What is H2S?

Hydrogen sulfide, notated as H2S, is a toxic gas that can be recognized by its rotten egg smell. It can be found in places like sewers and swamps and has acquired the name sewer gas because of it. However, hydrogen sulfide can also be found in natural gas, volcanic gases, water sources, and even the human body (in very minute amounts). H2S is a byproduct of microbial decomposition of organic materials, this process is often referred to as anaerobic digestion due to the lack of oxygen during decomposition.

Aside from natural occurrences of H2S, it is often found in the petroleum industry, mining sites, wastewater treatment plants, agricultural sites, paper processing plants, and more. At the frequency of hydrogen sulfide’s presence in certain occupations, employees need to be aware of the risks that the toxic gas poses to their health. The first thing to know is the lower explosive limit and the upper explosive limit (LEL and UEL) of H2S gas. The ratio of H2S saturation in air between those limits is known as the flammable range, for hydrogen sulfide that range is 4.3-46%. Serious injuries and even death can result from these types of toxic and flammable gas explosions in areas like confined spaces since the gas has no way of dispersing itself. It often collects in areas that are not well ventilated and with the gas being heavier than air, it pools in areas such as basements and sewers. If exposed to hydrogen sulfide never rely on your sense of smell to tell if it is gone. The gas can deaden your sense of smell after mere seconds if the concentration is high enough. This makes going into areas where H2S is present incredibly dangerous since the LEL is so low at 4.3%.

On top of being flammable, hydrogen sulfide is also an irritant and chemical asphyxiant that causes problems with the body’s nervous system and oxygen utilization. At low exposures the gas causes the eyes to burn and irritates the throat and lungs. At higher levels of exposure, the victim may experience convulsions, shock, the inability to breathe, rapid unconsciousness, coma, and even death. These symptoms can occur in just one breath of air saturated with the gas.


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