Improving Ontario school ventilation: Q&A with Simcoe-based energy engineer David Elfstrom

On Wednesday, the province announced another $25 million to get thousands more free-standing HEPA filters in schools before the first day, this fall. But is that enough to ensure safe schools?

There’s inequity in terms of air quality between schools and within schools, Elfstrom says

David Elfstrom is an independent energy engineer, based in Simcoe, Ontario. (David Elfstrom/Twitter)

Ventilation has become one of the key elements in stopping the spread of COVID-19 indoors. But many school buildings in Ontario lack adequate infrastructure, beyond opening a window.

On Wednesday, the province announced $25 million to get thousands more free-standing high-efficiency particulate air (HEPA) filters in schools before the first day, this fall. The new funds bring the province's investment in school ventilation to $600 million, it said.

But is that enough to ensure safe schools?

CBC's Metro Morning host Jason D'Souza spoke with David Elfstrom, an independent energy engineer, based in Simcoe, Ont.

Here is some of that conversation.

The discussion has been edited for length and clarity.

Q: Education Minister Stephen Lecce has promised to put HEPA filters in all classrooms, school gyms and libraries that don't already have mechanical ventilation systems. Break it down for us — what is the difference between mechanical ventilation and a HEPA filter?

David Elfstrom: Mechanical ventilation is intentionally introducing fresh outdoor air into a space and then removing the stale air at the same time. About 70 per cent of schools in Ontario have a full ventilation system and the other 30 per cent have either nothing, or exhaust-only ventilation, which means there is maybe an exhaust at the front of the classroom on the opposite side of the windows that extracts air. And then fresh air comes in through cracks and through open windows. The HEPA filter is a little different. It is filtering the air of all the particles that could be floating around in the air.

Q: Do we know which one is more effective, especially when it comes to something like COVID-19?

DE: They're essentially equal in that you can combine the two to achieve a total effective ventilation rate.

Q: What do we know about the dangers, the concerns that exist with the way classrooms are set up right now with respect to COVID-19 possibly being spread in the air?

DE: The main issue is we don't really know because it hasn't been measured in many classrooms. Other jurisdictions such as New York City and especially Philadelphia have gone in and physically measured the amount of air changes per hour in each room and have closed them off if they're not acceptable or to a certain level.

Q: How do we get to that point where we can understand some of the data a little bit better given that there's just five weeks left before schools resume and this is a critical part of the conversation?

DE: There's not much time left. Bringing in portable CO2 metres can help at least get an indication of ventilation especially in these areas that are naturally ventilated. It doesn't tell you the effect of using a HEPA filter. A HEPA filter will not affect CO2 levels, it's not a gas filter, it's only for particles.

Q: Is it fair to say then that there's a significant level of unknown with respect to the ventilation question before kids head back to the classroom?

DE: Correct. I'd say there's a fair amount of inequity and some of the inequity is in terms of air quality between schools and within schools, and it's definitely helpful to have this new commitment to have at least some extra filtration in the schools that don't have any mechanical ventilation. It's put us a leader as a province in Canada, when B.C. and Alberta have nothing, so it's not a high bar to achieve.

Q: It's one thing for these kids to be back in the classroom come September but we're learning as part of the back-to-school policy that music classes will resume and that means playing a lot of wind instruments, it means high-contact indoor sports will be allowed once again. How do the actual activities impact one's experience in the classroom with respect to air quality?

DE: In general, the air quality is a bit different from what we're talking about with COVID. For COVID, we know that these types of respiratory activities, singing especially, can create lots of extra aerosols in the air that could contain the virus and it does concern me that there seems to be a good focus on filtration and ventilation but at the same time increasing the risk from some of these activities doesn't seem to make too much sense to me.

Q: For parents who are already anxious about sending their kids back into the classroom, how would you describe what your ideal scenario would look like as far as ventilation plans go within schools?

DE: The ideal would be knowing what the school has done in each classroom and if it hasn't done something that's important to know as well. For those classrooms who are receiving a HEPA filter, the noise issue is a potential concern so it does have to be sized correctly and it does have to have limits on the actually volume of these because if they're too loud people won't use them, they'll turn them down so that they can actually have an educational experience.


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