Static electricity phenomena in the manufacture and handling of solid propellants

Abstract

Within the safety conditions improvement framework, SNPE has tried to evaluate the margins of safety in presence of static electricity. Various measurements, performed in the workshops, have highlighted the presence of static electricity during some operations. Significant electric charges were observed on inhibitors and packings material; it has been possible to record the electric potential accumulated on a core during the core pull out operation. The above potential may go up to several thousands of volts at the end of the pull out operation. Thus, SNPE has emplemented a large set of preventive operations which seem to be efficient such as, for instance, the use of graphit and systematic grounding of inhibitors. In the field of safety, preventive operations cannot provide an absolute warranty for any hazard. Therefore, in the event of electric charges generation, SNPE has tried to understand the behavior of propellants, and more particularly of composite propellants, with regard to electric discharges. The studies described herein show that capacitative discharges and constant potentials may ignite the combustion of composite propellants. The results analysis allowed SNPE to point out criteria based upon percolation phenomena and specific laws of volumic resistivity as a function of temperature. The above criteria should be able to predict - with a rather good approximation - the behavior of some propellants in regard to static electricity.