The penetration of dust through porous foam filter media

Experiments have been carried out to investigate dust particle penetration through filters made up of porous plastic foam media. For particles close to respirable size, two main mechanisms of particle collection were identified, inertial impaction and gravitational deposition. These mechanisms compete in such a way that, over a substantial range of face air velocity, an increase in penetration due to a fall in one of them is offset by a decrease due to a rise in the other.

These characteristics were employed in developing a prefilter for a sampling respirator. This prefilter allows the selective penetration of dust according to the MRC/Johannesburg curve, independently of the breathing rate of the wearer. The sampling respirator is for use in assessing the effect of breathing rate on the actual respirable dust intakes of individual coal miners.