SCHEDULE 2 Essential health and safety requirements relating to the design and construction of equipment and protective systems intended for use in potentially explosive atmospheres

2.1.1.3 Explosive atmospheres caused by gases, vapours or hazes
Equipment must be so designed that the opening of equipment parts which might be sources of ignition is possible only under non-active or intrinsically safe conditions. Where it is not possible to render equipment non-active, the manufacturer must affix a warning label to the opening part of the equipment.
If necessary, equipment must be fitted with appropriate additional interlocking systems.