This technical report defines how protective devices for High Altitude Nuclear Electromagnetic Pulse (HEMP) protection of civilian systems are specified. Performance requirements will be given in future IEC standards. This technical report is intended to be used for the harmonization of existing or future specifications issued by protective devices manufacturers, electronic equipment manufacturers, administrative bodies and other buyers. This technical report covers protective devices currently used for protection against HEMP radiated EM fields. In general, parameters relevant to HEMP, that is parameters related to very fast changes of EM fields, as a function of time, are dealt with.