A new study explains how the coronavirus droplets released when you cough, sneeze or speak, travels around a room. Researchers from the University of Minnesota hope their work will help schools and businesses reduce the chance of COVID-19 transmission.
In the study, they created a model of how these aerosol droplets can travel in indoor spaces such rooms, elevators and supermarkets. They also compared how the coronavirus survived in different types of ventilation and with different spacing of people within a room.
“You see a lot of people talking about what the risks are of staying in confined spaces, but nobody gives a quantitative number,” said co-author Jiarong Hong, an associate professor of mechanical engineering. “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,” he said in a university news release.
The researchers found that good ventilation can filter out some of the virus, but it can remain on surfaces. They ran a simulation in which an asymptomatic teacher spoke for 50 minutes straight. They found that only 10% of aerosols were filtered out, and of the particles remained on the walls.
“Because this is very strong ventilation, we thought it would ventilate out a lot of aerosols. But 10% is really a small number,” said co-author Suo Yang, an assistant professor of mechanical engineering.
He noted that the ventilation forms vortexes – expelled aerosols rotate within those vortexes rather than exiting.
“When they collide with the wall, they attach to the wall,” Yang added. “But, because they are basically trapped in this vortex, and it’s very hard for them to reach the vent and actually go out.”
The researchers followed the airflow to find virus hot spots where the aerosols congregated in the room. They also found that the aerosols spread significantly less throughout the space when the teacher was placed directly under an air vent.
“After our work goes out, I think more people will ask for help because I think many businesses reopening will have this need — movie theaters, drama theaters, any place with large gatherings,” Yang said. “If you do a good job, if you have good ventilation at the right location, and if you scatter the seating of the audience properly, it could be much safer.”
The report was published online on July 28, and was not yet peer-reviewed.