Powder charging electrostatic discharges

Volume resistivity is a measure of the electrical resistance for a unit volume of material and is the primary criterion for classifying powders as low, moderate, or high insulating. Insulating powders have a propensity to retain electrostatic charge and can produce hazardous electrostatic discharges when exposed to grounded plant, equipment, or personnel. 

Although very unreactive in massive forms, the finely divided metal may be pyrophoric, a Japanese study of this hazard has been reported [1]. Consequent upon an explosion in a tantalum dust collector, further study of powder explosion was made. Minimum ignition energies were found to be much lower than previously supposed. An oxide coating makes it susceptible to electrostatic charge generaton and discharge [2]. See entry PYROPHORIC METALS (references 3,9)... 

Localized ionization (corona discharges) from sharp, grounded, conducting probes or wires can on occasions be used to reduce the level of electrostatic charge from powder particles entering a vessel. Electrostatic ionization devices are not, however, without problems, and should only be used after consulting expert advice. 

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