Abstract
A novel method for measuring the fit factor of filtering face-piece respirators is described. Measurement is made by the continual monitoring of the pressure produced by a volume of air injected into the respirator cavity, and withdrawn so that the added volume varies sinusoidally with time. Sets of measurements, each corresponding to a single breath, can be made. Data analysis, in which these pressure measurements are compared with a reference wave from the device producing the volume change, enables a measurement of pressure wave amplitude to be made for individual breaths. Comparison between measurements made when leaks occur and measurements made without leakage enables a fit factor to be calculated for each breath. Results obtained by the use of this method on a filtering facepiece worn by a manikin are compared with bubble flowmeter measurements and shown to agree (correlation coefficients>0.98), though systematic differences exist. The method is most accurate when leakage is large, and is potentially useful for fit factors up to about 50, and leakages down to about 2%.