Masks block 99.9% of large COVID-related drops: study

Large respiratory droplets are considered to be the main driver of SARS-CoV-2 transmission.  Illustration by Banksy

Large respiratory droplets are considered to be the main driver of SARS-CoV-2 transmission. Illustration by Banksy

Facial masks reduce the risk of spreading large COVID-related drops when they speak or cough by up to 99.9%, according to a laboratory experiment with mechanical mannequins and human subjects, the researchers said on Wednesday.

A woman who stands two meters away from a man who coughs without a mask will be exposed to 10,000 times more such drops than if she were wearing one, even if it is only 50 centimeters away, they reported in the diary Royal Society Open Science.

“There is no doubt that face masks can dramatically reduce the dispersion of potentially virus-laden drops,” lead author Ignazio Maria Viola, an expert in fluid dynamics applied at the University of Edinburgh School of Engineering, told AFP.

Large respiratory droplets – which act as projectiles before being pulled to the ground by gravity – are considered to be the main engine of the SARS-CoV-2 transmission, he noted.

The smallest, sometimes called aerosol droplets, can remain suspended in the air for longer periods.

“We continuously exhale a whole range of drops, from micro-scale to millimeter scale,” Maria Viola said by phone.

“Some drops 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 air currents, are generally described as being smaller than 20 or 30 microns.

Studies have found that drops of intermediate size can behave in both directions.

Worn universal mask

“If you wear a mask, attenuate the transmission of the virus by an order of magnitude – 10 times less,” said Maria Viola.

“In our study, for the larger droplets we measure, we speak 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 were adopted.

The Institute’s modelers – who predicted exactly in mid-July that COVID-19 deaths in the US will exceed 224,000 by November 1 – project 561,000 deaths on current trends by April 1, 2021.

The universal wearing of the mask would reduce the total number of deaths by 400,000 in the same period, from 2.9 million to 2.5 million, they calculate. To date, the virus has claimed about 1.7 million lives.

Earlier this month, the World Health Organization (WHO) updated its COVID-19 guide on masks to recommend wearing indoors in the presence of others, if ventilation is inadequate.

The guidelines apply in particular to known or suspected areas of Community transmission.

Masks are primarily used to reduce emissions of virus-laden drops when people cough, sneeze, sing, talk or simply breathe, but they can also help prevent the wearer from inhaling the drops.

“Cloth masks not only effectively block most large droplets – 20-30 microns and larger – but can also block the expiration of fine droplets and particles, often called aerosols,” according to the CDC.

Masks are not enough to stop the spread of COVID-19 without distancing: study

More information:
Lucia Bandiera et al. Covering the face and dispersing the airway droplets, Royal Society Open Science (2020). DOI: 10.1098 / rsos.201663

© 2020 AFP

Citation: Masks block 99.9% of large drops related to COVID: study (2020, December 23) taken on December 23, 2020 from linked-droplets. html

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