Term Main definition
Hydrogen Sulfide, (H2S)
A colourless, highly toxic, highly flammable gas with a characteristic pungent odour of rotten eggs. Hydrogen sulfide is most tightly associated with oil and gas extraction and refinement because H2S occurs naturally in crude oil in small amounts, while it can also occur in natural gas in large concentrations. Also, petroleum is desulfurized by converting the sulfuric compounds into H2S by adding hydrogen. While most people are able to smell H2S at concentrations as low as 0.47 ppb (0,00047 ppm), at concentrations above 100-150 ppm it quickly deadens the sense of smell, so victims may be unaware of its presence until it is too late. H2S is detectable with colorimetric tubes that are available from many manufacturers in a wide range of target concentrations. There are many electronic instruments available that can measure the concentration of H2S through an electrochemical cell. Hydrogen sulfide sensors are among the most widely used sensors for toxic gases in multigas instruments, in addition to oxyge- and combustibles sensors.