CMC Cargo Tank Cleaning Procedures & Residue Management 3

Question 1

In the IBC Code tank cleaning column, what does the notation 'P' indicate for a listed cargo?

Accepted Answer

Prewashing of the cargo tank is required before gas-freeing operations

Answer

The 'P' notation in the IBC Code tank cleaning column indicates that prewashing is required before the tank may be gas-freed, due to the cargo's environmental or safety characteristics.

Question 2

What is the minimum oxygen concentration by volume required in a cargo tank atmosphere before personnel may enter for cleaning or inspection?

Accepted Answer

19.5% by volume

Answer

OSHA and NFPA standards establish 19.5% oxygen by volume as the minimum acceptable level for personnel entry into a confined space including cargo tanks.

Question 3

When portable rotating tank cleaning machines (Butterworth machines) are used in a cargo tank that may contain flammable vapors, what is the essential equipment requirement?

Accepted Answer

The machines must be certified intrinsically safe or explosion-proof to prevent ignition

Answer

Tank cleaning machines used where flammable vapors may be present must be intrinsically safe or explosion-proof to eliminate the risk of electrical sparks igniting the atmosphere.

Question 4

What does 'Retention on Board' (ROB) refer to in the context of cargo tank cleaning and Marine Chemist certification?

Accepted Answer

Cargo residue remaining in the tank after discharge that must be documented under MARPOL

Answer

ROB describes the cargo residue remaining after cargo discharge; it must be documented in the Cargo Record Book under MARPOL and is part of the conditions the Marine Chemist evaluates before certifying the tank.

Question 5

When issuing a hot work certificate for a tank that previously contained a flammable liquid, what flammability reading must the Marine Chemist confirm?

Accepted Answer

LEL reading at or near 0% of the lower explosive limit (typically below 1%)

Answer

NFPA 306 requires the tank atmosphere to be at or near 0% LEL—typically confirmed as below 1%—before hot work is authorized, providing a conservative safety margin.

(CMC) Certified Marine Chemist Practice Test

(CMC) Certified Marine Chemist Practice Test

CMC Cargo Tank Cleaning Procedures & Residue Management 3