The use of finite element field analysis in investigating industrial electrostatic hazards

Large vessels containing electrostatically charged flammable mists or dust clouds form part of many industrial processes. Consequently, high internal space potentials and electric fields are possible, promoting electrostatic discharges. The risk of ignition is often addressed by nitrogen inertion or by adding explosion protection systems. A preferred cost-effective alternative is to analyse the process with the aim of determining the maximum electric field that can be generated inside the vessel, for comparison with breakdown strength of air at which electrostatic discharges can occur. This field can seldom be measured directly. It can, however, be determined by performing simple measurements of the charge concentration and vessel dimensions to model the electrostatic conditions using a finite element, field analysis package. The package has been routinely used in hazard analyses by Wolfson Electrostatics, allowing the potential distributions and electric fields inside vessels to be displayed, using interactive graphics, as contour lines, vectors or graphs. Two hazard investigations in which the package was used are described in this paper