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Hydrogen sulfide (H2S) is a toxic gas with an offensive odour reminiscent of rotten eggs. There is the potential for widespread occupational exposure to H2S, including in the oil and water treatment industries. There is a particular concern for exposure in confined spaces such as manholes and sewer pipes; the high concentrations that can build up in such conditions (> 1000 parts per million (ppm)) can lead to the rapid development (within minutes) of unconsciousness and death. There are many reports throughout the literature of fatalities caused by exposure to H2S. However, there is also a concern for adverse health effects caused by day to day occupational exposures to low concentrations (< 10 ppm); this is because H2S selectively binds to the enzymes involved in cellular respiration thereby causing a shift towards anaerobic respiration. The recently revised UK occupational exposure limits for H2S are designed to protect against the development of such effects.
SETTING OCCUPATIONAL EXPOSURE LIMITS FOR H2S
The purpose of this paper is to outline the evidence and rationale underpinning the recently updated UK occupational exposure limits (OELs) for H2S. To place this information in context it is helpful to have an understanding of the UK regulatory framework surrounding OELs. A previous paper in this series has already covered this topic.1 Box 1 and fig 1 summarise the key features involved in OEL setting in the UK. The reason why the OELs for H2S were recently reviewed in the UK is because in the mid 1990s a series of human volunteer studies were published that suggested exposures as low as 10 ppm might cause a shift to anaerobic metabolism under conditions of physical exertion. This leads to a concern for adverse physiological effects at what were at the time …