What is the Acceptable Short-Term Exposure for H2S?

The actual term, according to the American Council of Government Industrial Hygienists (ACGIH), is Threshold Limit Value-Short Term Exposure Limit (TLV-STEL). Short-Term Exposure Limit, or STEL, is used in common language.

The TLV-STEL for hydrogen sulfide (H₂S), CAS Registry Number 7783-06-04 is listed in the ACGIH Publication as: STEL 5 parts per million (PPM).

According to NIOSH, H₂S is a colorless gas with a strong odor of rotten eggs. Exposure to hydrogen sulfide may cause irritation to the eyes and respiratory system. It can also cause apnea, coma, convulsions, dizziness, headache, weakness, irritability, insomnia, stomach upset, and, if liquid: frostbite. Workers may be harmed from exposure to hydrogen sulfide. The level of exposure depends upon the dose, duration, and work being done.

(Learn about Working With Hydrogen Sulfide.)

This TLV-STEL for hydrogen sulfide references a 15 minute Time Weighted Average (TWA) exposure that should not be exceeded during a workday.

The ACGIH further states that this level of exposure should not be exceeded even if the 8 hour TWA is within the TLV-TWA. For reference purposes, please note that the TWA for an 8 hour period for hydrogen sulfide is 1ppm.

The TLV-STEL is considered a supplemental measurement to the TLV-TWA for an 8 hour workday. Any exposures above 1ppm in this case (the TLV-TWA 8-hour for hydrogen sulfide) and up to 5ppm (the TLV-STEL), should be less than 15 minutes and occur no more than 4 times per day. There should be at least 60 minutes between any successive exposures in this range.

Safety professionals understand that H₂S is a deadly chemical, and is common in workplaces such as rayon textile manufacture, the petroleum and gas industry, sewers, and in agricultural/manure storage areas and landfills.

(Read more about the New Hydrogen Sulfide Regulations: What You Need to Know.)

Please remember that the ACGIH publishes its work as guidelines "to assist in the control of health hazards." That means that this is not a hard and fast standard, or indicative of what all workers may be exposed to. We understand, in this safety business, particularly in respect to chemical and biological exposures in the workplace, that each worker is different, as are their tolerances and reactions to any exposure.

Please ensure that you rely on the hierarchy of controls and the advice of Industrial Hygiene professionals when doing hazard analysis that involves any potential chemical or biological exposures. With chemicals like H₂S, there is absolutely no margin for error.

The ACGIH list H₂S, at 100ppm, as Immediately Dangerous to Life and Health (IDLH). No margin for error indeed.