Many ventilation systems can increase the risk of exposure to Covid-19, according to a study

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The ventilation systems in

, which are designed to maintain comfortable temperatures and increase energy efficiency,

, particularly during winter, according to research from the University of Cambridge (UK) published in the 'Journal of Fluid Mechanics'.

This team found that mixed ventilation systems, which are designed to

in all parts of the room, disperse air pollutants evenly throughout the space.

These

, which can contain viruses.

Research has highlighted the

and the use of face masks to keep the concentration of contaminants to a minimum and therefore mitigate the risk of transmission of SARS-CoV-2, the virus that causes the disease. Covid.

Evidence increasingly indicates that the virus spreads primarily

, which are expelled by coughing, sneezing, laughing, talking, or breathing.

In addition, the data available to date indicates that

is much more common than outdoor transmission, which is likely due to increased exposure times and decreased dispersion rates of droplets and aerosols. .

"As winter approaches in the Northern Hemisphere and people begin to spend more time indoors, it is essential to understand the role of ventilation in estimating the risk of contracting the virus and

" explains the Professor Paul Linden, Cambridge Department of Applied Mathematics and Theoretical Physics, who led the research.

"Although direct surveillance of droplets and aerosols in indoor spaces is difficult, we exhale carbon dioxide which can be easily measured and used as an indicator of infection risk. The small respiratory aerosols containing the virus are

, and are carried through a room by ventilation flows. Insufficient ventilation can lead to a high concentration of carbon dioxide, which in turn could increase the risk of exposure to the virus, "he adds.

Air flows

The team showed that airflow in rooms is complex and depends on the

, and on the convection flows generated by the heat emitted by people and equipment in a building.

Other variables, such as people moving or talking, the opening or closing of doors, or

naturally ventilated

, affect these flows and therefore influence the risk of exposure to air. virus.

Ventilation, whether driven by wind or heat generated inside the building or by mechanical systems, works in one of two main modes.

Mixed ventilation is the most common, in which vents are placed to

so that the temperature and concentrations of pollutants remain uniform throughout the space.

The second mode, displacement ventilation, has vents placed at the bottom and top of a room, creating a cooler lower zone and a warmer upper zone, and hot air is drawn through the upper part of the room. .

Since our exhaled breath is also hot, most of it collects in the upper zone.

As long as the interface between the zones is high enough, the polluted air can be drawn through the ventilation system instead of being breathed in by someone else.

The study suggests that when properly designed,

of mixing and cross-contamination of the breath, thus mitigating the risk of exposure.

The researchers explored a range of different modes of exhalation: nasal breathing, speaking and laughing, each with and without a mask.

By visualizing the heat associated with exhaled breath, they were able to see how it moves through space in each case.

, the distribution of the exhaled breath was markedly different when captured in its path.

"You can see the change in temperature and density when someone breathes out hot air: it refracts light and you can measure it. When you're sitting, humans give off heat, and as hot air rises, when you exhale, your breath rises and it accumulates near the ceiling, "they detail.

Their results show that

and can change dramatically depending on the movement of the occupants, the type of ventilation, the opening and closing of the doors and, in the case of naturally ventilated spaces, changes in outside conditions.

The researchers found that the masks are effective in reducing the spread of exhaled breath, and thus droplets.

Mask effectiveness

"One thing we could clearly see is that one of the ways that masks work is by stopping the impulse of breathing. Although almost all masks will have a certain amount of leakage through the top and sides, it doesn't matter that much. , because slowing down the impulse of any exhaled pollutant

direct

of aerosols and droplets, as the breath remains in the body's thermal plume and is carried upward toward the ceiling. In addition, larger droplets are stopped, and a three-layer mask reduces the amount of these pollutants that are recirculated through the room by ventilation, "they say.

The researchers found that laughing, in particular, creates a great deal of disturbance, suggesting that if an infected person without a mask were to laugh indoors, it would greatly increase the risk of transmission.

"

seems like the best advice. Clearly that is less of a problem in the summer months, but it is cause for concern in the winter months," they conclude.

According to the criteria of The Trust Project

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