Specifies the general requirements for construction, testing and marking of electrical apparatus and Ex components intended for use in explosive gas atmospheres. Electrical apparatus complying with this standard is intended for use in hazardous areas in which explosive gas atmospheres, caused by mixtures of air and gases, vapours or mists, exist under normal atmospheric conditions. The significant changes with respect to the previous edition are: Requirements for explosive dust atmospheres transferred from IEC 61241-0, The marking Group "II" alone has been replaced by "IIA", "IIB", or "IIC" as many of the enclosure requirements are now aligned with a specific sub-group, Dust groups defined as Group IIIA, IIIB and IIIC, Remainder of "electrostatic" requirements transferred from IEC 60079-26 and Equipment protection levels (EPL) introduced. The contents of the interpretation sheet 1 of November 2008 and corrigendum 1 of December 2010 have been included in this copy.