FREE Tanker Familiarization Tank Atmosphere Control Questions and Answers

Question 1

According to SOLAS regulations, what is the maximum permissible oxygen content by volume for a cargo tank's atmosphere to be considered effectively inerted?

Accepted Answer

8%

Answer

SOLAS Chapter II-2 requires that inert gas systems maintain the atmosphere in any cargo tank at an oxygen content not exceeding 8% by volume. This provides a crucial safety margin, as most hydrocarbon vapors cannot burn in an atmosphere with less than approximately 11% oxygen.

Question 2

A tanker is discharging cargo when the Inert Gas (IG) system fails, causing the pressure in the tanks to drop. What is the most critical and immediate hazard created by this situation?

Accepted Answer

Air being drawn into the tank, potentially creating a flammable atmosphere.

Answer

When the IG system fails during discharge, the removal of liquid creates a vacuum. If this is not compensated for by inert gas, air will be drawn into the tank from the atmosphere. This introduction of air (oxygen) can raise the oxygen level above 8%, potentially bringing the tank atmosphere into the flammable range, which creates a severe risk of explosion.

Question 3

Which of the following correctly describes the primary purpose of 'purging' a cargo tank with inert gas immediately after cargo discharge and before commencing gas-freeing?

Accepted Answer

To reduce the hydrocarbon vapor concentration to a level below 2% by volume before introducing air.

Answer

Purging with inert gas is a critical intermediate step. Its purpose is to displace or dilute the hydrocarbon vapors, reducing their concentration to a safe level (typically below 2% by volume) so that when fresh air is subsequently introduced for gas-freeing, the tank's atmosphere never passes through the flammable range.

Question 4

When preparing a tank for man-entry, what is the primary objective of the 'gas-freeing' operation that follows purging?

Accepted Answer

To displace the inert gas with fresh air, raising the oxygen level to 21% and ensuring hydrocarbon levels are safe.

Answer

After purging has reduced hydrocarbon levels, gas-freeing is the final step to make a tank safe for human entry. This process involves ventilating the tank with fresh air to displace the oxygen-deficient inert gas, with the goal of achieving a stable 21% oxygen level and ensuring any remaining toxic or flammable vapors are below safe occupational exposure limits.

Question 5

A tanker is loading at a terminal equipped with a Vapor Emission Control System (VECS). A high-pressure alarm for the cargo tanks sounds. Which of the following is the most probable cause related to the VECS operation?

Accepted Answer

A blockage or closed valve exists in the vapor return line to the shore facility.

Answer

A VECS is designed to safely transfer vapors from the ship's tanks back to the shore facility to prevent their release into the atmosphere. If the vapor return line is blocked, or a valve is mistakenly closed, the vapors displaced by the incoming cargo cannot escape, causing a rapid and dangerous build-up of pressure in the tank, which would trigger the high-pressure alarm.

Tanker Familiarization Practice Test

Tanker Familiarization Practice Test

FREE Tanker Familiarization Tank Atmosphere Control Questions and Answers