Face shape influences mask fit, suggests problems with double masking
against COVID-19
Proper fit crucial for optimal mask protection

Date:
May 3, 2022
Source:
American Institute of Physics
Summary:
In a new study, researchers used principal component analysis along
with fluid dynamics simulation models to show the crucial importance
of proper fit for all types of masks and how face shape influences
the most ideal fit. They modeled a moderate cough jet from a mouth
of an adult male wearing a cloth mask over the nose and mouth with
elastic bands wrapped around the ears and calculated the maximum
volume flow rates through the front of mask and peripheral gaps
at different material porosity levels.



FULL STORY ==========================================================================
In its updated guidance at the start of 2022, the U.S. Centers for
Disease Control and Prevention said loosely woven cloth masks offer
the least protection against COVID-19, and N95 and KN95 masks offer the
most protection.

Still, after more than two years since the pandemic began, there is
not a full understanding of mask characteristics for the most optimal protection.


==========================================================================
In Physics of Fluids, published by AIP Publishing, researchers at Florida
State University and Johns Hopkins University use principal component
analysis (PCA) along with fluid dynamics simulation models to show the
crucial importance of proper fit for all types of masks and how face
shape influences the most ideal fit.

The study suggests double masking with improperly fitted masks may
not significantly improve mask efficiency and produces a false sense
of security.

More layers mean a less porous face covering, leading to more flow forced
out of the perimeter gaps (sides, top, and bottom) in masks with a less
secure fit.

Double layers increase filtering efficiency only with good mask fit but
could also lead to breathing difficulties.

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

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

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

"Facial asymmetry is almost imperceivable to the eye but is made obvious
by the cough flow through the mask," said co-author Tomas Solano, from
Florida State University. "For this particular case, the only unfiltered leakage observed is through the top. However, for different face shapes, leakage through the bottom and sides of the mask is also possible."
Creating "designer masks" customized to each person's face is not
practical at scale. Still, PCA-based simulations can be used to design
better masks for different populations by revealing general differences
between male and female or child versus elderly facial structures and
the associated air flow through masks.


========================================================================== Story Source: Materials provided by American_Institute_of_Physics. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Tomas Solano, Chuanxin Ni, Rajat Mittal, Kourosh Shoele. Perimeter
leakage of face masks and its effect on the mask's efficacy. Physics
of Fluids, 2022; 34 (5): 051902 DOI: 10.1063/5.0086320 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/05/220503110525.htm

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