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CHEMCO exit exam questions and answers — Set 19 — Advanced Training for Chemical Tanker Cargo Operations

Set 19 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 19 — 30 CHEMCO exit exam questions with answers

1. How is the ship's vapour manifold connection identified to prevent it being confused with a liquid cargo connection?

  • A. Painted red/yellow/red bands with the word VAPOUR stencilled near the flange
  • B. Painted entirely green with an arrow
  • C. Fitted with a blue flange only
  • D. Marked only on the cargo plan
Answer: A — Painted red/yellow/red bands with the word VAPOUR stencilled near the flange
Under IMO vapour emission control guidance and OCIMF recommendations, the vapour manifold is marked with yellow and red bands and the word VAPOUR, and is fitted with a stud to prevent a liquid hose being connected to it by mistake.

2. During discharge of a cargo with a hydraulically driven submerged pump, which reading on the cofferdam purging of the pump indicates a possible cargo seal leak?

  • A. Cargo liquid or vapour found when the pump cofferdam is purged
  • B. Hydraulic oil pressure steady at the normal working value
  • C. Normal discharge pressure at the manifold
  • D. Ambient temperature in the cargo control room
Answer: A — Cargo liquid or vapour found when the pump cofferdam is purged
Submerged hydraulic pumps have a cofferdam between the cargo seal and hydraulic seal. Regular purging of this cofferdam, before and after operations, reveals cargo or hydraulic oil leakage early so that the pump can be repaired before cargo contaminates the hydraulic system or vice versa.

3. For a heated cargo, why is the cargo temperature monitored and recorded at regular intervals during the voyage?

  • A. To keep it within the shipper's limits and the coating and adjacent cargo limits
  • B. To calculate the ship's fuel consumption
  • C. To check the accuracy of the ullage tape only
  • D. To decide the ballast water exchange sequence
Answer: A — To keep it within the shipper's limits and the coating and adjacent cargo limits
Overheating can damage coatings, trigger polymerisation or affect adjacent heat-sensitive cargoes, while underheating can allow cargo to solidify. Regular monitoring and records of cargo temperature show that heating instructions were followed and protect the ship in claims.

4. What should be done before cargo operations start regarding the emergency shutdown arrangements between ship and shore?

  • A. Test the ESD system and agree its activation method and closure times
  • B. Disconnect the ESD link to avoid spurious trips
  • C. Leave the ESD for the terminal to operate alone
  • D. Test the ESD only after the first hour of loading
Answer: A — Test the ESD system and agree its activation method and closure times
The ship/shore safety checklist requires the emergency shutdown procedures and system to be agreed and tested before transfer begins, including how each side will activate it and valve closure times, so that flow can be stopped safely in an emergency.

5. Which action is appropriate when the cargo tank high-level alarm sounds unexpectedly during loading?

  • A. Stop or divert the flow to that tank immediately and verify the level by an independent means
  • B. Silence the alarm and continue at the same rate
  • C. Increase the loading rate to finish the tank sooner
  • D. Open the tank's ullage port to relieve pressure
Answer: A — Stop or divert the flow to that tank immediately and verify the level by an independent means
A high-level alarm means the tank is approaching its filling limit. The flow to that tank must be stopped or diverted at once and the actual level checked independently before resuming, since a faulty gauge may already have allowed the tank to fill beyond its planned ullage.

6. What does the oxygen analyser on a nitrogen-padded chemical tank help to confirm?

  • A. That the oxygen content in the ullage space remains below the required level
  • B. That the cargo has not polymerised
  • C. That the cargo density is within specification
  • D. That the tank coating is intact
Answer: A — That the oxygen content in the ullage space remains below the required level
When a cargo requires inerting or padding, the ullage space oxygen level must be monitored to show that the nitrogen blanket is effective, preventing a flammable atmosphere or oxidation of air-sensitive cargoes. The readings should be recorded.

7. What is the purpose of a tank pressure monitoring system on a chemical tanker fitted with closed venting?

  • A. To give early warning of over-pressure or vacuum before P/V valves lift or the tank is damaged
  • B. To measure cargo density
  • C. To indicate the remaining stripping quantity
  • D. To show the hydraulic oil pressure of the pump
Answer: A — To give early warning of over-pressure or vacuum before P/V valves lift or the tank is damaged
Closed loading and discharging can quickly raise or lower tank pressure. Pressure monitoring with alarms allows the operator to adjust rates, vapour return or nitrogen supply before the pressure/vacuum valves lift or the tank structure is overstressed.

