Design Engineering

U of Waterloo study supports widespread use of high quality masks to stem COVID

By DE staff   

General Medical

Due to poor fit, common masks filter only 10 per cent of exhaled aerosol droplets, study finds.

This image from a video made by Waterloo Engineering researchers shows how much aerosol-laden exhalation flow escapes unfiltered when wearing (left to right) no mask, a KN95 mask and a surgical mask. (Photo credit: University of Waterloo)

A study by engineering researchers at the University of Waterloo found that common, poorly fitting face masks may do little to curb the spread of COVID-19 indoors. However, wide-spread use of higher quality N95 and KN95 masks, plus good ventilation, could significantly reduce the spread of COVID-19 indoors.

To test mask efficacy, the U of Waterloo researchers used a mannequin to simulate a seated person breathing in a large room. Testing with common cloth and blue surgical masks, the study discovered significant buildup of aerosol droplets over time. Those masks filtered approximately 10 per cent of exhaled aerosol droplets; the bulk of droplets are redirected out of the top of the mask due to poor fit. By contrast, N95 and KN95 masks filtered more than 50 per cent of the exhaled aerosols.

Serhiy Yarusevych, a professor of mechanical and mechatronics engineering and the leader of the study, said the much greater effectiveness of N95 and KN95 masks versus cloth and surgical masks makes a compelling case they should be worn in indoor settings, such as schools and workplaces, as much as possible.

In addition, the study found that even modest ventilation rates were found 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 indoor aerosol accumulation 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 Physics of Fluids.

Yarusevych collaborated with Sean Peterson, also a Waterloo professor of mechanical and mechatronics engineering, and engineering PhD students Yash Shah and John Kurelek.


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