Craniometric Determinants of the Fitted Filtration Efficiency of the Most Commonly Worn Disposable Masks

Objective: To determine 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. 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. 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. Conclusions: 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

Given the relatively large impact of craniofacial dimension on ear-loop style mask performance   identified in this study, these findings provide a basis for improved guidance to the public during air quality emergencies. We identify overall head size, nose size, and ear breadth as specific features that modulate disposable mask fit in both unmodified and modified (clipped) conditions. Specifically, larger faces tend to provide a protective benefit by reducing gaps between the mask and the skin. However, there appears to be a ceiling above which craniofacial size can limit and in some cases impair mask performance. The limiting effect of face and head size was most apparent when modifying the mask with a clip as evident by nose size and shape, which are the most influential factors on whether an individual could achieve 80% or higher in a modified mask. One-size-fits-all does not mean that one size protects all equally. By defining and quantifying the human variation in craniofacial structure, this study identifies dimensions of the head and face that may lead to guidance for optimizing respiratory protection afforded by disposable ear-loop masks at an individualized level. We show that it is possible to predict the range of fitted performance based on reducing mis-sizing between the face and the mask both for an unmodified mask and when tightening the mask using an ear-loop clip. These findings show that considering the variation in craniofacial dimensions can lead to better public health guidance and optimize the protection that can be achieved with a disposable mask during air quality emergencies.

Citation

Griffin, J., E. Mcinroe, E. Pennington, W. Steinhardt, H. Chen, S. Prince, AND J. Samet. Craniometric Determinants of the Fitted Filtration Efficiency of the Most Commonly Worn Disposable Masks. American Association of Biological Anthropologists, Los Angeles, CA, March 19 - 23, 2024.