Tankerman · Gas Hazards — H2S
Hydrogen sulfide (H2S) is especially dangerous because, at higher concentrations, it:
- ASmells strongly so it is easily detected
- BIs non-toxic below 1000 ppm
- CIs lighter than air and disperses quickly
- DRapidly deadens the sense of smell, removing the warning odor✓ Correct
Explanation
H2S has a rotten-egg odor at low levels but quickly paralyzes the sense of smell, so the warning disappears at dangerous concentrations. It is heavier than air and rapidly lethal; detection relies on instruments.
Authority: ISGOTT (toxic hazards); OSHA H2S guidance
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