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As the weather turns colder and people move indoors, the University of Toronto’s Colin Furness is emphasizing the importance of proper ventilation to combat the spread of the virus that causes COVID-19.

The expert in infection control epidemiology and COVID-19 pandemic management says it’s well-established in the medical community that airborne transmission is major contributor to the spread SARS‑CoV‑2. But he notes that public health regulations have often been slow to catch up, leaving many businesses and other organizations with less-than-optimal safeguards.

There is, however, a notable exception: post-secondary institutions.

Furness  University Affairs about how some universities – including U of T – are at the forefront of addressing ventilation by retrofitting HVAC systems.

At U of T for example, HVAC experts . Centralized HVAC system filters that service all parts of buildings including offices, meeting rooms and hallways, were replaced with enhanced MERV 13 filters (or the highest compatible with the existing HVAC infrastructure). Demand-control ventilation measures (typically in place to support energy conservation efforts) were disabled to maintain consistent in-air flow. Ventilation systems are turned on two hours before occupancy every morning to replace the air in entire buildings, a process known as flushing.

“Universities have expertise. They've got respect for expertise. And they have decision-making that actually incorporates that expertise,” says Furness, an assistant professor, teaching stream, in the Faculty of Information with a cross-appointment to the Institute of Health Policy, Management and Evaluation at the Dalla Lana School of Public Health.

He adds that such qualities make universities “incredibly resilient.”

Furness has even gone so far as to test the air quality in his own classroom.

To learn more about why HVAC systems matter, U of T News spoke with Furness about airborne transmission of SARS‑CoV‑2and how to guard against it.

Why is having proper ventilation so important in combatting COVID-19?

In the earliest days of the pandemic, we relied on our existing knowledge around transmission. It was a model that said large droplets are it and therefore we don't need to worry about air – but that view was flawed. It allowed us to explain a communicable respiratory disease, even though it wasn't quite correct.

We now know that not only does COVID-19 move through the air, but that air seems to be the dominant mode of transmission. That's a very new way of thinking. It means we have to unlearn a lot about what we thought we knew about respiratory disease. We've learned more about respiratory disease transmission in the last year and a half than I think we ever have. It's a really big deal.

It seems like universities adapted fairly quickly, compared to other organizations. Why do you think that is?

Universities have expertise. They've got respect for expertise. And they have decision-making that actually incorporates that expertise. Those are three things that make universities incredibly resilient.

We didn’t wait for others to say air matters. The leading voices in Canada are here at the U of T with respect to infectious disease and epidemiology. We consulted our own internal expertise.

U of T jumped in from the beginning and started prioritizing air and ventilation, which is really smart.

Can you explain why proper HVAC systems are effective in combating the virus?

What we understand with airborne transmission is that, if you’re infected and you exhale, the virions of the virus – viral particles – are going to stay in the air for a long time and they’re going to accumulate in the air. In other words, an infected person sitting in a room is going to continue to add to the concentration of dangerous virions in the room.

What ventilation does is it take those virions and flush them out of the room by changing the air.

You can have two people in a very well-ventilated room – one sick, one not, and the person who’s not sick is perhaps not going to get sick because they're not breathing in the unadulterated exhalations of the other person. They’re also breathing in fresh air.

Can you talk about what you’ve found testing the air quality in your classroom?

I work in a building that has forced air circulation. It has mechanical systems that can be adjusted to do what they do best. They not only circulate air, but they also exchange air from the inside the room with the air from outside the building. 

In my classroom, I’ve measured the CO2 levels. The more carbon dioxide there is in the room, the more exhalations you have as opposed to fresh air. Outdoor air is about 400 parts per million in carbon dioxide. That’s the gold standard. If you’ve got air that is higher than 1,500 parts per million, you’ve got stale air.

With COVID-19, the best practice says you should try and stay under 800 parts per million, which is very aggressive. I found my classroom is usually around 460 to 520 – so very, very close to outdoor air. I’ve got 25 students in this class and the room is big and the other thing is, at the moment, the building is sparsely populated. So, as more people start to spend more time there, we might expect those numbers to creep up a little bit. But I was flabbergasted. I bought a second unit because I didn’t think the air could be that good.

I want to point out that I’m lucky. There are many buildings that don't have forced air where managing air quality is going to be a lot harder. And you've got other kinds of challenging places like university residences and labs that have people working in close proximity and pretty complicated infrastructure. I mean, a university is a city within a city. So, I do want to acknowledge it's not always easy.

I’m going to run through three scenarios that people might find themselves in this winter. Can you weigh in on what can be done to improve air flow?

a.     On public transit or in a taxi

If you’re on a bus, streetcar or taxi, open a window. There was  around where’s the best place to sit in a taxi – in the backseat, kitty-corner to the driver.

They came to that conclusion not by measuring distance, but by modelling airflow when you have the windows open. But regardless of where you're sitting, open the windows and let the air move through. And wear an N95 mask. That’s what people should be doing to stay maximally safe.

b.    In your own home

Part of it will depend on who else is in your home. Do you share air with other dwellings? Condos and apartment buildings might have a higher risk profile depending on how air moves. But even if you’re in a single-family house and you have control of your own air, then you still want to ask: What are the risks in my house?

In my case, we’ve got two kids. One of them is under 12 and they’re both in school. They’re getting exposed to a lot of other kids and the younger one is not vaccinated. What we did at my home last fall was buy portable HEPA filters – about eight of them. I thought: If someone comes home with COVID-19, we may see transmission before we know it’s a problem. We’re not going to wear masks at home, so I thought we should be scrubbing the air as much as possible.

Opening your door or window for 10 minutes can be transformational. If you want to measure carbon dioxide in your house, you can buy a detector – which I recommend – and you can really start to get a sense of what it takes, in terms of human activity in one room, for carbon dioxide to go way up, and what it takes in terms of opening a window or a door for 10 minutes for carbon dioxide levels to go back down.

So, it’s opening windows, periodically measuring carbon dioxide and deploying HEPA filters.

c.     In a bar or restaurant

Unfortunately, my advice is not to go. At this point in the pandemic, sharing air with people who you don’t know and not wearing a mask while you’re indoors is not something I would do. I'll re-evaluate that position when I see HEPA filters in restaurants, in gyms or in public places where people are together and not wearing masks. This, to me, is extremely high risk.

We should be putting up HEPA filters in restaurants, gyms, movie theatres and other kinds of places where people are going to be gathered together and not wearing masks.

My family loves to support our local businesses by getting takeout and that’s what we’ll keep doing until COVID-19 is subdued or we know that we’re getting clean, scrubbed air in a restaurant.

Is an air purifier a useful investment for a household?

I’m a big fan of portable HEPA filters. You do need to change the filters periodically. But the filters can be vacuumed and their life can be extended. It doesn’t need to be extremely expensive. They help with a lot – with allergies, mould, and all kinds of bacterial spores in the air.

I have just purchased a HEPA unit for my furnace as well. It’s a long-term investment in air quality – above and beyond COVID-19.