Recommendation ITU-T K.78 specifies the radiated and conducted immunity requirements against a high altitude electromagnetic pulse (HEMP) for equipment installed in telecommunication centres for functions such as switching, transmission, radiocommunication, and power distribution. The requirements consist of immunity test methods and levels for telecommunication equipment in each installation condition. Immunity levels can be improved by applying a protection concept of surge protective devices (SPDs) for surge mitigation and electromagnetic screening to the building and equipment enclosures.