The best (and worst) materials for masks
People making homemade masks might want to reach for a vacuum cleaner
filter

Date:
July 8, 2020
Source:
University of Arizona
Summary:
It's intuitive and scientifically shown that wearing a face
covering can help reduce the spread of the novel coronavirus that
causes COVID-19. But not all masks are created equal, according
to new research.



FULL STORY ==========================================================================
It's intuitive and scientifically shown that wearing a face covering can
help reduce the spread of the novel coronavirus that causes COVID-19. But
not all masks are created equal, according to new University of
Arizona-led research.


========================================================================== Amanda Wilson, an environmental health sciences doctoral candidate in
the Department of Community, Environment and Policy in the Mel and Enid Zuckerman College of Public Health, is lead author on a recent study
published in the Journal of Hospital Infection that assessed the ability
of a variety of nontraditional mask materials to protect a person from infection after 30 seconds and after 20 minutes of exposure in a highly contaminated environment.

When the researchers compared wearing masks to wearing no protection
during 20- minute and 30-second exposures to the virus, they found
that infection risks were reduced by 24-94% or by 44-99% depending on
the mask and exposure duration. Risk reduction decreased as exposure
duration increased, they found.

"N99 masks, which are even more efficient at filtering airborne particles
than N95 masks, are obviously one of the best options for blocking
the virus, as they can reduce average risk by 94-99% for 20-minute
and 30-second exposures, but they can be hard to come by, and there
are ethical considerations such as leaving those available for medical professionals," Wilson said.

The next best options, according to the research, are N95 and surgical
masks and, perhaps surprisingly, vacuum cleaner filters, which can
be inserted into filter pockets in cloth masks. The vacuum filters
reduced infection risk by 83% for a 30-second exposure and 58% for a
20-minute exposure. Of the other nontraditional materials evaluated
by the researchers, tea towels, cotton-blend fabrics and antimicrobial pillowcases were the next best for protection.

Scarves, which reduced infection risk by 44% after 30 seconds and 24%
after 20 minutes, and similarly effective cotton t-shirts are only
slightly better than wearing no mask at all, they found.



==========================================================================
"We knew that masks work, but we wanted to know how well and compare
different materials' effects on health outcomes," said Wilson, who
specializes in quantitative microbial risk assessment.

Wilson and her team collected data from various studies of mask efficacy
and created a computer model to simulate infection risk, taking various
factors into consideration.

"One big component of risk is how long you're exposed. We compared risk
of infection at both 30 seconds and 20 minutes in a highly contaminated environment," she said.

Other conditions that impact risk of infection are the number of people
around you and their distance from you, she said.

The size of virus-transporting droplets from sneezes, coughs or even
speech is also a very important factor. Larger, heavier droplets carrying
the virus drop out of the air faster than smaller, lighter ones. That's
one reason distance helps reduce exposure.



========================================================================== "Aerosol size can also be affected by humidity," Wilson said. "If the air
is drier, then aerosols become smaller faster. If humidity is higher,
then aerosols will stay larger for a longer period of time, dropping
out faster.

That might sound good at first, but then those aerosols fall on surfaces,
and that object becomes another potential exposure route." The study
also showed that the more time a person spends in an environment where
the virus is present, the less effective a mask becomes.

"That doesn't mean take your mask off after 20 minutes," Wilson said,
"but it does mean that a mask can't reduce your risk to zero. Don't
go to a bar for four hours and think you're risk free because you're
wearing a mask. Stay home as much as possible, wash your hands often,
wear a mask when you're out and don't touch your face." Masks protect
the wearer and others in a number of different ways. Wilson said there
are two "intuitive ways" that masks filter larger aerosols: mechanical interception and inertial impaction.

"The denser the fibers of a material, the better it is at
filtering. That's why higher thread counts lead to higher
efficacy. There's just more to block the virus," she said. "But some
masks (such as those made from silk) also have electrostatic properties,
which can attract smaller particles and keep them from passing through
the mask as well." The model developed by Wilson and her colleagues
included parameters such as inhalation rate -- the volume of air inhaled
over time -- and virus concentration in the air.

"We took a lot of research data, put it into a mathematical model and
related those data points to each other," Wilson said. "For example, if
we know people's inhalation rates vary by this much and know this much
virus is in the air and these materials offer this much efficiency in
terms of filtration, what does that mean for infection risk? We provide a range, in part, because everyone is different, such as in how much air we breathe over time." Wilson also said it's important for a mask to have
a good seal that pinches at nose, and she noted that people shouldn't
wear a mask beneath the nose or tuck it under the chin when not in use.

"Proper use of masks is so important," Wilson said. "Also, we were
focusing on masks protecting the wearer, but they're most important to
protect others around you if you're infected. If you put less virus out
into the air, you're creating a less contaminated environment around
you. As our model shows, the amount of infectious virus you're exposed
to has a big impact on your infection risk and the potential for others'
masks to protect them as well."

========================================================================== Story Source: Materials provided by University_of_Arizona. Original
written by Mikayla Mace.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Amanda M. Wilson, Sarah E. Abney, Marco-Felipe King, Mark H. Weir,
Marti'n Lo'pez-Garci'a, Jonathan D. Sexton, Stephanie J. Dancer,
Jessica Proctor, Catherine J. Noakes, Kelly A. Reynolds. COVID-19
and non- traditional mask use: How do various materials compare in
reducing the infection risk for mask wearers? Journal of Hospital
Infection, 2020; DOI: 10.1016/j.jhin.2020.05.036 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200708125350.htm

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