Cargo Tank Cleaning Procedures & Residue Management Flashcards
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In the IBC Code tank cleaning column, what does the notation 'P' indicate for a listed cargo?
Answer: Prewashing of the cargo tank is required before gas-freeing operations
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.
What is the minimum oxygen concentration by volume required in a cargo tank atmosphere before personnel may enter for cleaning or inspection?
Answer: 19.5% by volume
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.
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?
Answer: The machines must be certified intrinsically safe or explosion-proof to prevent ignition
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.
What does 'Retention on Board' (ROB) refer to in the context of cargo tank cleaning and Marine Chemist certification?
Answer: Cargo residue remaining in the tank after discharge that must be documented under MARPOL
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.
When issuing a hot work certificate for a tank that previously contained a flammable liquid, what flammability reading must the Marine Chemist confirm?
Answer: LEL reading at or near 0% of the lower explosive limit (typically below 1%)
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.
What is the purpose of 'gas-freeing' a cargo tank after the cleaning process is complete?
Answer: To replace hazardous vapors remaining after washing with fresh air until the space is safe for entry and hot work
Gas-freeing uses mechanical ventilation to displace remaining hazardous vapors with fresh air until all three atmospheric parameters—oxygen, LEL, and toxic gases—are within safe limits.
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?
Answer: The Marine Chemist must evaluate whether residues could off-gas and render the atmosphere unsafe after certification
NFPA 306 requires the Marine Chemist to holistically evaluate conditions, including whether residual cargo could off-gas over time and re-create hazardous atmospheric conditions after safe readings are initially recorded.