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Performance Evaluation of DM and DFM Filter Respirators—WORKING DRAFT 9.15.92

  A more sophisticated model developed by NIOSH is based on a relationship for filter and face-seal leakage that was first presented by Williams in 1980 and published in 1983.[1][2] This model was also given in 1984 by Campbell.[3] The derivation given in this evaluation for the improved model is based on that given by Campbell. This leakage-function model relies on the following assumptions:

e Pressure variations are sufficiently small such that the contaminated and filtered air can be considered incompressible.

® The cyclic performance of the respirator can be characterized by a representa- tive constant volumetric flow rate.

® During each inhalation cycle, the inhaled concentration Cinnaled Teaches equi- librium sufficiently quick so that it can be considered a constant during the entire inhalation cycle.

e The workplace concentration C, is spatially uniform and time independent.

e The contaminant concentration passing through the face seal Chace cont CQUals the workplace contaminant concentration C, (i.e., face-seal leakage Ltace seat = 1.00).

Start by considering a negative-pressure filter mask worn in a workplace contami- nant concentration C,. The contaminant concentration C,,,,,,4 in the volumetric air flow Qinhaid inhaled by the mask wearer is an air-flow-rate-weighted mixture of the contaminant concentration C,,,,, in the volumetric air flow Qhuer Penetrating the filter and the concentration C;,.. ..,; in the volumetric air flow Qhace ai that has breached the face seal-to-skin interface. Qi,,ce: is the sum of Qptuer 204d Qhnce sani

Then define the PF, as

  1. ↑ Williams, F.T.: An Analytical Method for Respirator Performance Prediction Utilizing the Quantitative Fit Test (QNFT), presented at NIOSH First International Respirator Research Workshop, Morgantown, West Virginia (September 11, 1980).
  2. ↑ Williams, F.T.: An Analytical Method for Respirator Performance Prediction Utilizing the Quantitative Fit Test, J. Int. Soc. Reap. Prot. 1(3):109-125 (1983).
  3. ↑ Campbell, D. L.: The Theoretical Effect of Filter Resistance and Filter Penstration on Respirator Protection Factors, J. Int. Soc. Resp. Prot. 2(3):198-204 (1984).
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