Gives guidance on the design, construction and use of electrical apparatus in explosive gas atmospheres in which: 1.a protective gas (air or inert gas), maintained at a pressure above that of the external atmosphere, is used to guard against the formation of an explosive mixture within enclosures which do not contain a source of flammable gas or vapour; and/or 2.a protective gas, in sufficient quantity to ensure that the resultant mixture concentration around the electrical parts is well below the value of the lower explosive limit appropriate to the particular conditions of use, is supplied to an enclosure containing one or more sources of flammable gas or vapour to guard against the formation of an explosive mixture. In this case, as an alternative, protection may be achieved by maintaining an inert protective gas within the enclosure at a pressure above that of the external atmosphere. Includes recommendations for the apparatus and its associated equipment (including the inlet and exhaust ducts) and also for the auxiliary control apparatus necessary to ensure that pressurization and/or dilution is established and maintained. Recommendations for marking are also made. This publication has the status of a technical report.