Three UK and seven US production formulations qualified as replacements for tetryl in fuzes have been obtained through TTCP WTP-1. Characterization of powders - Rotter impact sensitiveness, temperature of ignition, vacuum thermal stability and electrostatic spark sensitivity - and of pressed charges - shock sensitivity - has been carried out at MRL. The use of tetryl in munition filling operations has largely been phased out in Western countries. The US has ceased manufacture and filling with tetryl, and the UK is designing and filling all new stores with alternative explosives. The principal reason for these decisions has been the pollution and environmental problems associated with manufacture of tetryl, together with the possible associated health risks to personnel engaged in filling operations. Australia has never manufactured tetryl and stock held in storage was sufficient for requirements for a number of years at current usage rates. As a consequence, replacement of tetryl received low priority, but in 1985 MRL was tasked to investigate and recommend suitable materials.