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HEALTH – Wearing a mask is fine, but wearing a valve mask is less so. Experts have repeatedly pointed this out since the outbreak began, but a recent study appeared on November 11 in the journal Fluid physics just confirm it.
Matthew Staymates, fluid mechanics and dynamics engineer, author of this study, analyzed different types of masks to determine which are the most effective in reducing coronavirus transmission. And it turned out that the valve of the studied N95 masks (designed specifically for healthcare professionals) was problematic.
Used to improve the comfort of the user (who thanks to it feels less resistance during exhalation), this valve is “essentially a small flap that opens during exhalation, and leaves the air ‘s. escape without being filtered through the mask material, “says Matthew Staymates.
To reach this conclusion, the researcher designed a manikin by programming it to breathe like a human, and observed the exhaled particles with an N95 valve, then with a valveless mask. The difference between the two is obvious, as can be seen in the video below, made using a stream visualization method.
Filtration of droplets rejected during exhalation is therefore much less important with a mask with a valve than with a mask that does not have one.
Exposing others to the virus
To make the “cloud” of droplets visible, the researchers used a computer algorithm to measure its density in pixels. Beware though, the size of the expired droplet cloud says nothing about its viral load, it simply shows its density (higher with a valve).
“According to what we know today, Covid-19 is transmitted in part by respiratory droplets, so the N95 valves are not made to control the pandemic at its source,” the researcher emphasizes.
Requested by the site Popular scienceMartin Fischer, professor of chemistry at Duke University (North Carolina, USA), says it is a “very accurate visualization tool”. He also explains that some valve masks have filters and are more effective than others, but that “you can’t really tell by buying them fast.” It is therefore better to skip the turn anyway.
As the site points out Forbes, these valve masks were originally designed to protect the wearer from inhalation. Dust on a construction site, or germs and viruses in the hospital, in particular. But they were less designed to protect others.
In September, another study, published in the same journal, came to the same conclusion for valve masks, but also for visors.
In a document that answers all questions about protective masks, the National Research and Safety Institute (INRS) indicates that the valve is indeed “liable to contaminate the external environment”. With a valve mask, you are therefore protected from the coronavirus. But you can unmask the people you meet.
See also on The HuffPost: These teachers tell the story of teaching with a mask
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