No need to invest in mechanical ventilation, argues an expert

No need to invest in mechanical ventilation, argues an expert

Not only is “ventilation” not the solution to controlling the coronavirus in schools, but it will never replace the mask, believes an expert engineer in the field.

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On Friday, Education Minister Jean-François Roberge announced that the government will not install air purifiers in classrooms despite the insistence of the opposition and some health experts.

In addition, he indicated that the ventilation of the majority of the classes was sufficient. More than half of the schools (1870 out of 3227) do not have a mechanical ventilation system, having been built before the current standards were put in place.

“In industrial ventilation, we tend to capture contaminants at the source, for example at a welding station, rather than ventilating the entire plant at great expense. In a classroom, these are the people who emit the contaminants, be it CO2, the coronavirus, or the influenza virus. If we want to contain contaminants as much as possible, capture at the source is the famous mask, ”says engineer Patrice Lévesque straight away.

Mr. Lévesque has had his own building mechanical engineering consulting firm since 1992. It now bears the name of NovaMech. He is also the expert for the Corporation des entreprises de treatment de l’air et du froid (CETAF), which brings together nearly 340 companies related to air treatment.

The laws of physics

Noting that today “the majority of stakeholders suggest overventing”, he poses a downside. “How much will we really reduce the risks (of contagion)? There is no one who can tell at the moment. ”

While a modern ventilation system can provide gains in energy efficiency and humidity control, its effectiveness against the spread of the coronavirus is more questionable.

“As the droplets are heavier (than air) they do not tend to go to the grilles on the ceiling. It is for this reason that in an operating room, the evacuation of contaminated air is carried out through grilles at floor level. But this system is unthinkable in schools and offices, ”he says.

The fact that air is sucked in with much less force than it is expelled is also a problem. To convince, Patrice Lévesque suggests a simple test. Stretch her arm and blow air until you can feel it on her hand. Then, while inhaling, bring your hand closer to his mouth until you feel the draft again.

“The difference is obvious. You have to have your hand close to your mouth to feel the air while inhaling. You can do the same test with a flame and a shop sweeper. ”


For these reasons, he has doubts about several of the methods mentioned. Ultraviolet, for example, is very effective in killing the coronavirus, but much less in a ventilation system. The droplets carrying the virus that would go to the ventilation grids, would not go much further according to him.

“It’s a sword strike in the water. We have so little chance that the virus will get to the filter and the ultraviolet system, we pay almost for nothing, ”he says.

High efficiency HEPA filters also cannot defeat the laws of physics. “A portable filter will only pick up what is within a few inches of it. To really process a class, it would take 10. It’s unthinkable, ”he says.

There are also non-ozone ionizers which send air to the ceiling and kill viruses. “It works, but is it worth it?” We won’t be able to process all the air. ”

And however effective the ventilation system may be, the engineer also insists on the need to maintain it, shortcomings at this level are “probably at the source of certain contamination in hospitals” in the past.

The lack of a mechanical system does not mean that school builders did not provide ventilation. Older processes used static or motorized rooftop fans to remove air from the hallways. Hence the presence of windows between the classrooms and the corridors.

“It worked very well. Today, we no longer have the right to build buildings like that, but we will achieve the same result. Ventilation through the windows, when done properly, will provide the required percentages of fresh air, ”analyzes Mr. Lévesque.

Capital factor

From the point of view of protection against viruses, this natural ventilation would have only one shortcoming, that of maintaining a good level of humidity on which he insists a lot. But this problem is easily corrected with the use of a humidifier.

“In a course, I use a chart from the WHO (World Health Organization) that states that the lungs are more susceptible to viruses and disease when the humidity in an environment is below 30% or above 70 %. Regardless of the humidity of the outside air, it will drop once it warms up to decrease to 10 or 15%, ”he explains.

Scientists, in particular with the 40-60RH petition, have also asked the WHO to recommend maintaining the humidity between 40 and 60% indoors to fight against the coronavirus.

The joint work of the German TROPOS and Indian CSIR institute, which included 10 studies on the question, arrived at the same recommendations.

Too expensive and risky

Patrice Lévesque even fears that adding a mechanical ventilation system to schools that do not have one will have a perverse effect.

“No matter how elaborate a ventilation system is, it will be a false sense of security and everyone will take off the masks.” Mechanical ventilation “is not a miracle cure. If it is poorly managed, the relative humidity will drop and amplify the problem, ”he believes.

“This is the future for the next few years, the mask. Basically, capture at source is what works, ”he continues, insisting however on the use of efficient masks.

“In any case, we do not have enough contractors or consulting engineering firms in Quebec to do all this work in schools. We are already rolling the bottom. Is it worth the cost of doing all of this work? Especially for a contaminant that could be treated by opening windows and wearing the mask? The answer is definitely no! ”Concludes Patrice Lévesque.

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