Study supports widespread use of better masks to curb COVID-19 indoors – ScienceDaily

Engineering researchers at the University of Waterloo performed experiments using a mannequin to simulate a person sitting breathing in a large room. Studies have shown a significant build-up over time of aerosol droplets – exhaled droplets so tiny that they stay suspended and travel through the air – despite the use of common tissues and blue surgical masks.

“There is no doubt that it is beneficial to wear a face covering, both to protect yourself near and from a distance in a room,” said Serhiy Yarusevych, professor of mechanical and mechatronic engineering and head of the ‘study. “However, there is a very serious difference in the effectiveness of different masks when it comes to controlling aerosols.”

Previous research has shown that aerosols dispersed by infected people are a source of transmission of the SARS-CoV-2 virus that causes COVID-19, even outside the two-meter social distancing zone widely recommended by officials of public health.

The study showed that the most common masks, mainly due to fit issues, filter about 10% of exhaled aerosol droplets. The remaining aerosols are redirected, mainly to the top of the mask where it fits on the nose, and escape into the ambient air without a filter.

In contrast, the better and more expensive N95 and KN95 masks filtered over 50% of exhaled aerosols that can build up inside and spread the COVID-19 virus when inhaled by other people.

Yarusevych, principal investigator of the Fluid Mechanics Research Lab, said that the much greater effectiveness of N95 and KN95 masks compared to fabric and surgical masks argues for their wearing as much as possible in indoor environments, such as schools. and workplaces.

“Much of this may sound like common sense,” he said. “There is a reason, for example, why doctors wear N95 masks – they work much better. The novelty here is that we have provided solid numbers and rigorous analysis to support this hypothesis.”

Experiments have also quantified the impact of ventilation systems, which circulate and replace air in rooms, on the accumulation of aerosols. Even modest ventilation rates have been shown to be as effective as the best masks in reducing the risk of transmission.

Ideally, Yarusevych said, the evidence shows that high-quality masks and proper ventilation should be used in combination to mitigate the threat posed by aerosol buildup inside as much as possible.

The study, Experimental Investigation of Indoor Aerosol Dispersion and Accumulation in the Context of COVID-19: Effects of Masks and Ventilation, appears in the journal Fluid physics.

Yarusevych collaborated with Sean Peterson, also professor of mechanical and mechatronic engineering at Waterloo, and doctoral engineering students Yash Shah and John Kurelek.

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