8. Which functional group is characteristic of alcohols such as methanol and ethanol?

  • A. Hydroxyl group (-OH)
  • B. Carbonyl group within a carbon chain (C=O)
  • C. Carboxyl group (-COOH)
  • D. Amino group (-NH2)
Answer: A — Hydroxyl group (-OH)
Alcohols contain the hydroxyl (-OH) group attached to a carbon atom. Ketones contain a carbonyl group, organic acids a carboxyl group and amines an amino group. The functional group largely determines the cargo's reactivity and compatibility.

9. Acetone and methyl ethyl ketone belong to which chemical group?

  • A. Ketones
  • B. Esters
  • C. Alcohols
  • D. Aldehydes
Answer: A — Ketones
Acetone and methyl ethyl ketone (MEK) are ketones, containing a carbonyl group bonded to two carbon atoms. They are widely used industrial solvents and are aggressive to some tank coatings, so coating resistance lists must be checked.

10. Benzene, toluene and xylene are classified as:

  • A. Aromatic hydrocarbons
  • B. Aliphatic alcohols
  • C. Glycols
  • D. Inorganic acids
Answer: A — Aromatic hydrocarbons
Benzene, toluene and xylene are aromatic hydrocarbons, built on the benzene ring. They are flammable, mostly insoluble in water and float on it, and have toxic effects; benzene is a recognised human carcinogen.

11. Why does methanol present a particular hazard when it burns?

  • A. It burns with a nearly invisible flame in daylight
  • B. It cannot be extinguished by any foam
  • C. It produces large quantities of black smoke
  • D. It explodes on contact with water
Answer: A — It burns with a nearly invisible flame in daylight
Methanol burns with a pale blue flame that is very hard to see in daylight, so a fire may go unnoticed and people may walk into it. Thermal imaging or heat detection is useful, and alcohol-resistant foam or water is used because methanol is water-miscible.

12. Approximately what is the relative density of concentrated (about 98%) sulphuric acid?

  • A. 1.83
  • B. 1.03
  • C. 0.79
  • D. 1.25
Answer: A — 1.83
Concentrated sulphuric acid has a relative density of about 1.83, nearly twice that of water. Such high-density cargoes usually cannot fill a tank completely without exceeding its design loading, which limits filling heights and must be checked against the loading manual.

13. Under MARPOL Annex II, a high-viscosity substance is a Category X or Y noxious liquid substance with a viscosity at the unloading temperature of:

  • A. 50 mPa·s or more
  • B. 5 mPa·s or more
  • C. 20 mPa·s or more
  • D. 500 mPa·s or more
Answer: A — 50 mPa·s or more
MARPOL Annex II regulation 1 defines a high-viscosity substance as a Category X or Y NLS with a viscosity of 50 mPa·s or more at the unloading temperature. Such substances require a prewash before the ship leaves the port of unloading.

14. Under MARPOL Annex II, a substance with a melting point below 15°C is a solidifying substance if, at the time of unloading, its temperature is:

  • A. Less than 5°C above its melting point
  • B. Less than 10°C above its melting point
  • C. More than 15°C above its melting point
  • D. Below 0°C
Answer: A — Less than 5°C above its melting point
MARPOL Annex II regulation 1 defines a solidifying substance as one with a melting point below 15°C that is less than 5°C above its melting point at unloading, or one with a melting point of 15°C or more that is less than 10°C above its melting point at unloading.

15. Paraffin wax has a melting point well above 15°C. Under MARPOL Annex II it is treated as a solidifying substance at unloading if its temperature then is:

  • A. Less than 10°C above its melting point
  • B. Less than 5°C above its melting point
  • C. Less than 2°C above its melting point
  • D. Exactly at its boiling point
Answer: A — Less than 10°C above its melting point
For a noxious liquid substance with a melting point of 15°C or above, MARPOL Annex II regulation 1 treats it as solidifying when its unloading temperature is less than 10°C above the melting point. The margin is 5°C for substances melting below 15°C.

