Tankerman · Safety — Inert Gas
An inert gas system keeps a cargo tank atmosphere safe by holding oxygen content below approximately:
- A21 percent by volume
- B8 percent by volume✓ Correct
- C15 percent by volume
- D2 percent by volume
Explanation
A properly inerted tank is maintained at 8 percent oxygen by volume or less, well below the roughly 11 percent needed to support combustion of hydrocarbon vapor. This prevents the atmosphere from ever entering the flammable range.
Authority: Tank Vessel Operations — Inert Gas (SOLAS II-2)
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