CHEMCO exit exam questions and answers — Set 9 — Advanced Training for Chemical Tanker Cargo Operations
Set 9 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 9 — 30 CHEMCO exit exam questions with answers
1. A diffuse discharge from a single sharp conductor is called
- A. A spark
- B. A corona
- C. A brush discharge
- D. A Propagating brush discharge
Answer: B — A corona
A corona is a diffuse, low-energy discharge from a single sharp conductor where the electric field is concentrated. ISGOTT notes it is usually less incendive than a spark or brush discharge, which jump between surfaces or come from rounded objects.
2. What is the type of gas detection system fitted for spaces with air?
- A. Spot metering type fixed inside the individual insulation spaces
- B. Infrared type using sequential measurement
- C. Portable gas detection system due to mobility of this method
- D. Catalytic combustion type
Answer: D — Catalytic combustion type
Spaces that normally contain air are monitored with catalytic combustion (pellistor) sensors, which burn the gas on a heated catalytic element. This needs the oxygen in air, so infrared or thermal conductivity instruments are used for inerted or oxygen-deficient spaces instead.
3. Class B fires involve
- A. Solid cellulosic materials such as wood, paper, clothing, etc.
- B. Vapour/air mixture over the surface of flammable liquids
- C. Energised electrical equipment
- D. Combustible materials such as magnesium, sodium, etc.
Answer: B — Vapour/air mixture over the surface of flammable liquids
Class B fires involve flammable liquids, where it is actually the vapour/air mixture above the liquid surface that burns. They are fought with foam, dry powder or CO2 to smother the surface, while water jets can spread the burning liquid.
4. Lower flammable limit (LFL) or Lower Explosive Limit (LEL), is usually expressed:
- A. as a percentage of the air volume
- B. as a percentage of hydrocarbon volume
- C. in volume percent
- D. as a percentage of the volume of oxygen
Answer: C — in volume percent
The lower flammable limit is the minimum concentration of a gas or vapour in air that can be ignited. It is expressed as a percentage by volume of the gas in the mixture, for example about 1% by volume for typical petroleum gases.
5. For Oxygen analyzer, identify the statement that explains the working principle
- A. Electrochemical Sensors: Analyzers of this type determine the oxygen content of a gas mixture by measuring the output of an electrochemical cell.
- B. Oxygen diffuses through a membrane into the cell and current flows between two special electrodes separated by a liquid or gel electrolyte.
- C. The current flow is related to the oxygen concentration in the sample and the scale is arranged to give a direct indication of oxygen content.
- D. The analyzer readings are directly proportional to the pressure in the measuring cell, and only small errors are caused by normal variations in atmospheric pressure.
Answer: B — Oxygen diffuses through a membrane into the cell and current flows between two special electrodes separated by a liquid or gel electrolyte.
In an electrochemical oxygen analyser, oxygen diffuses through a membrane into a cell where current flows between two electrodes separated by a liquid or gel electrolyte. The current produced is proportional to the oxygen concentration, which is then displayed directly.
6. The bypass valve on a self-contained breathing apparatus (SCBA) bypasses
- A. a breathing bag containing excessive pressure
- B. the regulator in an emergency
- C. oxygen to the atmosphere
- D. the regenerator in an emergency
Answer: B — the regulator in an emergency
The bypass valve on an SCBA lets air flow from the cylinder directly to the face mask without passing through the demand regulator. It is used in an emergency if the regulator fails or the wearer needs extra air, though it uses up the cylinder supply quickly.
7. A fuel tank is considered to be gas free when the tank is
- A. free of most flammable gas concentrations
- B. thoroughly ventilated for at least 24 hours
- C. inerted with carbon dioxide for 24 hours
- D. free of all dangerous concentrations of flammable or toxic gases
Answer: D — free of all dangerous concentrations of flammable or toxic gases
A tank is gas free when enough fresh air has been introduced to lower all flammable, toxic and inert gas levels to the required safe limits, as confirmed by testing. ISGOTT stresses that gas free status depends on measurements, not on time spent ventilating.