16. Most chemical cargo vapours have a vapour density greater than 1. What is the practical consequence on deck and in enclosed spaces?

  • A. Vapours tend to sink and collect in low points such as pump room bilges and under decks
  • B. Vapours rise rapidly and disperse above the masthead
  • C. Vapours are always harmless once released
  • D. Vapours only collect near the funnel
Answer: A — Vapours tend to sink and collect in low points such as pump room bilges and under decks
A vapour heavier than air flows along the deck and gathers in low spaces, sumps, pump room bottoms and enclosed spaces. This is why pump room exhausts draw from below floor plates and gas testing must cover the lower levels of a space.

17. Which chemical cargo is fully miscible with water?

  • A. Methanol
  • B. Benzene
  • C. Toluene
  • D. Xylene
Answer: A — Methanol
Methanol mixes completely with water in all proportions, whereas benzene, toluene and xylene are practically insoluble and float. Miscibility affects spill behaviour, choice of fire-fighting medium (alcohol-resistant foam for water-miscible liquids) and tank cleaning method.

18. What does the vapour pressure of a chemical cargo indicate?

  • A. Its tendency to evaporate; the higher the vapour pressure, the more vapour it releases at a given temperature
  • B. Its resistance to flow
  • C. The temperature at which it solidifies
  • D. Its density compared with water
Answer: A — Its tendency to evaporate; the higher the vapour pressure, the more vapour it releases at a given temperature
Vapour pressure is the pressure exerted by the vapour in equilibrium with the liquid at a given temperature. Cargoes with high vapour pressure evaporate readily, producing more vapour that may be toxic or flammable and placing greater demand on venting and vapour return systems.

19. How does the viscosity of most liquid chemical cargoes change when they are heated?

  • A. It decreases, making the cargo easier to pump
  • B. It increases sharply
  • C. It remains unchanged
  • D. It falls to zero above 40°C
Answer: A — It decreases, making the cargo easier to pump
Heating reduces the viscosity of most liquids, which is why viscous cargoes are heated before and during discharge to improve pumping and stripping. Heating must stay within the shipper's instructions and the coating and adjacent-cargo limits.

20. Which hazard grouping on the IBC Code chapter 17 table is shown by the letter 'S' in column d?

  • A. Safety hazard
  • B. Solidifying cargo
  • C. Special area restriction
  • D. Stainless steel tank required
Answer: A — Safety hazard
Column d of IBC Code chapter 17 shows the hazard basis for the product's requirements: S for safety hazards, P for pollution hazards, and S/P for both. This drives whether full safety provisions or mainly pollution provisions apply.

21. Which group of substances includes caustic soda solution and aqueous ammonia?

  • A. Alkalis (bases)
  • B. Mineral acids
  • C. Aromatic hydrocarbons
  • D. Esters
Answer: A — Alkalis (bases)
Caustic soda (sodium hydroxide) solution and aqueous ammonia are alkalis, with a pH above 7. They are corrosive to skin and eyes, react exothermically with acids and attack certain metals such as aluminium, zinc and copper alloys.

22. Which statement about esters such as vinyl acetate and ethyl acetate is correct?

  • A. They are formed from an acid and an alcohol and are generally flammable solvents
  • B. They are inorganic acids
  • C. They are non-flammable inert gases
  • D. They are always solid at ambient temperature
Answer: A — They are formed from an acid and an alcohol and are generally flammable solvents
Esters are organic compounds formed by reacting an acid with an alcohol. Ethyl acetate and vinyl acetate are flammable liquids with low flash points; vinyl acetate monomer can also polymerise and is shipped with an inhibitor.

23. Which property mainly determines whether a cargo spilled in water will float, sink or dissolve?

  • A. Its density and solubility in water
  • B. Its flash point alone
  • C. Its auto-ignition temperature
  • D. Its colour on the Pt-Co scale
Answer: A — Its density and solubility in water
A spilled chemical that is insoluble and lighter than water floats, one that is denser sinks, and a soluble one dissolves. These properties, shown in the SDS and used in GESAMP hazard profiles, determine spill behaviour and response.

