U of M study details how coronavirus spreads in classrooms

Without standing directly under a vent, 90% of aerosols from a teacher remain in the classroom, the study found.
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On Tuesday, just two days before Gov. Tim Walz and the Department of Education were set to announce back-to-school plans in Minnesota, the University of Minnesota College of Science and Engineering released findings from a research project that analyzed how the coronavirus spreads in classrooms. 

Researchers modeled airborne virus transmission through aerosols that are ejected from the mouth as people breathe and speak. The virus can spread as it "hitches a ride on those aerosols as they land on nearby surfaces or are inhaled by another person," a release from the U of M said. 

The study involved eight asymptomatic patients with confirmed COVID-19 infection.

The classroom study featured an infected patient playing the role of a teacher who consistently spoke for 50 minutes. That simulation resulted in just 10% of the aerosols released from the subject's mouth being filtered out of the room, with the "majority of particles" being "deposited on the walls." 

“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 Sue Yang, assistant professor of mechanical engineering. 

“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.”

While 90% of the virus particles were left in the classroom, the U of M noted that aerosols are likely to spread significantly less around the room when the teacher does the majority of their talking when standing or sitting directly under an air vent. 

The study found that it may be possible to avoid "hot zones" where the virus congregates through "the right combination of ventilation and interior organization." 

“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," said Yang. 

Walz and the Department of Education are considering three back-to-school scenarios: 

  1. Distance learning
  2. In-person instruction
  3. Hybrid model involving distance learning and in-person instruction

Minneapolis Public Schools, on Tuesday, revealed that it will bring students into the 2020-21 school year through distance learning, though students will have options for tutoring and other forms of more direct communication and instruction. 

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