3. New results, findings and trends
3.1. Incendivity of discharges
The characterisation of the incendivity of discharges is one of the most crucial points in an electrostatic hazard assessment. Such a characterisation is however, very complex. The formation and course of a discharge have to be related to the ignition process of an explosive atmosphere. A pragmatic approach is to perform real ignition tests. The discharge is generated and exposed to an explosive atmosphere of known minimum ignition energy(MIE). Based on such experiments the so-called equivalent energy—which equals the maximum MIE of the explosive atmosphere, which still can be ignited with this discharge—is attributed to the discharge [3] . Such tests are always necessary to validate any other procedure, they are however rather time consuming and require experience in the handling of explosive atmospheres.
One method, which is used more and more to characterise the incendivity of discharges, is the measurement of charge transfer. Von Pidoll has enhanced and validated this method particularly for the assessment of the incendivity of brush discharges in the presence of explosive atmospheres of explosion groups IIA, IIB and IIC [4]. Similar results for dust clouds are to date only partially available (see next
paragraph).
In the context of the incendivity characterisation of discharges by a comparison of the equivalent energy of discharges with the MIE of an explosive mixture, contradictory statements and inconsistent results lead to an ongoing debate among expert. Although the equivalent energy of brush discharges, determined with gases and vapours, lies at a few millijoules, even very sensitive dusts with a MIE at or below 1 mJ could not be ignited. This statement is strongly supported by very recent results [5]. From a scientific point of view the answer lies in the complexity of the problem mentioned above. The ignition process is not only governed by the total energy integrated over space and time, but also by the spatial power distribution.