Filenews 16 September 2021
We have now learned to live with stickers on the floor of indoor spaces, such as inside hair salons and shops, which define the distance of two meters that we must keep in order to be protected from the new coronavirus – in fact from the droplets that can be released by a virus-infected person who may be near us. But is this distance enough to avoid the aerosol, the tiny droplets in the form of sprays that can have a very high viral load and remain in the air for a long time?
SOS indoors
No, it's not enough indoors, researchers from the Pennsylvania State University School of Architecture (Penn State) respond, with their publication in the journal "Sustainable Cities and Society" (the results are available online before they are published in the printed version of the journal in the October issue).
"We explored the aerogenic transport of particles that carried the virus and were released by infected people inside buildings," explained Zen Pei, first author of the study and a PhD student in Architectural Engineering at Penn State. "We investigated the effect of building ventilation and social distancing as control strategies for exposure to airborne viruses indoors."
Three factors under the microscope
The researchers looked at three factors: the amount of air and the rate at which it is renewed within a space, the different ventilation strategies of the space, as well as the way of aerosol release when one exhales and when someone speaks. They specifically focused on aerosols of the human respiratory system with a size of one to 10 micrometres (particles of such magnitude can carry SARS-CoV-2).
Journey in record time of one minute
"According to our results, particles that carry the virus and are released by an infected person when they speak and do not wear a mask can quickly travel – in fact within a minute – to the breathing zone of another person, even if these two individuals keep a distance of two meters," Dr Rim noted, lead author of the study, associate professor of Architectural Engineering at Penn State. "This is more pronounced in places where there is not enough ventilation. The results testify that social distancing alone is not enough to prevent exposure to the aerosol and should be enforced in conjunction with other control strategies such as the use of masks and adequate ventilation indoors."
Seven times higher concentrations in dwellings
Scientists have discovered that the aerosol travels farther and faster in rooms where there is displacement ventilation, where fresh air constantly flows from the floor and pushes the "old" air into a ventilation shaft near the ceiling. This type of ventilation system has many dwellings where, as it turned out, each person can be exposed to seven times higher aerosol concentrations with the virus compared to buildings where there is a mixed ventilation system. Many commercial properties have a mixed system, which incorporates the outside air into the air of the interior, thus diluting it and eventually leading to lower aerosol concentrations, according to the researchers.
Greater risk in homes than offices
"This is one of the unexpected results. The likelihood of aerogenous infection can be much greater inside homes than inside offices," noted Dr. Rim. "But in homes, the use of fans and air purifiers can help reduce the chances of infection." According to the professor, other measures – such as the use of masks – must be observed indoors in order to reduce the risk of airborne transmission.
Analysis in classrooms and public transport
The research team is now applying this analysis technique to different indoor spaces, such as classrooms and public transport in order to calculate how much the risk of airborne transmission of the virus in these environments may increase.
