Propagating brush discharge initiation of dust layers – A new test method

Abstract

In many powder handling processes, powder can be deposited onto a metal or conductive surface layers. If the powders are very good insulators, the deposited layer can build up electrostatic charges to the level of local electrostatic breakdown creating a propagating brush discharge. An explosion hazard can exist if the powder fines cling to the insulating layer in process. The occurrence of a discharge on the insulating layer, either by internal electrostatic breakdown or by moving a grounded object toward the insulating layer, can loft the dust into the air. This discharge may also have sufficient energy to ignite the dust cloud causing catastrophic explosion results. A new test method has been developed to simulate this occurrence. Its goal is to determine the electrostatic discharge energy in the propagating discharge required to ignite the lofted dust. Propagating brush discharge having energies less then 30 millijoules have ignited dust deposits on insulating surfaces backed up by grounded conductive material. A method description and some test results are presented in this paper.