ELECTROSTATIC DISCHARGE IGNITION OF ENERGETIC MATERIALS

Electrostatic discharge (ESD) ignition of explosives, pyrotechnics, or propellants is often considered to be mainly dependent upon various p hysical characteristics of the energetic material. This work shows tha t ESD ignition of secondary explosives tested in powdered form is prim arily dependent upon the chemical characteristics of the energetic mat erial (i.e., the decomposition rate kinetics of the materials). We pro pose that ignition occurs when a spark raises the temperature of the e xplosive particles to the point where thermal runaway occurs. ESD sens itivities of a diverse series of explosives were measured using a trav eling needle test apparatus with the powders slightly confined by Myla r tape to prevent formation and ignition of a dust cloud. Using global thermal decomposition rate coefficient expressions, two parameters we re calculated for each explosive: (1) the critical temperatures accord ing to the Frank-Kamenetskii formula for 20 mu m particles of each exp losive and (2) the temperatures at which the rate coefficient equaled 10(3) s(-1). These two sets of data were correlated with the observed ESD sensitivities for 50 percent probability of ignition, E-50. Excell ent correlations resulted, indicating that for ESD ignition under thes e conditions the spark discharge is primarily a thermal source.