FIT TEST FOR FILTERING FACEPIECES - SEARCH FOR A LOW-COST, QUANTITATIVE METHOD

Conventional fit-testing methods use HEPA filter cartridges to disting uish face-seal leakage from filter penetration and thereby lest a resp irator's ability to face-seal. These methods cannot be applied to low- efficiency filtering facepieces that also protect the wearer through a erosol particle retention by the filter material. Therefore, the abili ty of a filtering facepiece to face-seal is of interest to the develop er 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 lo w versus high flow rate. This feature has been used to differentiate f ace-seal leakage from filter penetration. A ''fit index'' has been int roduced as the most sensitive indicator of fit. When normalized by ref erence to the aerosol penetration through the filter material, this in dex displays a unified behavior irrespective of the filter material us ed. 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 d uring normal breathing of a human subject compare well with the data o btained during breath-holding experiments. Available instruments may b e used for this test, but need to be modified for tests on humans.