This document specifies a method for the determination of the relative loss of mass which a metallic powder undergoes when heated in a stream of pure dry hydrogen under specified conditions. The purpose of this test is to evaluate a chemical powder characteristic which is of importance to the powder metallurgical industry. The test is not intended as a means for the determination of the content of specific elements. (See Annex A and ISO 4491-1.) The test method is applicable to unalloyed, partially alloyed and completely alloyed powders of the metals listed in table 1 (see 6.1). It is not applicable to lubricated powders or to mixtures of metal powders. The results can be influenced by the presence of reducible, oxidizable or volatile metals, metalloids or compounds (see Annex A). The results obtained on such powders shall be used with caution and their interpretation shall be subject to agreement between supplier and user.