Industrial hygiene implications of the static electrification of workplace aerosols

Abstract

This paper reviews the electrostatic properties and effects of workplace aerosols as they relate to industrial hygiene. It summarises what is known about the nature of the charging of aerosols generated in industrial workplaces, the results of studies in workplaces together with those of relevant laboratory studies, the effects of aerosol charge on the deposition of inhaled particles in the respiratory tracts of humans and animals, the effects on aerosol sampling in the workplace, and the effects on filtration. The main conclusions are that: (a) workplace aerosols are invariably charged to levels substantially above Boltzmann equilibrium (with the distribution between positive and negative polarity usually being approximately symmetrical); (b) effective charging levels are higher for fibrous aerosols (e.g., asbestos) than for most similarly dispersed non-fibrous ones; (c) the effect of aerosol charge is to enhance deposition in the deep lung by the action of electrical image forces (d) the magnitude of deposition for most practical aerosols is insignificant for isometric particles but might not be for fibrous ones; (e) the effects on the aspiration efficiencies of aerosol samplers are small but the effects on particle transport through tubes, cowls, transition sections and onto the filters of samplers may be large; and (f) aerosol charge enhances the particle collection efficiencies of many air filters but, in the case of artificially electrified filters, causes a degradation in performance due to progressive charge neutralisation.