May 2010
Springer 2010 – Applied Microbiology and Molecular Biology in Oilfield Systems
Chapter 18, pp 151–157
ISBN 978-90-481-9252-6
Journal
Chapter 18 – Problems Caused by Microbes and Treatment Strategies – Health and Safety Issues from the Production of Hydrogen Sulphide
Hydrogen sulphide (H2S) is a colourless, transparent gas that is heavier than air (SG = 1.18). It is extremely flammable and is explosive across a very wide range of concentrations 4.3-46% by volume in air (in comparison, methane is explosive at 5–15% volume in air). The boiling point of hydrogen sulphide is -60°C and so it exists as a gas at standard conditions; it burns with a blue flame to produce water and sulphur dioxide, which is also a very toxic gas. At low concentrations hydrogen sulphide has a very pungent smell, typically described as ‘rotten eggs’; at higher concentrations it can become sickly sweet. Hydrogen sulphide can he easily identified by its smell at very low concentrations, detectable down to 0.0047 ppm (HSE, 2009), However, smell alone cannot he relied upon to detect the continued presence of hydrogen sulphide. At high concentrations, or after sustained exposure to lower concentrations, hydrogen sulphide becomes undetectable by smell as it rapidly paralyses the olfactory nerve.
The health and safety concerns generated by the presence of hydrogen sulphide arc twofold: first, poisoning from the direct inhalation of hydrogen sulphide gas and, second, the risk posed to the integrity of equipment due to the reaction of hydrogen sulphide with metals. The potential for sudden failure of metalwork as a result of sulphide stress corrosion cracking is a serious safety risk to personnel and also an environmental hazard. The solubility of hydrogen sulphide in water is approximately 4 g/1 at 20°C and so it is soluble in the bloodstream and can he quickly transported around and react with the body after inhalation. Its solubility in water also enhances its corrosive potential as it will readily partition into any small volume of water present in a system. At typical produced water pHs of 6–7 the speciation of sulphide in water is such that more than 50% of it is present in the form of H2S (the remainder being HS-), this drops to 10% as the pH rises to 8.
