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Winter is coming and COVID is here: Why ventilation in schools matters

Last updated: 10-12-2020

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Winter is coming and COVID is here: Why ventilation in schools matters

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Winter is coming and COVID is here: Why ventilation in schools matters
"We have systemically neglected our HVAC systems, especially in schools," says Jeffrey Siegel, a University of Toronto engineering professor.
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Oct 10, 2020  •   •  6 minute read
Professor Jeffrey Siegel, a professor in the Department of Civil & Mineral Engineering at the University of Toronto's Faculty of Applied Science & Engineering. Photo by Tyler Irving /University of Toronto Engineering
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The Ontario government announced that it was giving school boards $50 million for ventilation upgrades in schools in August.
Days later, the province urged school to spend the money by Thanksgiving. But, with about 5,000 schools in the province, that means that on average there will only be about $10,000 a school to improve ventilation and help prevent the transmission of COVID-19.
The Ottawa-Carleton District School Board has received almost $1.7 million in supplemental provincial funding.
The money will be spent on more frequent air filter changes, air purifiers for spaces with limited fresh air intake and additional monitoring and calibration of HVAC systems, spokesman Darcy Knoll said.
Staff have been inspecting schools and systems over the past several months to ensure they’re functioning as designed.
Repairs are being completed and the board has reviewed proposed strategies with Ottawa Public Health for commentary based on observations of the behaviour of the virus over the past several months, Knoll said.
“That ongoing dialogue continues to be very useful in informing our work.”
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The Ottawa Catholic School Board is receiving $958,500 for ventilation.
“We have completed our preventative maintenance work over the summer and are currently working with commissioning consultants to check, test and optimize the operations of our mechanical ventilation systems,” spokeswoman Sharlene Hunter said.
Among other projects, the money is being spent on HVAC equipment inspections and recommissioning and increasing the frequency of filter change. The board is in the process of purchasing stand-alone HEPA filters for higher-risk areas, such as isolation rooms, and hopes to have them in the coming weeks.
“Although ventilation is an important component of indoor air quality and mitigation measures to reduce the spread of COVID-19, our best and most effective effort is in the ongoing cleaning and disinfection of our schools,” Hunter said.
“We have systemically neglected our HVAC systems, especially in schools,” said Jeffrey Siegel, a professor of civil engineering at the University of Toronto, who also holds an appointment at the Dalla Lana School of Public Health.
“If there is any silver lining to COVID-19, it’s that people are thinking about indoor air,” he said.
Siegel researches the control of particles indoors and the indoor microbiome. This newspaper asked him about schools, ventilation and why the coming of winter had him concerned.
Q: There are a lot of building standards around indoor air quality. Do any specifically address preventing the spread of infectious diseases?
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A: Not really. There’s a standard for health-care settings. There’s a ton of evidence from the Centers for Disease Control and the World Health Organization that are interpreted as standards. The problem with a standard that directly addresses infectious diseases is that it would have to be very disease-specific. Ventilation has the benefit of reducing infectious diseases, but right now we can’t say, “Double the ventilation will reduce the transmission of disease X by Y amount.”
Q: What are the indoor risk factors for COVID-19 airborne transmission?
A: There are three factors: crowded spaces, poorly ventilated spaces and more time spent in that environment. When all three factors are present, the risk is very high. It diminishes as we address these factors.
Q: Would reducing class sizes help?
A: Absolutely. There are two effects when you have smaller class sizes. Students are farther apart and there are fewer infections coming into the cohort. If there is transmission, the cohort is smaller, so fewer people will be potentially infected.
Q: What’s the difference between droplets and aerosols?
A: Droplets are bigger then five microns and aerosols are smaller than that. Droplets are assumed to settle rapidly within two metres. But this is a poor assumption in indoor environments. Droplets shrink to smaller sizes as water evaporates from the droplet. Air is never still in a building. Indoor air currents can carry droplets outside the two-metre range. Physical distancing is good. The farther away you are from someone else, the better, but it’s not perfect protection. There was a very good paper recently on influenza that looked at respiratory droplets that fell on the floor. They can be “resuspended” — essentially kicked into the air. When you think about walking across a floor, you kick up a little cloud of particles.
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Q: What’s your concern as we head into winter?
A:  When the heat goes on and the air is dry, water from droplets evaporates. It happens very fast. You have a particle droplet that starts out large. All of a sudden, it shrinks and it travels much farther.
Q: Is opening windows a good way to help reduce the risk of transmission?
A: It helps. But I can’t tell you it’s always protective. Open windows cause other problems. Some schools are located in places where ambient air quality is poor near pollution sources such as major roadways, industrial areas, construction activity and some types of agricultural activities. Not all Ontario schools have windows that open. I want it to be on the list of strategies, but I don’t want it to be the magic solution.
Q: Do new schools have better ventilation than old schools?
A: You can have two schools in Ottawa built at the same time and operated by the same facilities staff that have different risks for transmission. Quality and age are not as closely related as you might think. There are buildings constructed in all time periods of high quality and buildings constructed in all time periods of low quality.
Q: Is recirculated air necessarily bad?
A: About 15 to 20 per cent of the air in a typical building comes from the outside. The rest is recirculated. Recirculated air doesn’t have to be bad if it’s filtered well. There are some very good filters and they’re not that expensive, but they have to be installed properly. In a lot of buildings, there are spaces in the rack and the air just moves through those spaces rather than through the filter. But, even if there is a good filter, some classrooms might not get that good filtered air. Maybe some of the ducts weren’t laid out properly. Filtration can make a big difference, but it has to be done well.
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