Determining the incendivity of electrostatic discharges without explosive gas mixtures

An analysis of the dependence of the minimum ignition energy (MIE) of a given explosive atmosphere on voltage and capacitance has shown that the charge Q transferred by a spark is a more suitable criterion than the MIE to describe its incendivity because it much less depends on voltage and gap width. Tables are presented which allow the determination of the minimum transferred charge Q_min necessary to achieve spark ignition for a number of different explosive atmospheres. It was found that the values for spark discharges are identical with the values for brush discharges determined up to now. In the case of single brush or spark discharges, Q can be easily obtained by charging a product as highly as possible in dry climate. Then, a discharge to a ball electrode connected to the input of a coulombmeter is provoked. After removal of the electrode from the remaining electric field the displayed value is read and compared with the threshold value for Q. In the case of multiple discharges, e.g., from high-voltage electrodes or textile materials, a high-frequency shunt resistance connected to a rapid oscilloscope is placed in the earth line of the ball electrode and the value for Q=∫Idt is read. Oscilloscopic records of current curves of corona, brush, and spark discharges are presented and discussed. Due to energy cumulation processes the proposed method needs further investigation to be suitable for determining the incendivity of permanent electric arc discharges.