Tankerman · Safety — Flammability
A hydrocarbon vapor/air mixture will burn only when its concentration is:
- ABelow the lower flammable limit
- BBetween the lower and upper flammable limits✓ Correct
- CAbove the upper flammable limit
- DAt exactly 21 percent oxygen
Explanation
Combustion is possible only within the flammable range — between the lower flammable limit (too lean below) and the upper flammable limit (too rich above). Inerting keeps the mixture too lean in oxygen to burn at all.
Authority: Tank Vessel Safety (USCG topic)
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