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The theoretical effect of filter resistance and filter penetration on respirator protection factors.

Campbell DL
J Int Soc Respir Prot 1984 Apr; 2(2):198-204
A mathematical model for predicting the effect of changes in filter resistance and filter penetration on the performance of negative pressure aerosol respirators was described. The model described the inhaled volumetric flow rate in the respirator as originating from two sources, flow through the filter and flow through the face seal leak. The inhaled aerosol concentration was treated as a mixture of the aerosol concentration passing through the filter and the concentration entering through the leak. It was assumed that for a specified aerosol challenge concentration, the concentration was homogeneous both in time and space and its equilibrium concentration was attained rapidly in each inhalation cycle; that the cyclic performance of the respirator could be treated as a constant flowrate; that the inhaled fluid was incompressible; and that the aerosol concentration passing through the face seal was equal to the challenge concentration. This led to equations that expressed the respirator protection factor as a function of filter resistance and filter penetration. Possible applications of the equations were listed. These included predicting how the protection factor of a particular respirator could be affected by simultaneous changes in filter resistance and filter penetration, how initial inhalation resistance affects overall respirator performance, and how the distribution of protection factors measured on a group of individuals are altered by changing filter penetration and filter resistance.
Mathematical-models; Respiratory-protective-equipment; Occupational-health; Air-filters; Air-flow; Air-pressure; Equipment-reliability; Health-protection
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Journal Article
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Journal of the International Society for Respiratory Protection
Page last reviewed: February 11, 2022
Content source: National Institute for Occupational Safety and Health Education and Information Division