Fit test for filtering facepieces: search for a low-cost, quantitative method.
Conventional fit-testing methods use HEPA filter cartridges to distinguish face-seal leakage from filter penetration and thereby test a respirator's ability to face-seal. These methods cannot be applied to low-efficiency filtering facepieces that also protect the wearer through aerosol particle retention by the filter material. Therefore, the ability of a filtering facepiece to face-seal is of interest to the developer for improving the design and to the user for finding the conditions for optimal face-seal. A unique difference has been found between the combined aerosol penetration through filter medium and leak site at low versus high flow rate. This feature has been used to differentiate face-seal leakage from filter penetration. A "fit index" has been introduced as the most sensitive indicator of fit. When normalized by reference to the aerosol penetration through the filter material, this index displays a unified behavior irrespective of the filter material used. The fit index is determined by relating the measured total aerosol concentration at a high flow rate to that at a low flow rate. Tests during normal breathing of a human subject compare well with the data obtained during breath-holding experiments. Available instruments may be used for this test, but need to be modified for tests on humans.
Myojo
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Department of Environmental Health, University of Cincinnati, OH 45267-0056.
Willeke
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Chen
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D000336:Aerosols; D005374:Filtration / Q000295:instrumentation*; D006801:Humans; D010316:Particle Size; D012134:Respiratory Protective Devices
D000336:Aerosols