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Hydrogen sulfide (H2S) is a colorless, flammable, extremely hazardous gas with a “rotten egg” smell. It occurs naturally in crude petroleum and natural gas, and can be produced by the breakdown of organic matter and human/ animal wastes (e.g., sewage). It is heavier than air and can collect in low-lying and enclosed, poorly ventilated areas such as basements, manholes, sewer lines and underground telephone/electrical vaults.
Health effects
Health effects vary with how long, and at what level, you are exposed. Asthmatics may be at greater risk.
- Low concentrations – irritation of eyes, nose, throat, or respiratory system; effects can be delayed
- Moderate concentrations – more severe eye and respiratory effects, headache, dizziness, nausea, coughing, vomiting and difficulty breathing.
- High concentrations – shock, convulsions, unable to breathe, coma, death; effects can be extremely rapid (within a few breaths).
Exposure limits
OSHA Permissible Exposure Limit (PEL): General Industry: 29 CFR 1910.1000 Z-2 Table -- Exposures shall not exceed 20 ppm (ceiling) with the following exception: if no other measurable exposure occurs during the 8-hour work shift, exposures may exceed 20 ppm, but not more than 50 ppm (peak), for a single time period up to 10 minutes.
Construction Industry: 29 CFR 1926.55 Appendix A -- 10 ppm, 15 mg/m3 TWA
Maritime: 29 CFR 1915.1000 Table Z-Shipyards -- 10 ppm, 15 mg/m3 TWA
American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV): 1 ppm, 14 mg/m3 TWA; 15 ppm, 21 mg/m3 STEL
National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL): 10 ppm, 15 mg/m3 Ceiling (10 Minutes).