Ignition hazard due to static electricity in particulate processes

Abstract

The paper gives a review of the state of the art in the field of powder ignition by discharges due to static electricity. After a short introduction, emphasis is given to most recent results from research on powder ignition by different types of discharges occurring during powder handling and processing. It is explained why minor changes of the equipment or of the particulate processes have a huge effect on the energy of spark discharges and thus on the ignition hazard. Discharges associated with charge accumulation on high resistivity powders and granules and on insulating walls of equipment are discussed, and the most recent results concerning their incendivity are reviewed. In this context, cone discharges, brush discharges, propagating brush discharges and corona discharges are dealt with. An assessment of the ignition hazard due to the build up of static electricity cannot occur without taking into account the relevant parameters characterizing the initiation and the course of dust explosions. The progress achieved in this field (measurement and interpretation of minimum ignition energy data, role of bulk resistivity, presence of flammable gases or vapours—so called hybrid mixtures, etc.) is also shortly reviewed.