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Hydrogen sulfide (also known as H2S, sewer gas, swamp gas, stink damp, and sour damp) is a colorless gas known for its pungent "rotten egg" odor at low concentrations. It is extremely flammable and highly toxic.

Hydrogen sulfide is used or produced in a number of industries, such as

  • Oil and gas refining
  • Mining
  • Tanning
  • Pulp and paper processing
  • Rayon manufacturing

Hydrogen sulfide also occurs naturally in sewers, manure pits, well water, oil and gas wells, and volcanoes. Because it is heavier than air, hydrogen sulfide can collect in low-lying and enclosed spaces, such as manholes, sewers, and underground telephone vaults. Its presence makes work in confined spaces potentially very dangerous.

The health effects of hydrogen sulfide depend on how much H2S a worker breathes and for how long. However, many effects are seen even at low concentrations. Effects range from mild, headaches or eye irritation, to very serious, unconsciousness and death.

This web page provides information on how hydrogen sulfide can affect your health, where you might find it, and how to prevent harmful exposures.

How do I find out about employer responsibilities and worker rights?

Workers have a right to a safe workplace. The law requires employers to provide their employees with working conditions that are free of known dangers.

OSHA can help answer questions or concerns from employers and workers. To reach your regional or area OSHA office, go to OSHA's Regional & Area Offices web page or call 1-800-321-OSHA (6742).

Small Business employers may contact OSHA's free and confidential on-site consultation service to help determine whether there are hazards at their worksites and work with OSHA on correcting any identified hazards. On-site consultations services are separate from enforcement activities and do not result in penalties or citations. To contact OSHA's free consultation service, go to OSHA's On-site Consultation web page or call 1-800-321-OSHA (6742) and press number 4.

Workers may file a complaint to have OSHA inspect their workplace if they believe that their employer is not following OSHA standards or that there are serious hazards. Employees can file a complaint with OSHA by calling 1-800-321-OSHA (6742) or by printing the complaint form and mailing or faxing to your local OSHA area office. Complaints that are signed by an employee are more likely to result in an inspection.

If you think your job is unsafe or you have questions, contact OSHA at 1-800-321-OSHA (6742). It's confidential. We can help. For other valuable worker protection information, such as Workers' Rights, Employer Responsibilities, and other services OSHA offers, visit OSHA's Workers' page.

Highlights

Hydrogen sulfide is one of the leading causes of workplace gas inhalation deaths in the United States. According to the Bureau of Labor Statistics (BLS), hydrogen sulfide caused 60 worker deaths between 2001 and 2010.

Why is hydrogen sulfide so deadly?

  • It is highly flammable and toxic, even at low concentrations.
  • It is heavier than air and may travel along the ground.
  • It can build up in low-lying areas, and in confined spaces (including enclosed, poorly ventilated areas, such as manure pits, sewers, manholes, and underground vaults).
  • After a while at low or more quickly at high concentrations, you can no longer smell it to warn you it's there.
  • It can quickly, almost immediately, overcome unprepared workers, including rescue workers.

*Accessibility Assistance: Contact OSHA's Directorate of Technical Support and Emergency Management at (202) 639-2300 for assistance accessing PDF materials.

All other documents, that are not PDF materials or formatted for the web, are available as Microsoft Office® formats and videos and are noted accordingly. If additional assistance is needed with reading, reviewing or accessing these documents or any figures and illustrations, please also contact OSHA's Directorate of Technical Support and Emergency Management at (202) 639-2300.

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