DSEAR (The Dangerous Substances and Explosive Atmospheres Regulations of 2002) is the United Kingdom's implementation of the European Union-wide ATEX directive.
The intention of the Regulation is to reduce the risk of a fatality or serious injury resulting from a "dangerous substance" igniting and potentially exploding. Examples of a "dangerous substance" as defined by DSEAR include sawdust, ethanol vapours, and hydrogen gas. The regulation is enforceable by the HSE or local authorities.
References
DSEAR Wikipedia(Text) CC BY-SA