Contact with liquid hydrogen sulfide causes

frostbite. If clothing becomes wet with the

liquid, avoid ignition sources, remove the

clothing and isolate it in a safe area to allow

the liquid to evaporate.

Health effects of H2S exposure 

Hydrogen sulfide is both an irritant and a

chemical asphyxiant with effects on both

oxygen utilization and the central nervous

system. Its health effects can vary depending

on the level and duration of exposure.

Repeated exposure can result in health effects

occurring at levels that were previously tolerated without any effect.

Low concentrations irritate the eyes, nose,

throat and respiratory system (e.g., burning/

tearing of eyes, cough, shortness of breath).

Asthmatics may experience breathing difficulties. The effects can be delayed for several

hours, or sometimes several days, when

working in low-level concentrations. Repeated

or prolonged exposures may cause eye

inflammation, headache, fatigue, irritability,

insomnia, digestive disturbances and weight

loss. 

Moderate concentrations can cause more

severe eye and respiratory irritation (including

coughing, difficulty breathing, accumulation

of fluid in the lungs), headache, dizziness,

nausea, vomiting, staggering and excitability.

Hazardous properties of H2S gas 

Hydrogen sulfide is heavier than air and may

travel along the ground. It collects in low-lying

and enclosed, poorly-ventilated areas such as

basements, manholes, sewer lines, underground telephone vaults and manure pits.

For work within confined spaces, use appropriate procedures for identifying hazards,

monitoring and entering confined spaces.

The primary route of exposure is inhalation

and the gas is rapidly absorbed by the lungs.

Absorption through the skin is minimal.

People can smell the “rotten egg” odor of

hydrogen sulfide at low concentrations in air.

However, with continuous low-level exposure, or at high concentrations, a person

loses his/her ability to smell the gas even

though it is still present (olfactory fatigue).

This can happen very rapidly and at high

concentrations, the ability to smell the gas

can be lost instantaneously. Therefore, DO

NOT rely on your sense of smell to indicate

the continuing presence of hydrogen sulfide

or to warn of hazardous concentrations.

In addition, hydrogen sulfide is a highly flammable gas and gas/air mixtures can be explosive. It may travel to sources of ignition and

flash back. If ignited, the gas burns to produce toxic vapors and gases, such as sulfur

dioxide. 

FactSheet

Hydrogen Sulfide (H2S)

Hydrogen sulfide is a colorless, flammable, extremely hazardous gas with a “rotten egg” smell. Some common names for the gas include sewer gas, stink damp,

swamp gas and manure gas. It occurs naturally in crude petroleum, natural gas,

and hot springs. In addition, hydrogen sulfide is produced by bacterial breakdown of organic materials and human and animal wastes (e.g., sewage).

Industrial activities that can produce the gas include petroleum/natural gas

drilling and refining, wastewater treatment, coke ovens, tanneries, and kraft

paper mills. Hydrogen sulfide can also exist as a liquid compressed gas.
This is one in a series of informational fact sheets highlighting OSHA programs, policies or 

standards. It does not impose any new compliance requirements. For a comprehensive list of 

compliance requirements of OSHA standards or regulations, refer to Title 29 of the Code of Federal

Regulations. This information will be made available to sensory impaired individuals upon request.

The voice phone is (202) 693-1999; teletypewriter (TTY) number: (877) 889-5627.

U.S. Department of Labor

www.osha.gov

(800) 321-OSHA

For more complete information:

DSG 10/2005

High concentrations can cause shock, convulsions, inability to breathe, extremely rapid

unconsciousness, coma and death. Effects

can occur within a few breaths, and possibly

a single breath.

Protection against H2S exposure 

Before entering areas where hydrogen sulfide may be present:

1. Air must be tested for the presence and

concentration of hydrogen sulfide by a

qualified person using air monitoring

equipment, such as hydrogen sulfide

detector tubes or a multi-gas meter that

detects the gas.

Testing should also determine if fire/

explosion precautions are necessary.

2. If the gas is present, the space/area must

be ventilated continually to remove the

gas.

3. If the gas cannot be removed, the person

entering the space/area must use appropriate respiratory protection and any

other necessary personal protective

equipment, rescue and communication

equipment.

OSHA’s Confined Spaces standard contains specific requirements for identifying,

monitoring and entering confined spaces.

Entering dangerous H2S atmospheres

A level of H2S gas at or above 100 ppm is

Immediately Dangerous to Life and Health

(IDLH). Entry into IDLH atmospheres can only

be made using: 1) a full facepiece pressure

demand self-contained breathing apparatus

(SCBA) with a minimum service life of thirty

minutes, or 2) a combination full facepiece

pressure demand supplied-air respirator with

an auxiliary self-contained air supply. 

If H2S levels are below 100 ppm, an air-purifying respirator may be used, assuming the

filter cartridge/canister is appropriate for

hydrogen sulfide. A full facepiece respirator

will prevent eye irritation.

If air concentrations are elevated, eye irritation may become a serious issue. If a halfmask respirator is used, tight fitting goggles

must also be used.

Workers in areas containing hydrogen sulfide

must be monitored for signs of overexposure. 

NEVER attempt a rescue in an area that may

contain hydrogen sulfide without using

appropriate respiratory protection and without being trained to perform such a rescue.