Craniofacial morphology as a determinant of disposable respiratory protection fitted filtration efficiency
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Exposure to harmful aerosols is of increasing public health concern due to the SARS-CoV-2 pandemic and wildland fires. These events have prompted risk reduction behaviors, notably the use of disposable respiratory protection. This project investigated the role of craniofacial morphology as a determinant of the fitted filtration efficiency of commonly available face coverings (KN95, surgical masks, large KF94, medium KF94) in 100 participants (50 male, 50 female) between the ages of 18-55. Eighteen craniofacial measurements were collected using anthropological techniques and a 3D scan (Bellus3D Arc). Participants performed the modified quantitative Occupation Safety and Health Administration respirator fit testing procedure in a chamber supplemented with aerosolized sodium chloride particles. Each face covering was tested with and without an ear loop clip attached behind the head. Boosting and elastic net regression yielded five measurements (bizygomatic breadth, nose length, bizygomatic nasal arc, neck circumference, ear breadth) that were the best predictors of filtration efficiency based on overall model fit. Four groups with similar craniofacial dimensions were identified using k-means clustering. Participants in the group containing the smallest craniofacial dimensions (N=24) exhibited the lowest filtration efficiencies (KN95=62.3(2.4)%, surgical=48.8(1.6)%, large KF94=42.4(2.4)%, medium KF94=60.9(3.1)%) but averaged improvements of 17.5% when using a clip. In comparison, the best performing cluster (N=13) had efficiencies of: KN95=74.5(3.7)%, surgical=64.3(2.5)%, large KF94=67.1(4.0)%, medium KF94=73.6(5.1)% with an average clipped improvement of 7.4%. Overall, our results show that craniofacial morphology is a major determinant of fitted mask performance and should be considered when selecting disposable respiratory protection against exposures to harmful aerosols.