The measurement of electric charge on airborne dusts in quarries and mines.

The distribution of charge on airborne dusts was measured in two quarries and a coal mine. An optical particle counter was used for the measurements in the quarries. For the mine, an alternative measurement system was developed, in which the particles were collected on elutriator plates for subsequent assessment by electron microscopy. The airborne dusts were at charge levels substantially above Boltzmann equilibrium, and with approximately symmetrical distributions between positive and negative polarity. The median magnitude of charge per particle increased with particle size. The median charge levels at these locations were not high enough to have substantial influence on the deposition of these dusts in lungs when inhaled. There was variation in the charge level due either to the differences in dust making processes or to the ageing of the aerosol. (orig./PW).