Understanding Hydrogen Sulfide (H2S)
Hydrogen Sulfide (H2S) is a colorless gas. It is heavier than air, flammable, explosive, corrosive, and very poisonous. Its foul odor has characteristics of rotten eggs, which is perceptible at very low concentrations. However, in higher concentrations, H2S affects a person’s ability to smell the toxic gas the longer the person is exposed. In severe cases, a person may eventually not realize they are inhaling the toxic gas until it is too late. Hydrogen Sulfide often results from the bacterial breakdown of organic matter in the absence of oxygen, such as in swamps and sewers. It also naturally occurs in manure pits, well water, oil and gas wells, and volcanoes.
The primary route of exposure is inhalation and the hazardous gas is rapidly absorbed by the lungs. In addition, hydrogen sulfide is highly flammable and gas/air mixtures can be explosive. It can potentially travel to sources of ignition and flash back. If ignited, the gas burns to produce toxic vapors and gases, such as Sulfur Dioxide.
Because it is heavier than air, hydrogen sulfide can travel and collect in low-lying and enclosed, poorly-ventilated areas such as manholes, sewers, and underground telecommunication site vaults. For work within enclosed spaces, appropriate procedures for identifying hazards, monitoring, and entering confined spaces must be defined. Hydrogen Sulfide presence makes work in enclosed spaces potentially very dangerous.
When present in high concentrations, Hydrogen Sulfide may produce these symptoms:
- Eye, throat, respiratory irritation
- Olfactory fatigue (loss of smell)
- Pulmonary edema (excess fluid in lung tissue)
When researching H2S gas detection solutions, facility managers should be aware of the following H2S exposure limits:
|20 ppm (ceiling)||OSHA PEL (General Industry)|
|10 ppm TWA||OSHA PEL (Construction Industry)|
|10 ppm TWA||OSHA PEL (Maritime)|
|10 ppm TWA, 15 ppm STEL||ACGIH TLV|
|10 ppm ceiling (10 minutes)||NIOSH REL|
|100 ppm||NIOSH IDLH|