Measurement of transferred charge in brush discharges from insulating materials

Safe practice requires that the use of insulators is avoided in hazardous areas containing potentially explosive atmospheres. However, in some processes, insulators are essential components and cannot be replaced by conducting materials. Evaluation of insulators for safe use in hazardous areas is discussed with particular reference to the requirements of international standards. Examples of testing by the measurement of transferred charge in brush discharges from insulating materials are presented, which indicate that using different size electrodes than specified in international standards can result in higher or lower measured transferred charge, and can, in some cases, lead to a different test outcome and evaluation of safety. The examples presented are from commercial testing and are included in this short communication to illustrate issues that the author has experienced when implementing international standards.