Characterization of methods for surface charge removal for the reduction of electrostatic discharge events in explosive environments

Electrostatic discharge (ESD) from charged dielectric materials used within explosive environments presents a significant hazard. To investigate dielectric surface charging, and methods of removing the charge, in detail and in a controlled way, a test stand has been built and utilized to study the behavior of several common dielectric materials used in such environments. A corona discharge source of the type used in electrostatic printing technology has been employed at normal laboratory temperatures and at low and high relative humidity in a controlled manner. Materials tested included black Kapton, yellow Kapton, Lexan, Delrin, and Adiprene with surface potentials (Vdiel) ranging from -1 kV to -15 kV. Uniform charging and discharging of individual dielectric samples of varying thickness has been observed, as characterized by spatial scans of the surface potential at low voltages such as -1 kV to -4 kV. At higher charging voltages, the surface potential is found to decay or increase with time in complex ways, showing a dependence on the magnitude of the surface potential (Vdiel), as well as two characteristic time constants d (τ1, τ2) in some cases. The initial decay of Vdiel (d) is rapid, while the subsequent decay of surface potential is much slower. The decay time constant(s) is(are) found to be a nonlinear function of the surface voltage, Vdiel. A conductive brush with a static dissipative handle, grounded to a metal backing plate proved the most effective method to remove surface charge (QS). Typically, 80-90% of QS could be removed, with a lower bound on the “discharged” surface voltage of -500 to -1000 V. Additionally, it was found that localized discharging results in an approximately constant electric field gradient, ∇E on the dielectric samples in 2D. Detailed experimental results, including the effects of humidity and temperature are presented.