SafetyQuestion 692 of 700
In a permit-required confined space, normal air is about 20.9 percent oxygen. Which oxygen readings define an atmosphere that is unsafe to enter without correction?
a.Between 20 and 21 percent
b.Exactly 20.9 percent only
c.Anything above 18 percent is always safe
d.Oxygen-deficient below about 19.5 percent, or oxygen-enriched above about 23.5 percent
Explanation
Correct: an atmosphere is oxygen-deficient below about 19.5 percent (risk of impairment and asphyxiation) and oxygen-enriched above about 23.5 percent (greatly increased fire/combustion risk); both are hazardous. A 20 to 21 percent band and exactly 20.9 percent are normal but far too narrow as safety limits. 'Anything above 18 percent is safe' is wrong because 18 to 19.5 percent is already deficient and enrichment is also dangerous.
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