Aerosol filtration and faceseal leakage characteristics of filtering facepieces

This study describes an aerosol generator and a sampling train which have been developed for filter and respirator-fit testing. The filtering facepieces and cartridges of nuisance dust, dust-mist, dust-mist-fume and HEPA respirators were tested. The penetration of aerosols through two types of surgical masks has been examined as well.; Most filtering facepieces used today are made of electret material. However, the removal by electrical forces is reduced in time, as aerosols deposit on the filter fibers. The contribution of this electrical removal and its change in time as a function of aerosol loading were investigated. This study also focuses on the effect of leak shape and filter resistance.; Aerosol penetration as a function of particle size differs considerably among certified respirators of the same category. The quality factor of one respirator may be as much as 6.6 times more than that of another respirator of the same category. The best dust-mist respirator tested may provide five times more protection than the worst dust-mist respirator. The surgical masks may be adequate to protect the patients from bacteria exhaled or expelled by the health care workers, but may not be sufficient for protecting the latter from submicrometer-sized airborne or aerosolized blood-borne pathogens.; The dust-mist filtering facepieces tested have similar fiber diameters and packing densities. At a face velocity of 10 cm/s and an aerosol size of 0.16 {dollar}mu{dollar}m, electrical force removal accounts for 69% of the total filtration for the respirator found to have the best filter quality but only 25% for the respirator found to have the worst filter quality.; A slit-like leak and multiple circular leaks penetrate less aerosol particles than a single circular leak of equal cross-sectional area. Thus, aerosol penetration through a leak is not governed by the cross-sectional area of the leak, but by the flowrate which decreases with increase in leak shape complexity. If there is substantial lack of faceseal fit and the breathing rate is low, a HEPA respirator may provide less protection than a dust-mist respirator, because the pressure drop is considerably higher for a HEPA respirator which pulls in more aerosols through the leak. (Abstract shortened with permission of author.)...