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Face masks reduce the risk of spreading large droplets linked to Covid when talking or coughing by up to 99.9%, according to a lab experiment with mechanical mannequins and human subjects, researchers said Wednesday.
A woman standing two meters from a coughing man without a mask will be exposed to 10,000 times more such droplets than if he were wearing one, even if he was only 50 centimeters away, they reported in the journal Royal Society Open Science.
“There is no doubt that face masks can dramatically reduce the dispersion of potentially virus-laden droplets,” lead author Ignazio Maria Viola, an expert in applied fluid dynamics at the School of Engineering, told AFP. ‘University of Edinburgh.
Large respiratory droplets – which act like projectiles before being fired towards the ground by gravity – are believed to be the main driver of the transmission of SARS-CoV-2, he noted.
The smaller ones, sometimes called aerosol droplets, can stay airborne for longer periods of time.
“We are continually exhaling a whole range of droplets, from micro-scale to millimeter scale,” Maria Viola said over the phone.
“Some droplets will fall faster than others” depending on temperature, humidity and especially air speed, he said.
The study focused on particles larger than 170 microns in diameter – about two to four times the width of a human hair.
Aerosol particles, which tend to follow currents in air, are generally described as smaller than 20 or 30 microns.
Intermediate-sized droplets can behave in both directions, according to the study.
– Wearing the universal mask –
“If you wear a mask, you reduce the transmission of the virus by an order of magnitude – 10 times less,” said Maria Viola.
“In our study, for the larger droplets that we measure, we are talking about 99.9% less.”
According to the Institute for Health Metrics and Evaluation (IHME) in Seattle, Washington, 55,000 lives could be saved in the United States over the next four months if a universal mask use policy is adopted.
Institute modellers – who accurately predicted in mid-July that Covid-19 deaths in the United States would exceed 224,000 as of November 1 – predict 561,000 deaths on current trends by April 1, 2021.
Wearing a universal mask would reduce the number of deaths worldwide by 400,000 over the same period, from 2.9 million to 2.5 million, they calculate. To date, the virus has claimed an estimated 1.7 million lives.
Earlier this month, the World Health Organization (WHO) updated its Covid-19 guidelines on masks to recommend that they be worn indoors in the presence of other people if ventilation is insufficient.
The guidelines apply particularly in areas of known or suspected community transmission.
Masks are primarily used to reduce the emission of virus-laden droplets from people who cough, sneeze, sing, speak, or simply breathe, but they can also help prevent droplet inhalation by the wearer.
“Sheet masks not only effectively block most large droplets – 20-30 microns and larger – but they can also block the exhalation of fine droplets and particles, also often called aerosols,” according to the CDC.
mh / gd
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