22. Inert gas systems must be capable of maintaining inert gas with an oxygen content by volume in the cargo tanks of not more than

  • A. 2%
  • B. 5%
  • C. 8%
  • D. 11%
Answer: C — 8%
SOLAS II-2 regulation 4.5.5 and the FSS Code chapter 15 require the inert gas system to maintain the atmosphere in any part of the cargo tanks at an oxygen content of not more than 8% by volume and at a positive pressure.

23. You are discharging cargo and the inert gas system is in operation to inert the tanks. The pressure in a tank being discharged starts to drop below the allowable limit. What action should you take?

  • A. Cut in another IG fan to increase gas flow.
  • B. Open the pressure control valve until the pressure increases.
  • C. Open the tank isolation valve to the fully open position.
  • D. Reduce the pumping rate.
Answer: B — Open the pressure control valve until the pressure increases.
If tank pressure falls during discharge, the pressure control valve should be opened to increase the flow of inert gas into the deck main and restore positive pressure. If this is insufficient, the discharge rate must then be reduced.

24. The fresh air intake of the inert gas system

  • A. prevents the flue gas from falling below an oxygen content of 3%
  • B. allows the inert gas piping to be used for gas freeing the tanks
  • C. opens when there is excessive vacuum on the deck water seal
  • D. enables outside air to mix with and to cool the hot flue gasses
Answer: B — allows the inert gas piping to be used for gas freeing the tanks
The fresh air intake allows the IG blowers to deliver fresh air through the IG main and distribution piping to the cargo tanks, so the same system can be used for gas freeing after purging, as provided in FSS Code chapter 15.

25. What is the maximum oxygen content below which flaming combustion will no longer occur?

  • A. 5%
  • B. 8%
  • C. 10%
  • D. 12%
Answer: B — 8%
SOLAS and the FSS Code take 8% oxygen by volume as the level below which a tank atmosphere is considered inert and flaming combustion of hydrocarbon gas will not occur, which includes a safety margin below the theoretical 11% limit given in ISGOTT.

26. In which of the following conditions, the IG blower fans should shut down automatically?

  • A. Oxygen content above 8%
  • B. Low water level in deck seal
  • C. Low water level in the scrubber tower
  • D. High scrubber water level
Answer: D — High scrubber water level
The FSS Code chapter 15 requires the IG blowers and gas regulating valve to shut down automatically on high water level in the scrubber, to prevent water being carried over into the blowers and deck main, as well as on low scrubber water supply.

27. What type of liquid is used in the liquid P/V breaker?

  • A. Hydraulic oil
  • B. Water-antifreeze mixture
  • C. Distilled water
  • D. Oil from the cargo
Answer: B — Water-antifreeze mixture
A liquid-filled P/V breaker is filled with a water and antifreeze mixture, typically glycol, so that the liquid seal does not freeze in cold weather and continues to protect the tanks against excessive pressure or vacuum.

28. What is the maximum percent of oxygen, by volume, allowed to be maintained in the cargo tanks prior to the commencement of crude oil tank washing?

  • A. 5%
  • B. 8%
  • C. 10%
  • D. 12%
Answer: B — 8%
MARPOL Annex I and the IMO COW specifications require the oxygen content of each tank to be crude oil washed to be not more than 8% by volume, and the tank to be at positive pressure, before washing begins.

29. Checks to be done, amongst others, before and during COW are listed; identify the most important safety check

  • A. When carrying out crude oil washing during cargo discharge, the Master should inform the terminal competent authority 24 hours before commencement (or other ship when ship-to-ship transfer is involved)
  • B. The Oxygen analyzing equipment to be tested and working satisfactorily
  • C. Inert gas in tank to be checked – (Oxygen to be less than 8%), IG pressure to be satisfactory (positive pressure)
  • D. All hydrant valves on the tank washing line to be shut
Answer: C — Inert gas in tank to be checked – (Oxygen to be less than 8%), IG pressure to be satisfactory (positive pressure)
The most important safety check before and during COW is confirming that the tank to be washed is inerted with oxygen below 8% by volume and at positive IG pressure, as required by MARPOL Annex I regulation 35 and the COW specifications, since washing generates static electricity.

30. Concurrent COW with cargo discharge: identify the precaution for the Concurrent COW method for use

  • A. COW concurrent method utilizes the crude oil stream being discharged, together with its associated back pressure, to supply the COW pipeline with crude oil.
  • B. COW concurrent method can be achieved either by a "bleed-off' system from the main crude oil discharge pipelines for supply to the COW pipeline or by separate supply using a designated cargo pump.
  • C. COW concurrent method: The normal minimum back pressure required for the operation of the COW guns is 8 kg/cm2.
  • D. COW concurrent method: If supply is achieved by the bleed-off from the bulk discharge, then sufficient back pressure has to be maintained at all times.
Answer: C — COW concurrent method: The normal minimum back pressure required for the operation of the COW guns is 8 kg/cm2.
For concurrent COW the washing machines need a sufficient back pressure to work effectively, and the normal minimum required at the COW guns is about 8 kg/cm2. If this pressure is not maintained the washing will be ineffective.

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