This part of International Standard IEC 61331 applies to materials in sheet form used for the manufacturing of PROTECTIVE DEVICES against X-RADIATION of RADIATION QUALITIES generated with X-RAY TUBE VOLTAGES up to 400 kV and gamma radiation emitted by radionuclides with photon energies up to 1,3 MeV. This part 1 is not intended to be applied to PROTECTIVE DEVICES when these are to be checked for the presence of their ATTENUATION properties before and after periods of use. This part 1 specifies the methods of determining and indicating the ATTENUATION properties of the materials. The ATTENUATION properties are given in terms of: - ATTENUATION RATIO; - BUILD UP FACTOR; - ATTENUATION EQUIVALENT; - together with, as appropriate, an indication of homogeneity. Ways of stating values of ATTENUATION properties in compliance with this part of the International Standard are included. Excluded from the scope of this international standard are: - -Methods for periodical checks of PROTECTIVE DEVICES, particularly of PROTECTIVE CLOTHING, - methods of determining the ATTENUATION by layers in the RADIATION BEAM, and - methods of determining the ATTENUATION for purposes of protection against IONIZING 153 RADIATION provided by walls and other parts of an installation.