see url:
https://nypost.com/2020/08/09/scientists-tested-14-types-of-masks-in-preventing-spread-of-covid-19/
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Bandannas, gaiters and knitted masks are some of the least effective
face coverings for preventing the spread of coronavirus, according to a
new study.
Researchers at Duke University made the discovery while testing 14
different types of masks, according to the study published Friday.
N95 masks, often used by health care professionals, worked best to stop
the transmission of respiratory droplets during regular speech.
Other good performers at stopping leakage were three-layer surgical
masks and cotton masks, which can be made at home, the researchers with
Duke’s physics department found.
But while bandannas and knitted face coverings may be a unique look,
they did not offer much protection, according to the study.
The scientists also discovered that neck fleeces, or neck gaiters, often
worn by runners, were the least effective and actually allowed more
respiratory droplets to escape than not wearing a mask at all.
That’s because they were shown to break down larger droplets into
smaller particles, allowing them to slip out the sides of the covering
more easily.
“We were extremely surprised to find that the number of particles
measured with the fleece actually exceeded the number of particles
measured without wearing any mask,” Martin Fischer, one of the study’s
authors, told CNN.
“We want to emphasize that we really encourage people to wear masks, but
we want them to wear masks that actually work.”
To test the masks, the scientists made use of a black box outfitted with
a laser and a cellphone camera.
Someone wearing a face mask would speak in the direction of the laser
beam inside the box. Then the amount of respiratory droplets scattered
by the beam were recorded by the camera in the back of the box.
A computer algorithm counted the droplets seen in the video to determine
how many had leaked through.
The researchers said this was a low-cost, effective method to test which
face coverings worked and which didn’t.
“This is a very powerful visual tool to raise awareness that very simple
masks, like these homemade cotton masks, do really well to stop the
majority of these respiratory droplets,” Fischer told CNN.
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