This specification applies to the flameproof enclosure of electrical equipment. It prescribes constructional features necessary to ensure safety in service, the test requirements which the enclosure shall meet and the marking to be applied to the enclosure. The tests specified herein are intended as type tests. The enclosure is suitable for housing electrical apparatus in atmospheres where a mixture of air and flammable gas or vapour may occur. The specification provides for grouping of enclosures according to the dimensions of their gaps between joint surfaces, and an indication is given of the explosive gas atmosphere for which each group is appropriate. The specification does not at present apply to enclosure for explosive gas atmospheres for which safe gaps are smaller than those given in this specification. The specification does not apply to enclosure kept charged with air, or other non-flammable gas so as to prevent the entry of flammable ga. The specification does not apply to enclosure containing hydro-carbon oil and parts of equipment into which gaseous products from the oil may enter. This specification deals only with flameproof enclosure and not with other means of protection against an explosion hazard. These are covered by separate specifications.