AN EMPIRICAL-MODEL FOR ESTIMATING THE COLLECTION EFFICIENCY OF DUST-MIST RESPIRATORS

This paper compares experimental measurements of filter performance with predictions of aerosol collection by dust-mist respirators using the single fibre efficiency model and an empirical model developed by the authors. The former, a theoretically-based semi-empirical model, indicates that mechanical phenomena such as impaction, interception and diffusion are responsible for only a fraction of the collection efficiency of dust-mist respirators, i.e. 30-70% depending on particle size. The difference between these relatively low predicted efficiencies and experimentally observed values, which were greater than 95%, can be attributed to electrostatic forces. Because it was not possible to determine filter fibre charge the single fibre efficiency model could not be used to predict electrostatic collection. An empirical model developed from experimental data with monodisperse latex aerosols was used to predict silica and asbestos collection. The empirical model adequately described silica collection, but predicted much higher asbestos penetration than was observed experimentally.