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 cargo requires pumping to a dedicated slop tank only

Answer

Professional supervision by a Marine Chemist is mandatory during cleaning

Answer

Pressure testing of the tank is required after cleaning

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

16.0% by volume

Answer

18.0% by volume

Answer

21.0% by volume

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

The machines must be painted high-visibility orange for identification

Answer

The machines must be operated only when the vessel is at anchor and not underway

Answer

The machines must be connected directly to the ship's fixed inert gas system

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

Crew members retained on board during hazardous cargo cleaning operations

Answer

Cargo legally held on board pending resolution of a commercial dispute

Answer

Bunker fuel retained on board that is exempt from pollution regulations

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

LEL reading below 50% of the lower explosive limit

Answer

LEL reading below 10% of the lower explosive limit

Answer

No flammability testing is required if the tank has been fully water washed and drained

Question 6

What is the purpose of 'gas-freeing' a cargo tank after the cleaning process is complete?

Accepted Answer

To replace hazardous vapors remaining after washing with fresh air until the space is safe for entry and hot work

Answer

To remove wash water from the tank by evaporation before the next cargo

Answer

To fill the cleaned tank with inert gas to protect the coating before the next cargo

Answer

To pressurize the tank with compressed air to test for leaks in the tank structure

Question 7

Under NFPA 306, what is the Marine Chemist's obligation regarding cargo residues that could re-contaminate a tank atmosphere after initial safe readings are obtained?

Accepted Answer

The Marine Chemist must evaluate whether residues could off-gas and render the atmosphere unsafe after certification

Answer

The Marine Chemist has no obligation once safe initial readings are documented

Answer

The Marine Chemist must physically remove all visible residues before issuing any certificate

Answer

The Marine Chemist must only document residues exceeding 5% of the tank volume