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How the Coronavirus Spreads Indoors and What Can Be Done About It

  • Researchers have pinpointed how the novel coronavirus spreads through indoor places such as schools and stores.

  • They say revamping HVAC systems can help slow the spread.

  • Less expensive solutions include opening windows and installing better air filters.

  • Experts advise people to wear facial coverings regardless of how efficient a building’s air circulation system is.

The World Health Organization has now officially recognizedTrusted Source that the novel coronavirus can be transmitted through the air via tiny aerosol particles emitted when we talk, cough, or breathe.

This proclamation has led to more questions about airborne transmission of the virus that causes COVID-19.

Chief among them is how to stop that airborne transmission, particularly indoors.

This will be an even more pressing question if state and local governments go through with plans to reopen schools this fall.

A key part of reducing that indoor spread of the virus could be air circulation. That includes using windows as well as the circulation systems already installed in buildings.

However, a new study concludes that those systems may have a limited ability to remove the virus from the air of rooms and buildings.

The study’s researchers also emphasize that how those systems are set up is a key factor.

There are some measures that experts say may help — without costing too much time or money. These include increasing the amount of fresh air indoors, upgrading filters, and properly wearing masks.

What researchers learned

In the new study, researchers measured how the virus travels through the air indoors by studying the movement of aerosols from eight people with COVID-19 who were asymptomatic — and how ventilation systems and spacing affected that flow.

The researchers found that good ventilation filtered out some of the airborne virus, but the majority of virus-carrying particles were left behind on surfaces.

In a classroom, ventilation filtered out just 10 percent of the aerosols emitted by an asymptomatic teacher talking for 50 minutes.

Part of the issue was that the ventilation formed vortexes where the aerosols were caught in a spinning cycle. This made it difficult for those aerosols to reach the vent to exit the room.

Reducing these “hot spots” where virus-carrying aerosols accumulate requires thinking about how the ventilation is set up, the researchers said.

“What we found from the classroom simulation is actually the placement of the ventilation is very important,” Jiarong Hong, PhD, MS, an associate professor of mechanical engineering at the University of Minnesota and one of the authors of the new study, told Healthline.

“The potential hot spots are where air is coming in or out,” he added.

In general, though, the more ventilation, the better.

That could be by opening windows or, Hong said, adding vents in ceiling panels.

“To reduce risk, you have to increase the ventilation sites whenever possible,” he noted.

Hong said an air filtration system would ideally be placed as close as possible to the person who is producing the most aerosols — in a classroom, typically the instructor.

If it’s possible to have additional air filtration units they could be placed in the middle of tables, he suggested.


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