8. Which of the gases listed is the poisonous gas most likely to be found in a closed compartment involved in a fire?
- A. Nitrogen
- B. Hydrogen
- C. Carbon dioxide
- D. Carbon monoxide
Answer: D — Carbon monoxide
A fire in a closed compartment soon runs short of oxygen, so combustion is incomplete and carbon monoxide is produced. CO is highly toxic because it binds to haemoglobin much more readily than oxygen, and it has no smell or colour.
9. Which type of cargoes are often known as static accumulator cargoes?
- A. Crude oil
- B. Vegetable oil
- C. Highly refined petroleum products
- D. Animal oil
Answer: C — Highly refined petroleum products
Highly refined products such as gas oil, kerosene and jet fuel have very low electrical conductivity, so electrostatic charge relaxes slowly. ISGOTT calls them static accumulators, and they require reduced initial loading rates and precautions with dipping.
10. What is the priority order of a Company's on board policies and procedures?
- A. Safety of the crew; Safe operation of the vessel; Protection of the environment
- B. Safe operation of the vessel; Safety of the crew; Protection of the environment
- C. Protection of the environment; Safety of the crew; Safe operation of the vessel
- D. Protection of the environment; Safe operation of the vessel; Safety of the crew
Answer: A — Safety of the crew; Safe operation of the vessel; Protection of the environment
Company procedures under the ISM Code rank safety of life first, then safe operation of the vessel, then protection of the environment. Human life always comes first, and a safely operated ship is the best protection against pollution.
11. When preparing to pump flammable liquids with a centrifugal pump, you should
- A. draw a small quantity of liquid to prime the pump
- B. check for gland leakage and any fire hazard
- C. have a standby pump running with the discharge valve closed
- D. lift the relief valve by hand to check its operation
Answer: B — check for gland leakage and any fire hazard
Before pumping flammable liquids, the pump glands and seals should be checked for leakage and the surrounding area for any fire hazard. A leaking gland can release flammable liquid or vapour into the pump room close to hot surfaces or electrical equipment.
12. Certain operations can give rise to accumulations of electric charge which may be released suddenly in electrostatic discharges with sufficient energy to ignite
- A. Flammable hydrocarbon gas/air mixtures
- B. Flammable hydrocarbon gas/Nitrogen mixtures
- C. Combustible hydrocarbon liquid
- D. Flammable hydrocarbon gas/CO2 mixtures
Answer: A — Flammable hydrocarbon gas/air mixtures
Electrostatic discharges can ignite flammable hydrocarbon gas/air mixtures because air supplies the oxygen needed for combustion. Mixtures with nitrogen or CO2 lack enough oxygen to burn, which is the principle behind inerting cargo tanks.
13. How many portable multi – gas detectors should be carried onboard?
- A. At least one with methane gas and one of propane gas detection capability
- B. At least one with methane and one of carbon monoxides gas detection capability
- C. At least one with methane gas and one of ammonia gas detection capability
- D. At least two sets with methane gas detection capability
Answer: D — At least two sets with methane gas detection capability
Gas-fuelled and gas carrier ships use methane-type flammable gas detection, and the requirement is for at least two portable gas detectors with methane detection capability. Having two sets allows one to be used while the other is calibrated or repaired.
14. Class A fires involve
- A. Solid cellulosic materials such as wood, paper, clothing, etc.
- B. Vapour/air mixture over the surface of flammable liquids
- C. Energised electrical equipment
- D. Combustible materials such as magnesium, sodium, etc.
Answer: A — Solid cellulosic materials such as wood, paper, clothing, etc.
Class A fires involve ordinary solid combustible materials such as wood, paper, cloth and rubbish, which leave embers. They are best extinguished with water, which cools the fuel below its ignition temperature.
15. The ISM Code requires work procedures which ensures ________ performance
- A. Superior
- B. Profitable
- C. Safe
- D. Excellent
Answer: C — Safe
The ISM Code requires the company to establish procedures and instructions so that key shipboard operations are performed safely and in an environmentally sound way. Its aim is safe operation and prevention of injury, loss of life and pollution, not profit or excellence.
