Cloth masks inferior for protection against airborne viral spread
Simulations reveal low filtration efficiency in woven fabric

Date:
March 1, 2022
Source:
American Institute of Physics
Summary:
A new study examines the efficacy of particle filtration by woven
fabric, which consists of fibers twisted together into yarns. There
are, therefore, two lengthscales: the diameters of the fiber and
the yarn.

Using 3D imagery produced by confocal microscopy to see the air flow
channels, the scientists simulate the airflow through these channels
and calculate filtration efficiency for particles a micrometer and
larger in diameter. The study concludes for particles in this size
range, the filtration efficiency is low.



FULL STORY ==========================================================================
Like many other viruses, COVID-19 is transmitted primarily via particles carried in the air. An infected person breathes out particles containing
the virus into the air, which can then be inhaled by another person,
who then becomes infected.


========================================================================== Masks are widely considered an important first-line defense against
airborne transmission of the disease, as is supported by a preponderance
of evidence.

Fueled by the omicron variant, the latest wave of the pandemic prompted
public health officials to recommend more protective face coverings
because not all masks are created equal.

In Physics of Fluids, by AIP Publishing, researchers from England,
Germany, and Francefocus their expertise -- and their microscopes -- on examining the efficacy of particle filtration by woven fabric, which,
unlike material used in standard air filters and masks, consists of
fibers twisted together into yarns.

There are, therefore, two lengthscales: the diameters of the fiber and
the yarn.

Using 3D imagery produced by confocal microscopy to see the air flow
channels, the scientists simulate the airflow through these channels and calculate filtration efficiency for particles a micrometer and larger
in diameter. The study concludes for particles in this size range,
the filtration efficiency is low.

"Masks are air filters, and woven fabrics, such as cotton, make for good
jeans, shirts, and other apparel, but they are lousy air filters," said co-author Richard Sear, from the University of Surrey. "So, use woven
fabric for clothing, and N95s or FFP2s or KF94s for masks." Indeed,
the flow simulations suggest when a person breathes through cloth, most
of the air flows through the gaps between the yarns in the woven fabric, bringing with it with more than 90% of the particles.

"In other words, these relatively large gaps are responsible for cloth
being a bad material to make air filters from," said Sear. "In contrast,
the filtering layer of an N95 mask is made from much smaller, 5-micrometer fibers with gaps that are 10 times smaller, making it much better for
filtering nasty particles from the air, such as those containing virus."
While earlier research revealed similar findings, this study represents
the first to simulate particles going directly through the gaps in
woven fabric.

Sear added good masks should feature the "two Fs: good filtration and
good fit." "Surgical masks fit badly, so a lot of air goes unfiltered
past the edges of the mask by the cheeks and nose," said Sear.

The article "Modelling the filtration efficiency of a woven fabric:
The role of multiple lengthscales" is authored by Ioatzin Rios de Anda,
Jake W. Wilkins, Joshua F. Robinson, C. Patrick Royall, and Richard
P. Sear. The article will appear in Physics of Fluidson March 1, 2022.

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


========================================================================== Journal Reference:
1. Ioatzin Rios de Anda, Jake W. Wilkins, Joshua F. Robinson,
C. Patrick
Royall, Richard P. Sear. Modeling the filtration efficiency of a
woven fabric: The role of multiple lengthscales. Physics of Fluids,
2022; 34 (3): 033301 DOI: 10.1063/5.0074229 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220301131049.htm

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