What Is H2S Gas?

Hydrogen sulfide (a.k.a. hydrogen sulphide) gas occurs in natural gas deposits and other sources.
Hydrogen sulfide (a.k.a. hydrogen sulphide) gas occurs in natural gas deposits and other sources. (Image: David McNew/Getty Images News/Getty Images)

Hydrogen sulfide gas, with the chemical formula H2S, "is a colorless, flammable, extremely hazardous gas with a 'rotten egg' smell," according to the Occupational Health and Safety Administration (OSHA). It is found in manure pits and sewer lines as well as natural gas operations. It can cause a range of symptoms depending on the dose, from eye irritation to suffocation.

Why is H2S Dangerous?

Hydrogen sulfide is a naturally-occurring, flammable gas that can be formed from decaying organic matter. It is commonly found near raw sewage or animal manure. Because it is heavier than air, the gas will collect in confined spaces. According to Safety Directory, "Hydrogen sulfide has a very low odor threshold, with its smell being easily perceptible at concentrations well below 1 part per million (ppm) in air. The odor increases as the gas becomes more concentrated, with the strong rotten egg smell recognisable up to 30 ppm. Above this level, the gas is reported to have a sickeningly sweet odor up to around 100 ppm. However, at concentrations above 100 ppm, a person's ability to detect the gas is affected by rapid temporary paralysis of the olfactory nerves in the nose, leading to a loss of the sense of smell. This means that the gas can be present at dangerously high concentrations, with no perceivable odor."

What Does H2S Do to the Body?

At low concentrations and short exposures, H2S is an eye and lung irritant. It causes watering eyes, coughing or a sore throat. As concentration levels or exposure times increase, the irritation worsens and can include headaches and fluid in the lungs. High concentration levels can cause a coma or death from a few breaths.

Protection from H2S

Before entering an area where H2S gas can accumulate, the air should be tested. If H2S is detected, the space should be ventilated to remove the gas or lower the concentration to a safe level. If the space can not be adequately ventilated, properly trained individuals can work in the space if they follow OSHA rules for hazardous atmospheres in confined spaces.

Working in H2S Atmospheres

If a worker most work in an atmosphere contaminated with H2S gas, he must use a full-face respirator or a half-face respirator and tight-fitting goggles to protect both the eyes and the lungs from exposure. If the concentration of the gas is less than 100 parts per million, an air purifying respirator can be used. If the concentration of the gas is higher, a mask with a self contained air supply is mandatory. Rescuers cannot enter the contaminated space without appropriate protective equipment, so additional respirators should be kept on hand.

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