Widespread use of better face masks and good ventilation can help mitigate the spread of Covid-19 indoors, a study has shown.
The findings, published in the journal Physics of Fluids, showed a significant buildup over time of aerosol droplets -- exhaled droplets so tiny they remain suspended and travel through the air -- despite the use of common cloth and blue surgical masks.
"There is no question it is beneficial to wear any face covering, both for protection in close proximity and at a distance in a room," said Serhiy Yarusevych, Professor of mechanical and mechatronics engineering.
"However, there is a very serious difference in the effectiveness of different masks when it comes to controlling aerosols," he added.
Previous research has found 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-metre social distancing zone widely recommended by public health officials.
The study showed that most common masks, primarily due to problems with fit, filter about 10 per cent of exhaled aerosol droplets. The remaining aerosols are redirected, mostly out the top of the mask where it fits over the nose, and escape into the ambient air unfiltered.
By contrast, higher-quality, more expensive N95 and KN95 masks filtered more than 50 per cent of the exhaled aerosols that can accumulate indoors and spread the Covid-19 virus when inhaled by other people.
Yarusevych noted that the much greater effectiveness of N95 and KN95 masks versus cloth and surgical masks makes a compelling case that they should be worn in indoor settings, such as schools and workplaces, as much as possible.
Experiments also quantified the impact of ventilation systems, which circulate and replace air in rooms, on the accumulation of aerosols.
Even modest ventilation rates were found to be as effective as the best masks in reducing the risk of transmission.
Ideally, 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, Yarusevych said.