Faceseal leaks on one brand of half-mask respirator worn by 73 human subjects were identified by deposition of a fluorescent tracer aerosol during a standard quantitative fit test. The identified leaks were categorized according to their location and shape. It was found that about 89% of all observed leaks occurred at the nose or chin or were multiple leaks which included these sites. Fit factors for these types of leaks were significantly lower than for other types of leaks. About 73% of all leaks approximated the shape of a slit rather than a round orifice, and the prevalence of these leaks was affected by gender. Significant association of facial dimensions and leak sites were found. Most of these were attributed to differences in gender, and only a very small percentage were for the facial dimensions used to define the Los Alamos respirator test panel. Significant correlation of facial dimensions and fit factor were found for only three facial dimensions; none of which are used to define the test panel. Evidence of airflow streamlining within the facepiece was observed on 22% of the subjects. Results of this study indicate that respirator leakage is strongly affected by nose and chin leaks, that gender is a factor in how a respirator fits, and that consideration should be given to including nasal dimensions when defining a respirator test panel and selecting a respirator for an individual wearer.

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.

This study examined the association of facial dimensions with respirator fit considering the effect of gender and respirator brand. Forty-one subjects (20 white females and 21 white males) participated in the study. Each subject was measured for 12 facial dimensions using anthropometric sliding and spreading calipers and a steel measuring tape. Three quantitative fit tests were conducted with the same subject wearing one size of three different brands of half-mask respirators resulting in a total of nine fit tests. Linear mixed model analysis was used to model respirator fit as a function of gender and respirator brand while controlling for facial dimensions. Results indicated that the gender by respirator brand interaction was not statistically significant (p = 0.794), and there was no significant difference in respirator fit between males and females (p = 0.356). There was a significant difference in respirator fit among respirator brands (p < 0.001). Because correlations between facial dimensions and respirator fit differed across gender and respirator brand, six separate linear mixed models were fit to assess which facial dimensions most strongly relate to respirator fit using a "one variable at a step" backward elimination procedure. None of the 12 facial dimensions were significantly associated with respirator fit in all six models. However, bigonial breadth and menton-nasion length were significantly associated with respirator fit in five of the six models, and biectoorbitale breadth, bizygomatic breadth, and lip width were significantly associated with respirator fit in four of the six models. Although this study resulted in significant findings related to the correlation of respirator fit with menton-nasion length and lip width (the dimensions currently used to define the half-mask respirator test panel), other facial dimensions were also shown to be significantly associated with respirator fit. Based on these findings and findings from previous studies, it is suggested that other facial dimensions including bigonial breadth, biectoorbitale breadth, and bizygomatic breadth be considered when designing half-mask respirators, and that face length and lip width alone may not be appropriate in defining test groups whose fit is intended to be representative of worker populations.

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This study was designed to determine if three-dimensional (3D) laser scanning techniques could be used to collect accurate anthropometric measurements, compared with traditional methods. The use of an alternative 3D method would allow for quick collection of data that could be used to change the parameters used for facepiece design, improving fit and protection for a wider variety of faces. In our study, 10 facial dimensions were collected using both the traditional calipers and tape method and a Konica-Minolta Vivid9i laser scanner. Scans were combined using RapidForm XOR software to create a single complete facial geometry of the subject as a triangulated surface with an associated texture image from which to obtain measurements. A paired t-test was performed on subject means in each measurement by method. Nine subjects were used in this study: five males (one African-American and four Caucasian females) and four females displaying a range of facial dimensions. Five measurements showed significant differences (p<0.05), with most accounted for by subject movements or amended by scanning technique modifications. Laser scanning measurements showed high precision and accuracy when compared with traditional methods. Significant differences found can be very small changes in measurements and are unlikely to present a practical difference. The laser scanning technique demonstrated reliable and quick anthropometric data collection for use in future projects in redesigning respirators.