Factors Affecting the Location and Shape of Face Seal Leak Sites on Half-Mask Respirators

Abstract

While there have been a number of studies on the effect of leak site and shape on the magnitude of measured leakage through respirator face seals, there have been very few studies to identify the location and size of these leaks. In a previous study we used a method of identifying the location and shape of respirator leaks on a half-mask respirator by the deposition of a fluorescent tracer during a fit test, and testing for their association with facial dimensions. The purpose of this study was to apply that methodology to conduct multiple fit tests to determine if gender, respirator brand, repeated fit tests, and test exercises affected the location and shape of face seal leak sites. Categorical analysis found that none of these factors had a significant effect on the location and shape of leaks. General linear model analysis found some significant effects of the study factors on leaks, but facial dimensions had a greater effect, and there were significant differences between facial dimensions of subjects with a leak and those without. Significant differences in leak site distributions between this and the previous study may have been due to differences in facial dimensions and racial/ethnic composition. Twice as many diffuse leaks as point leaks were observed in both studies, indicating that slit-like leaks would be most appropriate on mannequins used in laboratory respirator leakage studies, and in respirator flow and penetration models. That the study factors had no significant effects in the categorical analysis, significant effects for facial dimensions were found in the linear analysis, and leak site distribution differences between this and our previous study may have been affected by differences in facial dimensions, indicate that, in addition to size, the shape of an individual's face may be an important determinant of leak sites on a half-mask respirator. This would have implications for the design of respirator facepieces and in the selection of respirators for individual wearers.

Keywords:

• aerosol
• anthropometry
• facial dimensions
• fit test
• fluorescent tracer
• gender

ACKNOWLEDGMENTS

The authors acknowledge funding support from NIOSH Grant 1K01OH00085.

The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of the National Institute for Occupational Safety and Health.

Notes

*Significant difference between genders.

^A The number of shape observations exceeds the number of tests because some tests resulted in multiple leaks.

^A Logistic regression using facial dimensions with significant parameter estimates as independent variables in the model.