Electrostatic discharge (ESD) ignition of explosives, pyrotechnics, or propellants is often considered to be mainly dependent upon various physical characteristics of the energetic material. This work shows that ESD ignition of secondary explosives tested in powdered form is primarily dependent upon the chemical characteristics of the energetic material (i.e., the decomposition rate kinetics of the materials). We propose that ignition occurs when a spark raises the temperature of the explosive particles to the point where thermal runaway occurs. ESD sensitivities of a diverse series of explosives were measured using a traveling needle test apparatus with the powders slightly confined by Mylar tape to prevent formation and ignition of a dust cloud. Using global thermal decomposition rate coefficient expressions, two parameters were calculated for each explosive: (1) the critical temperatures according to the Frank-Kamenetskii formula for 20 mu m particles of each explosive 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. Excellent correlations resulted, indicating that for ESD ignition under these conditions the spark discharge is primarily a thermal source.