Hydrogen Sulfide
Hydrogen sulfide is a highly toxic, flammable, colorless gas that is heavier than air. It is produced naturally by decaying organic matter and is also a by-product of many industrial processes. Hazardous levels may be found in petroleum refineries, tanneries, mines, pulp-making factories, sulfur hot springs, carbon disulfide production, commercial fishing holds, hot asphalt fumes, and pools of sewage sludge or liquid manure. It sometimes is referred to as “pit gas.” There have been reports of suicide by mixing acid-containing household cleaners with calcium sulfide–containing bath salts to generate hydrogen sulfide gas.
Mechanism of toxicity. Hydrogen sulfide causes cellular asphyxia by inhibition of the cytochrome oxidase system, similar to the action of cyanide. Because it is absorbed rapidly by inhalation, symptoms occur nearly immediately after exposure, leading to rapid unconsciousness, or “knockdown.” Hydrogen sulfide is also a mucous membrane irritant.
Toxic dose. The characteristic rotten egg odor of hydrogen sulfide is detectable at concentrations as low as 0.025 ppm. The recommended workplace limit (ACGIH TLV-TWA) is 10 ppm (14 mg/m3) as an 8-hour time-weighted average, with a short-term exposure limit (STEL) of 15 ppm (21 mg/m3
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