CHARACTERISTICS OF INCENDIVE AND NON-INCENDIVE SPARK DISCHARGES FROM THE SURFACE OF A CHARGED INSULATOR

Naturally occurring electrostatic discharges have been simulated to determine the possibilities of ignition initiation in an explosive open atmosphere by a discharge between a planar distribution of charge and an earthed electrode. The waveforms, patterns and paths of the discharges were monitored to reveal the intensity and the degree of discreteness of the discharges. Thresholds for both incendive and non-incendive sparks have been determined in terms of both the energy density of the surface discharge, and of the surface potential of the charged layer. The threshold energy density was found to vary with the charge density. The minimum energy density thresholds for incendive and non-incendive sparks were found to be 10 J/m2 and 0.25 J/m2, respectively. Threshold energy, the product of the threshold energy density and the surface area of the discharge, was found to be a far less reliable measurement. Values for threshold energy were found to be as low as 0.2 mJ for non-incendive sparks and 26 mJ for incendive sparks.