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New U of M study looks at how COVID-19 travels indoors

The study looked at aerosol spread in an elevator, a classroom and a supermarket.

MINNEAPOLIS — Researchers at the University of Minnesota hope a new study will help businesses and schools make their indoor spaces safer.

Preliminary results have been released from the study done by the U of M's College of Science and Engineering, analyzing how the coronavirus spreads indoors. The aiborne virus transmission was modeled through aerosols, which come out of our mouths when we breathe and speak.

The study found that when an infected person breathes or speaks, the COVID-19 virus "hitches a ride" on those aerosols as they land on nearby surfaces or be inhaled by others.

The study looked at the virus spread through aerosols in an elevator, a classroom and a supermarket. They used measurements of aerosols released by eight asymptomatic COVID-19 carriers. They then compared how the virus fared with different levels of ventilation, and different spacing among occupants.

Read the full study: Risk assessment of airborne transmission of COVID-19 by asymptomatic individuals under different practical settings

Researchers found that in indoor spaces, good ventilation will filter some of the virus out of the air, but may leave more particles on surfaces. In a classroom setting simulation, only 10% of the aerosols were filtered out by ventilation when an asymptomatic teacher was talking for 50 minutes.

“Because this is very strong ventilation, we thought it would ventilate out a lot of aerosols. But, 10 percent is really a small number,” said assistant professor Suo Yang. “The ventilation forms several circulation zones called vortexes, and the aerosols keep rotating in this vortex. When they collide with the wall, they attach to the wall. But, because they are basically trapped in this vortex, and it’s very hard for them to reach the vent and actually go out.”

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The researchers were able to map the air flow and find "hot spots" where the virus aerosols congregated. With the right combination of ventilation and organization of people, they believe it could be possible to mitigate the spread and avoid these hot spots.

In a classroom setting, for instance, the virus spread more when the teacher was directly under an air vent. If classrooms were arranged and disinfected in certain ways, it could help mitigate that spread.

“In general, this is the first quantitative risk assessment of the spatial variation of risks in indoor environments,” said mechanical engineering associate professor Jiarong Hong. “You see a lot of people talking about what the risks are of staying in confined spaces, but nobody gives a quantitative number. I think the major contribution we’ve made is combining very accurate measurements and computational fluid dynamics simulation to provide a very quantitative estimate of the risks.”

Yang and Hong believe that the research will help indoor spaces like movie theaters and other places with large gatherings plan for a safer environment. They are also working with the Minnesota Orchestra to provide them with a plan to minimize the risk in Orchestra Hall.

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The state of Minnesota has set up a data portal online at mn.gov/covid19.

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