Hydrogen Sulfide, or H2S, is a toxic gas that is colorless and highly flammable. Other names for H2S include sewer gas, swamp gas, manure gas and stink damp. In addition to gas form, H2S can exist as a liquid compressed gas.
Where H2S Is Found
H2S gas occurs naturally in hot springs, crude petroleum, natural gas and as a byproduct of decaying/decomposing organic material. However, it is also encountered in a diverse number of industries such as wastewater treatment, oil & gas drilling, refining, mining, pulp & papermill processing, agriculture, canneries, and construction. H2S is slightly denser than air, so it can collect in ground, low-lying, or below-ground areas such as tunnels, basements, manholes, sewer lines, and utility vaults.
Your Sense of Smell and H2S
The primary route H2S enters the body is through inhalation. H2S smells like rotten eggs and can be smelled at very low concentrations in air. The smell should be a warning that the gas is present—H2S can be fatal, even at much lower concentrations than other hazardous gases. However, due to olfactory fatigue, at low concentrations or high concentrations, people can lose the ability to smell the gas. Repeated exposure to the gas can cause people to have reactions at progressively lower levels. Because of this, you should never rely on your sense of smell to indicate the ongoing presence of H2S. Instead, use proper testing and monitoring devices to detect H2S.
Health Effects of H2S Exposure
H2S is a chemical asphyxiant and irritant, so it affects the amount oxygen your lungs can use while irritating the respiratory tract and central nervous system. Symptoms can occur within taking only 1-2 breaths of H2S.
Low Levels of H2S Can Cause:
- Eye/nose/throat/lung irritation
- Watering eyes
- Cough
- Shortness of breath
- Headache
- Fatigue
- Digestive disturbances
- Insomnia
- Irritability
Moderate Concentrations of H2S Can Cause:
- Severe eye and respiratory irritation
- Coughing
- Difficulty breathing
- Accumulation of fluid in the lings
- Headache
- Dizziness
- Nausea
- Vomiting
- Staggering
- Excitability
High Concentrations of H2S Can Cause:
- Shock
- Convulsions
- Inability to breathe
- Instantaneous lack of consciousness
- Coma
- Death
- Protection Against H2S Exposure
H2S and Confined Spaces
Your workplace may have confined spaces where there is H2S. Before entering an area where H2S may be present:
A qualified person must test the air using monitoring equipment such as H2S detector tubes or a multigas meter. Testing should also determine if fire/explosion precautions are necessary.
If the gas is present, the space/area must be continually ventilated to remove the gas.
If the gas cannot be removed, the worker entering the space must use appropriate personal protective, rescue, and communication equipment.
Workers must be monitored for overexposure. When in doubt about monitoring and entering confined spaces, reference OSHA’s Confined Space Standard.
Entering Dangerous H2S Atmospheres
H2S gas 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 SCBA with 30 min. minimum service life 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 with an H2S filter cartridge/canister may be used with a full facepiece respirator. If a half-mask respirator is used, tight-fitting goggles must also be used to prevent eye irritation.
Summary
If H2S is present at your workplace, there should be health and safety practices in place. Make sure to learn all you can about H2S and be properly trained and suited up before entering a hazardous environment.
BE AWARE…H2S CAN BE DEADLY!
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