Craniometric Determinants of the Fitted Filtration Efficiency of Disposable Masks

Introduction:     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 whether craniofacial morphology impacts the efficiency of disposable masks (N95, KN95, surgical masks, KF94) most often worn by the public to protect against toxic and infectious aerosols. This project was registered with ClinicaltTrials.gov (NCT05388201; registration May 18, 2022). Methods:     One-hundred participants (50 men, 50 women) visited the Environmental Protection Agency’s Human Studies Facility in Chapel Hill, NC between 2022-2023. Craniometrics and 3D scans were used to separate participants into four clusters. 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. Fitted filtration efficiency was quantified for each mask at baseline and when tightened using an ear-loop clip. Results:     The mean unmodified mask performance ranged from 55.3% (15.7%) in the large KF94 to 69.5% (12.3%) in the KN95. Modified performance ranged from 66.3% (9.4%) in the surgical to 80.7% (12.0%) in the KN95. Clusters with larger face width and neck circumference had higher unmodified mask efficiency. Larger nose gap area and nose length decreased modified mask performance. Discussion:     We identify face width, nose size, nose shape, neck circumference, and ear breadth as specific features that modulate disposable mask fit in both unmodified and modified conditions. This information can optimize guidance on respiratory protection afforded by disposable ear-loop masks.

Impact/Purpose

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. 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. Do all masks protect everyone equally? Peer-reviewed research article describing the role of craniofacial dimensions and characteristics in the fitted efficiency of different types of face coverings. Variation in facial morphology is known to contribute significantly to heterogeneity in the fitted efficiency of N95 respirators. However, virtually nothing is known about how facial dimensions affects the fit and performance of the types of face coverings worn by the public during the COVID-19 pandemic. This study will compare the fitted performance of different types of face coverings (N95, KF94, KN95, procedure) in a population of study volunteers whose craniofacial dimensions are measured using conventional and 3-D capture imaging. The findings will inform the public on the optimal type of face coverings for individuals with specific facial characteristics.    How well do masks keep infectious agents inside the mask? Peer-reviewed research article describing the fitted containment efficiency of face coverings of different types. Face coverings protect the wearer as well as others from the wearer. No quantitative methods currently exist for the assessment of the performance of face coverings worn as source control. The proposed project will develop and test a novel quantitative method for the evaluation of the efficiency of fitted face coverings of different types in preventing particles from escaping into the surrounding air. This method will be the first quantitative assessment of the source control function of masks on a breathing person (as opposed to a mannequin).  This information will be used to assess the efficacy of face coverings in combating the spread of respiratory infections in exposed populations.  How long can face disposable face masks be worn? Peer-reviewed journal article reporting on the durability of disposable face coverings subjected to extended wear.       When fitted properly, N95 respirators are highly effective in protecting the wearer against infections and toxic aerosols. There is very little information on the durability of the performance of respirators and other types of face covering. Disposal of masks has added to the global plastic waste disposal environmental problem. If it can be done safely, extending the useful life of disposable masks can reduce this burden significantly. This study will test the fitted filtration efficiency of different types of disposable face coverings (N95 respirators, KN95, KF94, procedure) that have been subjected to repeated wear, as well as face coverings that have been laundered. The findings of this study will inform approaches to the mitigation of  environmental costs associated with the manufacturing and disposal of disposable face coverings. 

Citation

Griffin, J., E. Mcinroe, E. Pennington, W. Steinhardt, H. Chen, S. Prince, AND J. Samet. Craniometric Determinants of the Fitted Filtration Efficiency of Disposable Masks. Frontiers, Lausanne, SWITZERLAND, 12:1444411, (2024). [DOI: 10.3389/fpubh.2024.1444411]

DOI: Craniometric Determinants of the Fitted Filtration Efficiency of Disposable Masks