Effect of Dust Loading on the Performance of Half-Mask Respirators

Abstract

The effect of dust loading on the protection provided by an air purifying respirator is complicated because of the interplay of two factors: (1) the increase in filter resistance, with its attendant increase in facial seal leakage; and (2) the increase in filter efficiency that occurs with increased loading. The objective of this article is to characterize, based on experimental measurement, the effect of dust loading on the protection provided by three types of respirators: (1) dust and mist (DM, disposable); (2) dust, fume, and mist (DFM, dual cartridge); and (3) dust, fume, mist, and radionuclide (DFMR, dual cartridge). Respirator filters were loaded with AC Fine Test Dust (mass median aerodynamic diameter = 2.8 μm, geometric standard deviation = 2.9) to six successive loading conditions, approximately 0, 100, 200, 400, 800, and 1600 mg, using a breathing machine (work rate 68 W) and a dust chamber. At each loading condition penetration and resistance measurements were made at seven flow rates (2–150 L/min). Penetration was measured at 12 particle sizes (0.14–3.6 μm) with a PMS, Inc. LAS-X optical particle counter. The effect of changes in resistance and penetration on respirator performance was evaluated using a respirator performance predictive model. For DM and DFM respirators protection increased until a loading of 200 to 400 mg was reached and then decreased gradually. In situations where fit factors exceed 100, loading is beneficial in terms of protection factor for DM and DFM respirators, at least until more than 1 g of dust is collected on the filters. Loading decreases the protection provided by respirators using high efficiency (DFMR) filters. Under the usual conditions of use the change in protection factor due to loading is unlikely to exceed a factor of three.