Hydrogen sulfide gas occurs naturally in crude petroleum, natural gas, volcanic gases and hot springs. It also can result from bacterial breakdown of organic matter and be produced by human and animal wastes.
Hydrogen Sulfide is a colorless, flammable and toxic gas. In low concentrations, it has the smell of rotten eggs. In high concentrations it is odorless. H2S is heavier than air, so it tends to accumulate at the bottom of poorly ventilated spaces. Although very pungent at first, it quickly deadens the sense of smell, so potential victims may be unaware of its presence until it is too late.
Health and safety Applications
Low-level exposure often is more chronic in nature and usually is seen in industrial settings. Chronic low-level exposure results primarily in irritation to mucous membranes and the respiratory system. Patients exposed to continuous low-level concentrations or after acute exposure to the very high concentrations of hydrogen sulfide can lose their ability to smell/detect the gas even though it is still present in the environment (olfactory fatigue/paralysis).
- 0.0047 ppm is the recognition threshold, the concentration at which 50% of humans can detect the characteristic odor of hydrogen sulfide, normally described as resembling "a rotten egg".
- 10-20 ppm is the borderline concentration for eye irritation.
- 50-100 ppm leads to eye damage.
- At 150-250 ppm the olfactory nerve is paralyzed after a few inhalations, and the sense of smell disappears, often together with awareness of danger.
- 320-530 ppm leads to pulmonary edema with the possibility of death.
- 530-1000 ppm causes strong stimulation of the central nervous system and rapid breathing, leading to loss of breathing;
- 800 ppm is the lethal concentration for 50% of humans for 5 minutes exposure(LC50).
- Concentrations over 1000 ppm cause immediate collapse with loss of breathing, even after inhalation of a single breath.
Pipeline Applications
Hydrogen Sulfide when in contact with Carbon Steel reacts and forms Iron Sulfide. Iron Sulfide is formed when Iron Oxide is exposed to Hydrogen Sulfide. When Iron Sulfide is exposed to air, it is oxidized back to iron oxide and either free sulfur or sulfur dioxide gas. This reaction between iron sulfide and oxygen is accompanied by the generation of a considerable amount of heat. In fact, so much heat is released that individual particles of iron sulfide become incandescent. This rapid exothermic oxidation with incandescence is known as pyrophoric oxidation and it can ignite nearby flammable hydrocarbon-air mixtures.
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