H2S, also known as hydrogen sulfide (sometimes seen as hydrogen sulphide), is a colorless, sometimes flammable gas that usually has a characteristic foul smell of rotten eggs. You may not be able to see it, but you can certainly smell it. Hydrogen sulfide is caustic, corrosive, and poisonous.
The odor comes from the bacterial break down of sulfites in organic matter in the absence of oxygen, locations such as in swamps and sewers. It can also occur in some volcanic gases or natural gas. Hydrogen sulfide’s characteristic smell is usually associated with sulfur, but this is a common mistake. Elemental sulfur has no signature smell. Although the smell of hydrogen sulfide can initially be very strong, over time will become much weaker or may even become undetectable. The nose won’t again register the smell until after it has been away from it for a short time. This is known as olfactory fatigue. As a result, anyone exposed to hydrogen sulfide may assume that there is no danger because they can no longer smell the offensive odor of the gas. However, there still is a great amount of danger.
Hydrogen sulfide is very poisonous. It is what’s known as a broad-spectrum poison, which means that it can affect several different systems in the body at once, although the nervous system is generally the most often affected. Hydrogen sulfide has an effect on the body similar to carbon monoxide, only worse. Initial signs of exposure include eye irritation, nausea, cough, sore throat, and shortness of breath. These symptoms can last for up to a few weeks. Long term exposure to low levels of hydrogen sulfide can include fatigue, headaches, irritability, memory loss, and loss of appetite. Exposures to high levels of hydrogen sulfide, even for only a short time, have a high probability of death.
Different levels of hydrogen sulfide in the surrounding atmosphere have different affects on the human body. Levels of 10-20 parts per million will irritate the eyes, while 50-100 parts per million can lead to eye damage. It is around this level, 100-150 parts per million that olfactory fatigue begins after just a few inhalations. Above 320 parts per million begins to cause serious damage. 800-1000 parts per million is considered lethal exposure. Safety organizations around the world have set maximum allowable exposure limit for a safe working environment.
There are several types of devices used for the detection and measuring of hydrogen sulfide. A portable or fixed gas detector can be used to determine the levels. Hydrogen sulfide detectors will sound alarms when gas levels in the surrounding area become dangerous. Most portable H2S alarms will sound at levels as low as 10 parts per million.