Hydrogen sulfide

Figure 1. A ball and stick model of hydrogen sulfide. The white balls are hydrogen and the yellow ball is sulfur.

Hydrogen sulfide is a chemical with the formula H₂S. Hydrogen sulfide is a dangerous, colourless gas that occurs naturally in many petroleum products but can make up significant amounts of natural gas. It has a distinct "rotten egg" smell. In addition to being harmful to human health as an asphyxiant, hydrogen sulfide is both flammable and explosive.

Hydrogen sulfide can exist naturally or be produced by human activities. For example, hydrogen sulfide occurs naturally in crude oil, natural gas, and in hot springs. Bacterial breakdown of human and animal waste also produced hydrogen sulfide. Humans release hydrogen sulfide through petroleum drilling and refining, wastewater treatment, and paper mills.

Some additional properties of hydrogen sulfide are outlined in the table below.

Chemical formula	H2S
Molar mass	34.0809 grams/mole
Melting point	-82oC
Boiling point	-60oC

The hydrogen sulfide content of natural gas is one of the main safety concerns associated with the use of the gas. Natural gas with especially high levels of hydrogen sulfide is referred to as sour gas. Some of this sulfur can be removed through a "sweetening" process, which is done mainly using amine solutions that remove this hydrogen sulfide. The process used is known as the "amine process" or more commonly the "Girdler process", and it is used in most gas sweetening operations.

Uses

Hydrogen sulfide is used primarily to produce sulfuric acid and sulfur. Hydrogen sulfide is also used to create a variety of inorganic sulfides used to create pesticides, leather, dyes, and pharmaceuticals. Additionally, hydrogen sulfide is used to produce heavy water for nuclear power plants (like CANDU reactors specifically). Hydrogen sulfide can also be used in agriculture as a disinfectant. It is also widely used in chemical analysis.

Iron smelters, landfills, food processing plants, and breweries are some examples of industrial sources that produce or use hydrogen sulfide. The gas must be disposed of properly as emissions of hydrogen sulfide can be dangerous.

Health Effects

The health effects of inhalation of hydrogen sulfide depend on how much a person is exposed to. Hydrogen sulfide is dangerous even at relatively small concentrations as it acts as both an irritant and asphyxiant. At relatively low concentrations, hydrogen sulfide irritates the eyes, nose, and throat. These effects are especially dangerous for children and people with reduced lung function.

At certain concentrations, exposure to hydrogen sulfide can result in unconsciousness in 1-2 breaths or even near instant death. In concentrations as low as 500-700 ppm, hydrogen sulfide can result in death within an hour. At concentrations of only 1000-2000 ppm, hydrogen sulfide can cause near instant death. Health effects of exposure include headaches, memory loss, and problems with the cardiovascular system. Repeated exposure to hydrogen sulfide can result in eye inflammation, fatigue, irritability, insomnia, and weight loss.