Facial anthropometric dimensions distribution and effects to fits of filtering facepiece respirators in Chinese people
Authors: zhang Xueyan , xu Qing , Yang Mimi , Liu Xiaoxu , jia Ning , Wang Zhongxu , Sun Xin 
Published: October 2023

Abstract
Objective To identify the facial anthropometric dimensions distribution and influential factors to fits of filtering facepiece respirators (FFRs) in Chinese population.
Methods Measurement of 22 facial anthropometric dimensions and fit test were conducted among 785 subjects, who were health care workers and community population in Beijing. 3M 9132, Siwo D918(ear belt with a hook) Siwo D918(head belt) and Wenjian medical N95 respirator were used for the health care workers as well as 3M 9501+, 9502+ respirators were used for community population to do the fit test. The fit of FFRs were measured by a PortaCount fit tester. A fit factor of no less than 100 was considered as “pass” on the fit test. Passing rate (PR) of each FFR was determined as the percentage of the number of people passed the fit test to the number of people participated the fit test. For health care workers, no other FFRs would be tested once a fitted model had been selected by the fit test. Each community people tested no more than 2 FFRs for fit test whether the result pass or not. The PRs were compared by χ2 test. The t-test and ANOVA were used to compare the differences of facial anthropometric dimensions between different feature groups. Non-conditional logistic regression model was used to analyze the influential factor to the fit.
Results The morphological facial length-bizygomatic breadth distribution of 77.1% (605/785) subjects and 69.7% (547/785) were within the bounds of NIOSH and Chinese bivariate fit test panels respectively. The morphological facial length was different significantly by native place of subject (F=5.288, p<0.05) while the difference was not found in bizygomatic breadth (p>0.05). 949 fit tests were conducted totally. All health care workers had chosen one fit FFR at least of the four models available. The overall passing rate(PR) was 73.3% (696/949) with no significant gender difference could be observed (p>0.05). The PRs of the 6 FFRs were 49.1%, 90.8%, 81.2%, 9.5%, 17.6% and 59.0%, which were significantly different (p<0.05). Gender difference of PR was not significant of each FFR (p>0.05). There was a difference of PR among subjects with different native place (χ2=27.365, p<0.05). The PRs of different native place groups are 80.6% (Beijing), 71.8% (Shanxi), 70.7% (Hebei), 67.6% (Henan), 65.4% (other provinces) and 58.8% (Shandong). It was found that the effects of age, native place, bitragion-ophryon arc, bitragion-submandibular arc, head breadth and nasal height on fit of FFRs were significant (p＜0.05).
Conclusion The fit of a FFR is different significantly in different native populations. It is necessary to conduct fit test before the first using, especially for those with the high respiratory exposure risk. Facial anthropometric dimensions of individuals should be considered when designing and selecting a FFR, as dimensions has an impact on fit. It is better to supply several alternative models of FFR to ensure a satisfying level of fit in target population.