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OSHA Regulations for H2S

In addition to its foul, rotten-egg stench, hydrogen-sulfide (H2S) gas is flammable and can lead to asphyxiation at concentrations above 500 parts-per-million (ppm). To protect workers, the U.S. Occupational Safety and Health Administration has developed a set of basic guidelines and emergency protocols for dealing with incidents that involve hydrogen sulfide.

  1. Permissible Exposure Limit (PEL)

    • OSHA defines the Permissible Exposure Limit (PEL) of a substance as the maximum concentration that workers can be continually exposed to for an entire 8-hour work day. Currently, OSHA has established specific hydrogen-sulfide PELs for three industries. For the construction industry the PEL is set at 10 ppm and for the maritime industry (i.e. shipyards) at 10 ppm. For all other industries, however, the PEL for hydrogen sulfide is set slightly higher, at 20 ppm.

    Maximum Peak Exposure

    • OSHA defines maximum peak exposure as the maximum safe levels of a substance that a worker can be exposed to for a single 10-minute period during an 8-hour workday. However, maximum peak exposure only refers to situations in which there is zero exposure to the substance for the other 7 hours and 50 minutes of the day. For hydrogen sulfide, that level is 50 ppm.

    Immediately Dangerous to Life and Health (IDLH)

    • For the safety of rescuers or repair crews, OSHA and the National Institute for Occupational Safety and Health (NIOSH) define the point at which substances are Immediately Dangerous to Life and Health. IDLH, as it's known, is the minimum level at which a full-face respirator connected to either an auxilary air supply or self-contained breathing apparatus (SCBA) is required before entering the toxic environment. For hydrogen sulfide, the IDLH is 100 ppm.

    Testing Protocols

    • Hydrogen sulfide has a distinctive foul odor that can be sensed even at 5 parts per billion. However, the danger of relying on smell to gauge hydrogen-sulfide levels is that the gas causes olfactory fatigue at concentrations below PEL. In other words, the nose becomes overpowered by the gas and stops sensing it completely. So instead a trained technician must sample the air with a hydrogen-sulfide detector tube. OSHA currently approves three types of detector tubes: the Dräger Hydrogen Sulphide 1/d, the Gastec 4LL and the Matheson-Kitagawa 8014-120SD.

    Decontamination

    • To remove hydrogen-sulfide buildup, the space must be continually ventilated until the gas returns to proper levels. If the facility is equipped with exhaust fans, removal simply involves evacuating the area, opening air flow and running the fans until the gas dissipates. If the facility does not have an installed exhaust system, an air pump might be necessary.

      Since hydrogen-sulfide gas has a greater density than air, it tends to sink and collect in low elevations. Draining the gas with a special vacuum pump can expedite the process. Similarly, if there is a fire risk, the vacuum pump can be coupled with a second device that pumps inert gas into the area.

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