16. What is the procedure for checking for spinal cord damage in an unconscious patient?
- A. Beginning at the back of the neck, and proceeding to the buttocks, press the spine to find where it hurts
- B. Prick the skin of the hands and the soles of the feet with a sharp object to check for reaction
- C. Selectively raise each arm and each leg and watch patient's face to see if he registers pain
- D. Roll patient onto his stomach and prick along the length of his spine to check reaction
Answer: B — Prick the skin of the hands and the soles of the feet with a sharp object to check for reaction
In an unconscious casualty, spinal cord damage is checked by lightly pricking the skin of the hands and the soles of the feet and watching for a reflex response. No response suggests nerve damage, and the casualty must not be moved unnecessarily or rolled about.
17. The airborne concentrations of substances (such as hydrogen sulfide) under which nearly all workers may be repeatedly exposed without adverse effects are called
- A. exposure limits
- B. concentration limits
- C. threshold limit values
- D. substance limit values
Answer: C — threshold limit values
Threshold limit values are airborne concentrations of a substance to which nearly all workers may be exposed repeatedly, day after day, without adverse effects. ISGOTT and the Tanker Safety Guide express them as TWA, STEL and ceiling values.
18. Optimum Oxygen values in the inert gas for delivery into cargo tanks is between:
- A. 1 to 2%
- B. 3 to 4%
- C. 5 to 6%
- D. 9 to 10%
Answer: B — 3 to 4%
The FSS Code requires inert gas with oxygen content of 5% or less by volume to cargo tanks. A well-run flue gas system normally delivers around 3 to 4% oxygen, keeping a margin below the 8% maximum allowed in the tanks.
19. If a cargo tank has not been certified as gas free,
- A. breathing apparatus would not be necessary in an emergency as you would only be in the tank a short time
- B. a man may work safely without breathing apparatus in cold weather, as vapors are less volatile
- C. entry without a breathing apparatus may be made at the top of the tank since petroleum vapors are heavier than air
- D. breathing apparatus should always be used
Answer: D — breathing apparatus should always be used
If a cargo tank has not been certified gas free, its atmosphere may contain hydrocarbon, toxic gas or too little oxygen. Entry must not be made without breathing apparatus, even briefly or in cold weather, as dangerous concentrations may be present anywhere in the tank.
20. Cargo tank pressure is monitored on tankers:
- A. To ensure IG backpressure is slightly positive at all times
- B. To prevent back pressure
- C. To ensure enough tanks are open for loading
- D. To ensure that the loading rate is not too high
Answer: A — To ensure IG backpressure is slightly positive at all times
Cargo tank pressure is monitored to make sure inert gas pressure stays slightly positive at all times. Positive pressure stops air entering and keeps oxygen below 8%, while staying within the P/V valve and breaker settings.
21. Identify the statement that highlights the purpose of using a non-catalytic heated filament gas indicator,
- A. The working of catalytic gas indicator depends on the property of its combustion with air.
- B. Since the inerted atmosphere is deficient in oxygen the catalytic gas indicators cannot be used in inerted atmospheres.
- C. Instruments used in inerted atmosphere have a filament sensitive to the variations in the heat conductivity.
- D. Instruments used in inerted atmosphere have a filament that are good for monitoring inerting operations.
Answer: B — Since the inerted atmosphere is deficient in oxygen the catalytic gas indicators cannot be used in inerted atmospheres.
Catalytic gas indicators work by burning gas on a heated element, which needs the oxygen in air. Because inert atmospheres lack enough oxygen, catalytic instruments give false low readings, so non-catalytic heated filament or infrared instruments are used instead.
22. The highest concentration of a harmful substance to which a person may be exposed without danger to health, is termed the
- A. vapor pressure
- B. tolerance point
- C. threshold limit value
- D. odor threshold
Answer: C — threshold limit value
The threshold limit value is the highest airborne concentration of a harmful substance to which a person may be repeatedly exposed without danger to health. It is not the same as the odour threshold, as many dangerous gases cannot be smelled at harmful levels.
23. Vessel's enclosed spaces that are not to be treated as such:
- A. Spaces which must be entered through small hatchways or access points;
- B. Cargo tanks and holds ;
- C. Double-bottom tanks;
- D. Crew accommodation
Answer: D — Crew accommodation
IMO Resolution A.1050(27) lists cargo holds and tanks, double bottoms and spaces entered through small hatches as enclosed spaces. Crew accommodation is ventilated and normally occupied, so it is not treated as an enclosed space.
