Deck General · Enclosed Space
A normal, safe oxygen content for entering an enclosed space is approximately:
- A10% by volume
- B16% by volume
- C20.9% by volume✓ Correct
- D30% by volume
Explanation
Normal air is about 20.9% oxygen. Levels below roughly 19.5% are oxygen-deficient and unsafe; enriched atmospheres above ~23.5% increase fire risk. Entry requires a reading near 20.9% along with safe gas readings.
Authority: IMO Res. A.1050(27); OSHA confined space standards
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