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Hydrogen Sulfide in Workplaces

Hydrogen sulfide is produced naturally from decaying organic matter. It can be released from sewage sludge, liquid manure, and sulfur hot springs, and with natural gas. It is also used or is a by-product in many industrial processes such as:

  • Petroleum production and refining
  • Sewer and wastewater treatment
  • Agricultural silos and pits
  • Textile manufacturing
  • Pulp and paper processing
  • Food processing
  • Hot asphalt paving
  • Mining

Many workers are at risk for exposure to hydrogen sulfide, especially when working in confined spaces. For example,

  • Sanitation workers can be exposed when cleaning or maintaining municipal sewers and septic tanks.
  • Farm workers can be exposed when cleaning manure storage tanks or working in manure pits.
  • Workers in oil and natural gas drilling and refining may be exposed because hydrogen sulfide may be present in oil and gas deposits and is a by-product of the desulfurization process of these fuels. See OSHA Oil and Gas Well Drilling and Servicing eTool.

In general, working in the following areas and conditions increases a worker’s risk of overexposure to hydrogen sulfide:

  • Confined spaces (for example pits, manholes, tunnels, wells) where hydrogen sulfide can build up to dangerous levels.
  • Windless or low-lying areas that increase the potential for pockets of hydrogen sulfide to form.
  • Marshy landscapes where bacteria break down organic matter to form hydrogen sulfide.
  • Hot weather that speeds up rotting of manure and other organic materials, and increases the hydrogen sulfide vapor pressure.

OSHA Safety and Health Information Bulletins (SHIBs)

Recent OSHA Citations




Hydrogen Sulfide Can
Kill Workers

A 49-year old sanitation worker died when rescuing a co-worker from an underground sewer vault when he was overcome with hydrogen sulfide gas.

Workers who entered a 27-foot deep pit in a marshy area died after being overcome by hydrogen sulfide.

Workers died clearing debris from an underground sewer pipe. Both were overwhelmed by hydrogen sulfide gas. They were 19 and 25 years old.

Two workers died at an oil field water injection plant while replacing a water transfer pump. Hydrogen sulfide was released when a clamp was removed.

A 25-year old waste hauling service worker died after collapsing in an underground manure waste pit. The pit had a square access opening fitted with a removable stainless steel cover. The pit was not equipped with any type of ventilation system or gas monitoring equipment.

Four workers died in an underground lift station that collected leachate from a landfill. One worker entered to replace a sump pump and was overcome by hydrogen sulfide gas. A second, then third, and finally fourth worker entered to attempt rescue. All were overcome and died in the permit-required confined space. A permit entry system had not been established.

Storage silos 12 feet in diameter 40 feet high with access door at grade level

Example of a confined space – storage silo.

Conveyor Access Pit

Example of a confined space – vault.

Lift Station Wet Well

Example of a confined space – vault.

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