EFFECT OF LEAK LOCATION ON MEASURED RESPIRATOR FIT

A significant difference in leak detection as a function of leak locat ion was observed during a study assessing how well current models of q uantitative fit-test systems detect leakage. Known sources of leakage (matched hypodermic needles) were introduced at three fixed locations into factory-probed half-mask and full-face respirators mounted on a h eadform-breathing machine system. The leak locations were the bridge o f the nose, the cheek, and the chin. Baseline leakage into each respir ator was determined by conducting a fit-rest with ail fixed leak sourc es capped. Fit tests were repeated with each individual source uncappe d. Study objectives included determining (1) how well each system meas ured the leakage, and (2) whether leak location had any effect on leak measurement. An ambient aerosol fit-rest system (Portacount Plus) and a controlled negative pressure (CNP) fit-lest system (FitTester 3000) were used. The ambient aerosol system detected an overall average of 37.2% of the known leakage, with a coefficient of variation of 44.7%. An analysis of variance showed significant differences in aerosol syst em measurements of leakage as a function of leak location and mask typ e (p < 0.0O1). A different pattern of aerosol leak detection as a func tion of leak location was observed between half-mask and full-face res pirators, which appears to be related to differences in in-mask airflo w dynamics. The CNP system detected an overall average of 97.9% of the known leakage through the same hypodermic needles, with a coefficient of variation of 4.3%. CNP system results were not affected by leak lo cation (p > 0.43) or mask type (p > 0.32).