Tanker Familiarization Tank Atmosphere Control 2 — Questions and Answers
Question 1: What is the primary purpose of an inert gas system on a tanker?
- To cool the cargo during transport
- To replace oxygen in the cargo tank with a non-flammable gas (Correct answer)
- To increase the pressure inside cargo tanks
- To remove water vapor from the cargo tanks
Correct answer: To replace oxygen in the cargo tank with a non-flammable gas
An inert gas system replaces oxygen in cargo tanks with a non-flammable gas (typically flue gas or nitrogen) to prevent flammable atmospheres.
Question 2: Which of the following oxygen concentrations is considered safe for inerted cargo tanks?
- Less than 21% by volume
- Less than 8% by volume (Correct answer)
- Less than 15% by volume
- Less than 12% by volume
Correct answer: Less than 8% by volume
Cargo tanks must be maintained at less than 8% oxygen by volume to ensure the atmosphere remains outside the flammable range.
Question 3: What is the 'Lower Explosive Limit' (LEL) in the context of tank atmosphere control?
- The minimum temperature at which cargo ignites
- The minimum concentration of vapor in air at which ignition can occur (Correct answer)
- The lowest pressure at which a tank can safely operate
- The minimum oxygen level required for combustion
Correct answer: The minimum concentration of vapor in air at which ignition can occur
The LEL is the minimum concentration of flammable vapor in air below which a flame will not propagate.
Question 4: When must a tanker maintain a positive pressure in inerted cargo tanks?
- Only during cargo discharge
- At all times while inerted, including during sea passage (Correct answer)
- Only when connected to shore terminal
- Only during loading operations
Correct answer: At all times while inerted, including during sea passage
Positive pressure must be maintained at all times in inerted tanks to prevent air ingress, which could create a flammable atmosphere.
Question 5: What instrument is used to measure the oxygen content inside a cargo tank?
- Explosimeter
- Oxygen analyzer (Correct answer)
- Manometer
- Hydrometer
Correct answer: Oxygen analyzer
An oxygen analyzer measures the percentage of oxygen by volume in the tank atmosphere to verify safe inerted conditions.
Question 6: Which condition describes a 'gas-free' tank atmosphere?
- A tank containing no inert gas
- A tank where hydrocarbon vapor is below 1% LEL and oxygen is at normal atmospheric levels (Correct answer)
- A tank at atmospheric pressure with no cargo residue
- A tank that has been washed with water
Correct answer: A tank where hydrocarbon vapor is below 1% LEL and oxygen is at normal atmospheric levels
A gas-free atmosphere contains negligible hydrocarbon vapors (less than 1% LEL) and normal oxygen levels, making it safe for personnel entry.
Question 7: What happens to flammable cargo vapors in the 'Upper Explosive Limit' (UEL) zone?
- The mixture is too lean to ignite
- The mixture is too rich in fuel to ignite (Correct answer)
- The mixture burns with maximum intensity
- The mixture condenses back to liquid form
Correct answer: The mixture is too rich in fuel to ignite
Above the UEL, there is too much fuel and not enough oxygen, so the mixture cannot ignite under normal conditions.
Tanker Familiarization Tank Atmosphere Control 2
What is the primary purpose of an inert gas system on a tanker?