Letting it all air out: Deflating the idea ventilation can easily make schools safer

Two weeks from today, Manitoba students are supposed to be back in school. To mitigate the potential for classes becoming a new vector for coronavirus transmission, the province has attempted to heed most of Ottawa's public health advice about sending kids back to school.

Mask-wearing will be mandatory, as recommended by chief federal public health officer Dr. Theresa Tam earlier in August.

Manitoba students also won't be allowed to share supplies, will be directed to remain a metre or two apart when possible and will be grouped in cohorts to make contact tracing easier, again as Tam recommended.

On the other hand, most Manitoba school divisions are not trying to reduce their average class sizes — a move that would make two-metre physical distancing far more realistic — mainly because of the required logistics and cost.

Tam also recommended something that may not be possible in Manitoba, at least not in the short term, and certainly not to the extent most parents, teachers and students would prefer: Improve ventilation to the point where increased airflow would significantly reduce the potential for catching COVID-19.

Medical experts say increasing airflow will do little to stop the main way COVID-19 jumps from person to person indoors: Through exposure to droplets exhaled by an infected person sitting or standing less than two metres away for an extended length of time.

"Unless you are sitting under a fan that's blowing right on you," said Andrew Halayko, a respiratory illness expert at the University of Manitoba, "I don't think it will have a significant effect, because you're talking about air turbulence and movement in that six-foot zone."

In other words, most ventilation systems don't move air with sufficient force to significantly diminish the risk of droplet transmission, which occurs when people either ingest droplets or touch them with their hands and bring them into their eyes, noses or mouths.

What ventilation can do, in theory

What ventilation can do, at least in theory, is reduce the potential for the transmission of much smaller aerosolized particles, Halayko said.

"Droplets become aerosols, right? So where the ventilation kicks in or will have an impact is [when] we've got kids and teachers in a room all day and droplets are drying up and becoming aerosol particles. Then they can be cleared more effectively," he said.

The problem is, epidemiologists and medical doctors are not sure how much of a threat is actually posed by aerosolized particles in a classroom or office setting, at least compared to the well-documented threat posed by exhaled droplets.

"From a respiratory perspective, I think the chance of getting infection from the droplet is much higher than the aerosol, simply on the basis that they're much more likely to be on your hands and getting [into] your eyes," Halayko said.

Dr. Jason Kindrachuk, the Canada Research Chair in emerging viruses at the University of Manitoba, said it remains unclear how much of a threat is posed by aerosolized COVID-19 particles in places outside of operating rooms and dentist's offices, where machines turn saliva into aerosols.

"Aerosol transmission probably does occur in very specific situations. We know that in health-care settings, there is a higher likelihood and there probably are some events where this occurs," Kindrachuk said in an interview from Saskatoon.

"But we do not think, or it does not seem at least from the data, that that is the primary mechanism."

Allowing more air in isn't easy

But even if only a minority of indoor COVID-19 infections result from aerosolized particles, it stands to reason anyone in a position to be exposed to those particles would prefer they get filtered out of the air.

But this is easier said than done, especially in buildings like schools.

In Manitoba, some schools have modern ventilation systems, where air is forced through ducts. Others merely allow air to rise to the ceiling. A minority can't even open their windows.

Nonetheless, Manitoba's back-to-class framework calls for schools to hold classes outdoors when possible, open windows when possible and to allow as much outside air into the building in order to dilute the exhaled droplets inside classrooms.

But even that latter step — which sounds simple — is beyond the capacity of many schools.

"You can't just go bring in 100 per cent fresh air without relieving what you brought in, out," said Mile Rendulic, director of buildings for the Winnipeg School Division, one of the few divisions in Manitoba with a plan to address the province's ventilation recommendation.

The Winnipeg School Division plans to open windows in schools where windows do open and bring as much outside air into ventilation systems as possible. 

This may not accomplish much, as Winnipeg's highly variable climate means there may be days when it's too hot, too cold, too humid or even too allergenic to open windows or suck more outside air through intake pipes, according to the WSD pandemic plan.

Schools with heating and air-conditioning systems also may not be able to handle the added load, as sucking in outside air on a consistent basis presents a dizzying array of technical challenges, Rendulic said.

In the winter in particular, cold air would have to be heated to prevent freezing the students and teachers inside and damaging other systems, such as heating coils in the ducts, he said.

Likewise, hot air would have to be cooled, moist air may require dehumidification and any additional volume of incoming air would require new ducts and exchangers to move the same volume out.

'This will take years and years'

The cost of these upgrades would be considerable, especially since the existing heating, ventilation and air-conditioning infrastructure at the Winnipeg School Division's 86 facilities was already listed in poor to fair condition in 2018, when Rendulic completed an infrastructure study. 

That study pegged the average age of a WSD air-handling unit at 44 years, while the devices were intended to last 30. The document estimated the cost of ventilation upgrades at $55 million, just to meet pre-pandemic standards.

Upgrading schools to meet pandemic standards would not just incur equipment and construction costs. Each school's heating and ventilation system would have to be assessed by a mechanical engineer and require its own design, said Rendulic, an electrical engineer by training.

"This will take years and year and years, depending on how many buildings you have to deal with," he said.

The province is aware this challenge cannot be met prior to Sept. 8.

"As far as changes on the fly to create new ventilation systems in schools, it's not possible to do that in the next three weeks, and I think everybody understands that," Premier Brian Pallister said during a media briefing on Wednesday. "We're working very diligently with the resources we have."

The installation of high-efficiency particle filters in schools make make a ventilation upgrade even more expensive and complicated. For every filter you install in a building, more force is required to push air through that filter, Rendulic explained.

That means without more powerful motors, the highest-efficiency air filter would have no greater effect on classroom safety than, say, a cardboard box.

Of masks and two-metre distancing

To Halayko, the respiratory illness expert, improving ventilation is a far less effective strategy for keeping students safe than keeping them apart and requiring them to wear masks.

"It's certainly not going to be the most effective way of mitigating droplets transfer between people. I think that is distancing and, really importantly, the masks," he said.

And make no mistake, even young kids carry the virus that causes COVID-19.

"It looks like kids can carry as much virus in the respiratory tract as what adults can, if not more, in younger age groups" said Kindrachuk, the epidemiologist, adding recent research suggests a greater proportion of kids who do get sick wind up very sick.

"About a third of those cases of kids that were hospitalized ended up in the ICU," he said. "So when kids get infected, we can't think about this from the auspice of them being asymptomatic carriers and not showing signs of symptoms.

"We are actually seeing signs of disease in kids and in some cases quite severe disease."