CMC Cargo Tank Cleaning Procedures & Residue Management

Question 1

What is the primary purpose of prewashing a cargo tank before gas-freeing operations on a chemical tanker?

Accepted Answer

To remove cargo residues that could produce flammable or toxic vapors during gas-freeing

Answer

Prewashing removes cargo residues that would otherwise continue to off-gas hazardous vapors during gas-freeing, making the process safer and more effective.

Question 2

According to MARPOL Annex II, which types of chemical tanker cargoes require mandatory prewashing before washings may be discharged to the sea?

Accepted Answer

High-viscosity substances and solidifying substances that cannot be effectively stripped

Answer

MARPOL Annex II mandates prewashing for high-viscosity and solidifying substances because residues cling to tank surfaces and cannot be removed by pumping alone.

Question 3

When a cargo tank has carried a Category X substance under MARPOL Annex II, what must occur before the vessel may proceed to sea?

Accepted Answer

The tank must be prewashed and the washings discharged to a shore reception facility

Answer

Category X substances are most harmful to the marine environment; MARPOL requires prewashing and discharge of washings to a reception facility before the vessel departs.

Question 4

What is 'clingage' in the context of cargo tank cleaning operations?

Accepted Answer

Cargo residue that adheres to tank surfaces and cannot be removed by pumping alone

Answer

Clingage is cargo residue that sticks to tank surfaces after pumping is complete; it must be removed by washing before the tank atmosphere can be made safe.

Question 5

Which type of tank cleaning method is most appropriate when switching between cargoes that are incompatible with water?

Accepted Answer

Solvent washing or dry cleaning methods compatible with both cargoes

Answer

When cargoes are incompatible with water or the next cargo cannot tolerate water contamination, solvent washing or dry cleaning methods must be used to avoid product damage or dangerous reactions.

(CMC) Certified Marine Chemist Practice Test

(CMC) Certified Marine Chemist Practice Test

CMC Cargo Tank Cleaning Procedures & Residue Management