24. Which would be the appropriate arrangement for entering into a DB tank through the ductkeel?
- A. Entry permit for ductkeel and standby person at the entrance
- B. Entry permit for DB tank and standby person loacated inside ductkeel outside DB tank
- C. Combined entry permit for both but standby person ductkeel entrance and DB entrance
- D. Separate enclosed space entry permit for both spaces including standby person outside both
Answer: D — Separate enclosed space entry permit for both spaces including standby person outside both
The duct keel and the double-bottom tank are separate enclosed spaces with different atmospheres, so each needs its own entry permit and atmosphere testing. A standby person must be stationed outside each space, as required by IMO A.1050(27).
25. Which of the devices listed would be safe to use in a compartment with insufficient oxygen?
- A. Wet handkerchief.
- B. Self-contained breathing apparatus.
- C. Dust or gas mask.
- D. Canister type mask.
Answer: B — Self-contained breathing apparatus.
Only a self-contained breathing apparatus supplies its own air, so it is the only device safe to use where oxygen is too low. Canister, dust and gas masks merely filter the surrounding air and give no protection against oxygen deficiency.
26. Where is the electrostatic discharge plate installed?
- A. Near the cargo manifold
- B. At the forward end of the ship
- C. At the accommodation entrance on upper deck
- D. At the aft part of the ship
Answer: C — At the accommodation entrance on upper deck
An electrostatic discharge plate is fitted at the accommodation entrance on the upper deck so that personnel can discharge any static charge on their bodies by touching it before going onto the cargo deck. This stops a person becoming a spark source near flammable vapour.
27. For Oxygen analyzer, identify the key principle upon which the analyzer is working,
- A. A Wheatstone bridge circuit is formed using the two wires. It is used to measure a resistance by balancing two legs of the circuit.
- B. The sample of atmosphere is filtered and passed through a diffuser before reaching the two chambers.
- C. One chamber is with a magnetic field and the other without a magnetic field.
- D. A difference in the thermal conductivity of the oxygen with respect to air is developed and this causes an imbalance in the resistance.
Answer: D — A difference in the thermal conductivity of the oxygen with respect to air is developed and this causes an imbalance in the resistance.
A paramagnetic (magnetic wind) oxygen analyser uses a heated filament in a magnetic field. Oxygen is attracted into the field, then heated and pushed out, and this changes the thermal conductivity around the filament compared with the reference. The resulting resistance imbalance indicates oxygen content.
28. The ________ depends upon the pressure of contact exerted on live wires.
- A. voltage
- B. current
- C. impedance
- D. power
Answer: C — impedance
Contact pressure on live wires determines contact resistance, which forms part of the circuit impedance. A loose or poor connection has high impedance at the joint, which causes heating and arcing, a common cause of electrical fires.
29. What is related to the relaxation time of the material in which the electical charges are accumulated?
- A. That material's density
- B. That material's viscosity
- C. That material's conductivity
- D. That material's flammabilty
Answer: C — That material's conductivity
Relaxation time is the time taken for an accumulated electrostatic charge to dissipate, and it depends on the electrical conductivity of the material. Low-conductivity liquids such as refined products have long relaxation times, which is why ISGOTT treats them as static accumulators.
30. Operating Principle of the Infrared instrument: identify the key principle that leads to detection of hydrocarbon gas,
- A. The amount of absorption is related to the concentration of the gas and is measured by a set of optical detectors and suitable electronic systems.
- B. The change in the intensity of the absorbed light is measured relative to the intensity of light at a non-absorbed wavelength.
- C. When there is no gas present the signals of reference signal detector and measurement signal detector are balanced.
- D. When there is combustible gas present, there is a predictable drop in the output from measurement signal detector because the gas is absorbing light.
Answer: D — When there is combustible gas present, there is a predictable drop in the output from measurement signal detector because the gas is absorbing light.
An infrared gas detector compares a measurement signal at a wavelength that hydrocarbons absorb with a reference signal at a non-absorbed wavelength. When hydrocarbon gas is present, light is absorbed and the measurement signal drops predictably, and this imbalance indicates the gas concentration.
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