Understanding spark formation and growth in inert porous media and the implications for the response of low density PETN to electrostatic discharge initiation

Electrostatic energy is a constant threat to energetic materials and electro-explosive devices, such as detonators. However, the mechanism by which sparks interact with energetic materials to provoke detonation is not certain. As a first step to unravelling the spark initiation mechanism of low density PETN in exploding bridgewire detonators an integrated experimental and modelling study has been undertaken. To gain an understanding, spark formation and growth has been studied in air, inert porous beds and low density PETN. Spark initiation thresholds for PETN have been measured for two spark gap distances and compared to published data. Electrical models, incorporating the Braginskii equations, have been developed to enable spark energies and radii and the specific energy, Σ, to be estimated as a function of time. The energy thresholds have been calculated, by determining the conditions required for Σ to exceed the critical specific energy, Σc, which was derived from published PoP plot data. The calculated and experimental values are compared.