24. Phenol, paraffin wax and some fatty acids are carried heated mainly because they have:

  • A. High melting points and solidify at ambient temperature
  • B. Very low flash points
  • C. Very high vapour pressures
  • D. Low densities
Answer: A — High melting points and solidify at ambient temperature
Cargoes with high melting points solidify in the tank and lines if not kept above their melting point. They are carried heated within the shipper's instructions and, under MARPOL Annex II, may be solidifying substances requiring a prewash if unloaded too close to the melting point.

25. Which organisation's hazard evaluation of substances forms the basis for assigning MARPOL Annex II pollution categories?

  • A. GESAMP (Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection)
  • B. OCIMF
  • C. SIGTTO
  • D. Chemical Distribution Institute
Answer: A — GESAMP (Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection)
The GESAMP Evaluation of the Hazards of Harmful Substances Carried by Ships produces hazard profiles covering bioaccumulation, toxicity and effects on human health and amenities. MARPOL Annex II Appendix I uses these profiles to assign categories X, Y and Z.

26. Why should a tank of inhibited styrene monomer not be stowed adjacent to a tank carrying a cargo heated to a high temperature?

  • A. Heat speeds up polymerisation and depletes the inhibitor, which can lead to a runaway reaction
  • B. Heat raises the flash point of styrene above the safe limit
  • C. Heat causes styrene to separate into water and hydrocarbon layers
  • D. Heat makes styrene incompatible with stainless steel
Answer: A — Heat speeds up polymerisation and depletes the inhibitor, which can lead to a runaway reaction
Polymerisation is exothermic and self-accelerating; heat transferred from an adjacent hot cargo increases the reaction rate and consumes the inhibitor faster, so heat-sensitive monomers must be kept away from heated tanks and their temperature monitored.

27. Some inhibitors used in monomer cargoes are oxygen-dependent. What does this mean for the atmosphere in the cargo tank?

  • A. A minimum oxygen level must be kept in the vapour space, so the tank must not be fully inerted
  • B. The tank must be inerted to below 1% oxygen before loading
  • C. The tank must be ventilated continuously with fresh air during the voyage
  • D. The cargo must be padded with carbon dioxide instead of nitrogen
Answer: A — A minimum oxygen level must be kept in the vapour space, so the tank must not be fully inerted
An oxygen-dependent inhibitor needs a small amount of dissolved oxygen to work. The IBC Code (15.13) requires the inhibitor certificate to state the minimum oxygen level needed in the vapour space, so complete inerting could make the inhibitor ineffective.

28. Isocyanates such as TDI and MDI are carried under dry nitrogen mainly because they:

  • A. React with water or moist air, forming solids and carbon dioxide that can pressurise the tank
  • B. Are pyrophoric and ignite spontaneously in air
  • C. Polymerise only when exposed to nitrogen-free atmospheres
  • D. Have a flash point below ambient temperature
Answer: A — React with water or moist air, forming solids and carbon dioxide that can pressurise the tank
Isocyanates react with water, including moisture in air, producing insoluble ureas and carbon dioxide gas. This contaminates the cargo and can build pressure in a closed tank, so tanks and lines must be perfectly dry and the cargo kept under dry nitrogen padding.

29. Which pair of cargoes would be shown as incompatible on a cargo compatibility chart and must not be stowed in adjacent tanks without proper segregation?

  • A. Sulphuric acid and caustic soda solution
  • B. Toluene and xylene
  • C. Methanol and ethanol
  • D. Palm oil and soybean oil
Answer: A — Sulphuric acid and caustic soda solution
A strong mineral acid and a strong alkali react violently with the release of a great deal of heat. Compatibility charts such as the USCG chart (46 CFR Part 150) mark such reactive group combinations as unsafe, requiring segregation by cofferdam or other approved separation.

30. Why must acrylic acid be prevented from freezing during the voyage?

  • A. When it freezes, the inhibitor separates from the crystals and the thawed liquid may be uninhibited and polymerise
  • B. Frozen acrylic acid expands and ruptures stainless steel tanks
  • C. Freezing converts acrylic acid into a toxic gas
  • D. Frozen acrylic acid cannot be tested for inhibitor content
Answer: A — When it freezes, the inhibitor separates from the crystals and the thawed liquid may be uninhibited and polymerise
Acrylic acid freezes at about 13°C. On freezing the inhibitor concentrates in the remaining liquid, leaving crystals with little protection; careless or local overheating during thawing can then start violent polymerisation, so temperature is kept within the shipper's range.

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