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

This paper compares experimental measurements of filter performance wi th predictions of aerosol collection by dust-mist respirators using th e single fibre efficiency model and an empirical model developed by th e authors. The former, a theoretically-based semi-empirical model, ind icates that mechanical phenomena such as impaction, interception and d iffusion are responsible for only a fraction of the collection efficie ncy 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 a ttributed to electrostatic forces. Because it was not possible to dete rmine filter fibre charge the single fibre efficiency model could not be used to predict electrostatic collection. An empirical model develo ped from experimental data with monodisperse latex aerosols was used t o predict silica and asbestos collection. The empirical model adequate ly described silica collection, but predicted much higher asbestos pen etration than was observed experimentally.