A rescue device which attaches to the frame of a self-contained breathing apparatus carried on the back of emergency workers such as firemen, hazardous-waste cleanup crews, and other individuals entering into hostile environments. For this, an expanded digital signature is created which, in addition to the hash, contains other information, in particular information identifying the hardware and software environment used in generating the signature. In one example, a friction stir weld tool includes tungsten and rhenium and is characterized by carbide and oxide dispersoids, by carbide particulates, and by grains that comprise a solid solution of the tungsten and rhenium.