Masks, air purifiers could slash odds of coronavirus spread in classrooms: SU report

covid testing at ESM high school

Teachers in the East Syracuse Minoa school district were tested for coronavirus at the high school gymnasium Aug 31, 2020. A nasal and saliva test were given by nurses from Nascentia. Dennis Nett | dnett@syracuse.com

Syracuse, N.Y. – A new paper by a Syracuse University professor has some good news and some bad news for parents and school districts as the academic year approaches.

The good news: Districts can slash the odds of students infecting each other with the novel coronavirus if classrooms have good air flow and kids wear masks.

The bad news: Buildings have to be very well-ventilated (not an easy task) and kids have to wear their masks properly (show us a kid who can do this for a full school day).

“Good masking and good ventilation together are very good,” said Eric Schiff, a physics professor who wrote the paper. “But some classrooms are not going to achieve that level (of ventilation), and I don’t know how successful teachers are going to be in getting students to cooperate.”

The report comes as school districts in Central New York are struggling with how to reopen after the coronavirus pandemic forced their abrupt closure in March. Some districts plan a hybrid of online and in-school learning, and many have pushed back when they’ll bring students into buildings. The Syracuse city district, the region’s largest, will offer online learning only until at least Oct. 5.

School reopening plans emphasize social distancing, mask-wearing and hand-washing. The state education department “strongly recommended” students wear masks in class, but they are only required when students can’t maintain appropriate social distancing. About 70 percent of districts have opted to require masks in class, according to the state’s largest teachers’ union. Several districts in Central New York have said they won’t force students to wear masks while receiving instruction.

Experts in how the virus moves through the air are urging schools to pay close attention to ventilation, too.

Schiff’s paper looked at a hypothetical 20-person, 600-square-foot classroom where one student carrying the virus is highly infectious, or a “super spreader.” With poor ventilation and no masks, 80% of students would contract the virus if they were all in the same room for four hours, the report says.

With very good ventilation and everybody wearing surgical masks the entire time, Schiff estimated, just 2% of the class was likely to be infected. With cloth masks, it’s about 5%.

Schiff concedes he makes some “bold assumptions” in the paper, which is based in part on a study of a poorly ventilated restaurant in China where one person spread the virus to diners at other tables. Schiff’s paper notes that “super spreaders” – people who can be 100 times as infectious as the typical Covid-19 patient – are rare. His report is also limited to classrooms, where students would spend most of their day, and so doesn’t consider transmission risks of other areas of the school, such as gymnasiums, music rooms or cafeterias.

Ventilation is measured by air exchanges, described as the number of times that air is pulled from the room and replaced with fresh air. A good air flow would be three exchanges per hour; excellent would be five or six per hour. The more air that flows through a room, the quicker it will push any virus out and reduce how much of the virus people are inhaling.

Classrooms will vary widely in air exchanges per hour. Some might be as low as one air exchange per hour, which would allow the virus to accumulate and be inhaled by others in the room.

“Schools have been designed to a standard that’s set for energy efficiency, not infectious disease control,” said Joseph Allen, a professor of exposure assessment science at Harvard University’s T.H. Chan School of Public Health.

It’s difficult to retrofit old buildings with a system that can increase air flow by five or six times, said Cliff Davidson, an SU engineering professor who works with ventilation systems. Another solution is for a school district to install high-efficiency filters in the air-handling system that would trap the virus so it doesn’t get recirculated.

The downside to those filters is because the holes are so tiny, it’s harder to push air through them. That means bigger, stronger fans have to be installed, too.

“Pressure drops when air goes through those filters, and it takes a lot of energy to push the air through the fibers,” Davidson said. “We need to have ventilation fans that are strong enough to push the air through the filters, and we need enough of that filtered air to go into a classroom.”

Retrofitting an entire school’s air system with new filters and stronger fans would be time-consuming and expensive. Experts say schools can use short-term, cheaper alternatives that will help clean classroom air.

“Start opening up windows,” Allen said in a conference call with reporters. “We’ve measured this, and sometimes you can get five, six, seven even 10 air changes per hour by opening windows.”

Windows only need to open 6 inches to make a substantial difference, Allen said.

Adding fans in windows to blow air outside also helps clear the virus, Davidson said.

“You can put fans in windows and have very high exchange rate,” he said. “But as the weather gets colder, that’s not going to be feasible at some point.”

That’s where air purifiers come in, experts agree. The right units, which cost about $500 each, can substantially reduce the amount of virus circulating in the air, Schiff said.

“You can easily get up to three air exchanges with air purifiers without breaking the bank,” he said. “Several small air purifiers running in a classroom might be enough to tip the scales.”

Good luck finding those now, Schiff said. HealthWay Family of Brands, an Oswego County company, just will supply 10,000 portable air purifiers to the New York City school system, the nation’s largest. Company president Vinny Lobdell Jr. said the company is running shifts 24 hours a day and still has stock.

Something is better than nothing, Schiff said, even if it’s small air purifiers and a single open window. He said his paper offers two pieces of advice for school officials.

“Put air purifiers in rooms where you can’t get six air exchanges an hour and develop the necessary rapport with your students to get them to cooperate on masking,” he said. “If they’re put together, schools will not be a significant vector in spreading the virus.”

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