The ignition of primary explosives by electric discharges

Abstract

It has long been known that explosives can be ignited by electric sparks. Compounds such as lead styphnate are particularly sensitive, and electric discharges, arely visible to the naked eye, are capable of igniting them. This is a source of azard in the manufacture and handling of those primary explosives used as itiatory materials, and there is an extensive literature on methods of measurement and on experimental values of the minimum ignition energy of these materials Langevin & Bicquard 1934; Brown, Kusler & Gibson 1946; Morris 1947, 1953; Lathsburg & Schmitz 1949). A review of the literature followed by some experimental determinations, showed that widely varying values of ignition energy ould be obtained for the same substance by using different experimental test methods and conditions. A systematic investigation of this problem by Wyatt, Moore and Sumner at the Explosive Research and Development Establishment, Waltham Abbey, has revealed a number of factors which influence the ignition energy and this paper presents a brief summary of some aspects of their work. There are two types of test apparatus commonly used to measure the ease of ignition of initiator materials by electric sparks; first, a fixed-gap method in which e voltage is applied across two electrodes, one of which is covered by the material sted, the voltage being sufficient to break down the gap and cause a spark to ass; second, an approaching-electrode method in which the gap is initially too ide for a discharge to take place with the voltage applied, but a spark is produced moving one electrode towards the other. The energy dissipated in the discharge varied by changing the applied voltage or the capacity of the condenser used to ore the electrical energy.