Face shape influences mask fit, suggests double masking issues against COVID-19

Time course of cough when wearing a face mask. Credit: Tomas Solano

In its updated guidance in early 2022, the US Centers for Disease Control and Prevention said loosely-woven fabric masks offer the least protection against COVID-19, and N95 and KN95 masks offer the least protection against COVID-19. the most protection. Yet, after more than two years since the start of the pandemic, there is not a full understanding of the characteristics of masks for the most optimal protection.

In Fluid Physicsresearchers from Florida State University and Johns Hopkins University are using principal component analysis (PCA) along with computational fluid dynamics models to show the critical importance of proper fit for all types of masks and how face shape influences the most ideal fit.

The study suggests that double masking with ill-fitting masks may not significantly improve mask effectiveness and produces a false sense of security.

More layers mean a less porous face covering, resulting in more forced flow out of perimeter spaces (sides, top and bottom) in masks with a less secure fit. Double layers only increase filtering efficiency with proper mask fit, but can also lead to breathing difficulties.

The researchers modeled a moderate cough spray from the mouth of an adult male wearing a cloth mask over his nose and mouth with elastic bands wrapped around his ears. They calculated the maximum volume flow rates through the front of the mask and the peripheral spaces at different levels of material porosity.

For a more realistic 3D face shape and size, the researchers used PCA which integrated 100 adult male heads and 100 adult female heads extracted from head analysis data at the University of Basel in Swiss. PCA condenses large sets of variables while retaining most of the information.

Their model showed how the slight asymmetry typical of all facial structures can affect the proper fit of the mask. For example, a mask may have a tighter fit on the left side of the face than on the right side.

“The facial asymmetry is almost imperceptible to the eye but is made evident by the cough flow through the mask,” said co-author Tomas Solano, from Florida State University. “For this particular case, the only observed unfiltered leakage is from the top. However, for different face shapes, leakage from the bottom and sides of the mask is also possible.”

Creating personalized “designer masks” for each person’s face is impractical on a large scale. Yet, PCA-based simulations can be used to design better masks for different populations by revealing general differences between male and female facial structures or children versus older people and the associated airflow through the masks.

Face masks block exhaled particles, despite edge leakage

More information:
Perimeter leaks of face masks and their effect on mask effectiveness, Fluid Physics (2022). aip.scitation.org/doi/10.1063/5.0086320

Provided by the American Institute of Physics

Quote: Face shape influences mask fit, suggests dual masking issues against COVID-19 (2022, May 3) Retrieved May 4, 2022 from https://phys.org/news/2022-05-mask -problems-masking-covid-. html

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