Abstract
Xβray studies have been made of the detonation of cartridges of various explosives that had been compressed and reduced in diameter and then fired with a delay detonator. In several cases the detonation wave that travelled along the cartridge in a direction opposite to that in which the detonator was pointing, i.e. the retrograde detonation wave, appeared to die out completely. This was not observed in similar studies with cartridges of normal densities and diameters. It is suggested that the possibility of fading of the retrograde detonation wave is connected with the way the explosive compacts under pressure, this compaction being influenced by the nature of the crystalline components of the explosive.
The study suggests one mechanism by which undetonated explosive might be left following delay round shotfiring in coal; earlier shots, causing desensitisation and consequent failure of the retrograde detonation wave. If failure of the retrograde detonation wave occurred, appreciable quantities of undetonated explosive could remain which on becoming mixed with neighbouring coal dust might be capable of deflagrating, even at atmospheric pressure.