Tanker Familiarization Inert Gas Systems 1 — Questions and Answers
Question 1: What is the primary purpose of an inert gas system (IGS) on a tanker?
- To cool cargo tanks during transit
- To prevent explosive atmospheres in cargo tanks (Correct answer)
- To increase cargo loading and discharge speed
- To clean cargo tank residues after discharge
Correct answer: To prevent explosive atmospheres in cargo tanks
The IGS displaces oxygen in cargo tanks with inert gas, preventing the formation of explosive hydrocarbon-air mixtures.
Question 2: What is the maximum allowable oxygen content by volume in a cargo tank that is considered properly 'inerted'?
- 8% (Correct answer)
- 15%
- 21%
- 12%
Correct answer: 8%
A tank atmosphere with oxygen content below 8% by volume is considered inerted and incapable of supporting combustion of hydrocarbon vapors.
Question 3: Which component of the inert gas system prevents cargo vapors from flowing back into the engine room?
- Pressure/vacuum (P/V) valve
- Oxygen analyzer
- Deck water seal (Correct answer)
- Scrubber tower
Correct answer: Deck water seal
The deck water seal acts as a non-return device, preventing the backflow of flammable cargo vapors through the inert gas main toward the engine room.
Question 4: What is the most common source of inert gas on a crude oil tanker?
- Nitrogen cylinders stored in the pump room
- Flue gas from the ship's boiler or main engine exhaust (Correct answer)
- Carbon dioxide released from the fire suppression system
- Compressed air from the engine room compressors
Correct answer: Flue gas from the ship's boiler or main engine exhaust
Most crude oil tankers use flue gas from the ship's boiler or main engine exhaust as the primary source of inert gas, as it is already low in oxygen from combustion.
Question 5: What process describes reducing the oxygen content in a cargo tank to below 8% using inert gas?
- Purging
- Gas-freeing
- Inerting (Correct answer)
- Ventilating
Correct answer: Inerting
Inerting is the specific process of introducing inert gas into a cargo tank to reduce the oxygen content to below 8% by volume, rendering the atmosphere unable to support ignition.
Question 6: According to SOLAS, inert gas systems are required on tankers with a minimum deadweight tonnage (DWT) of:
- 10,000 DWT
- 20,000 DWT (Correct answer)
- 50,000 DWT
- 5,000 DWT
Correct answer: 20,000 DWT
SOLAS regulations require inert gas systems on tankers of 20,000 DWT and above to protect against explosive tank atmospheres during cargo operations.
Question 7: What instrument is used to continuously monitor the oxygen content in the inert gas being supplied to cargo tanks?
- Hydrocarbon vapor detector
- Carbon monoxide meter
- Oxygen analyzer (Correct answer)
- Combustible gas indicator (CGI)
Correct answer: Oxygen analyzer
An oxygen analyzer continuously measures the percentage of oxygen in the inert gas supply to confirm it remains below 8% before entering the cargo tanks.
Tanker Familiarization Inert Gas Systems 1
What is the primary purpose of an inert gas system (IGS) on a tanker?