During the covid-19 pandemic, it appeared to the scientists that the level of CO2 in a room is strongly correlated with the spread of coronavirus by air. Based on this observation, they now suggest that a CO2 monitor be installed to slow down the spread of Omnicron and its many variants.
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Measuring with a CO2 sensorCarbon dioxide is a gas that is naturally generated when we breathe. Each person in a room exhales an average of eight litres of air per minute. This air consists of tiny droplets of liquid which, because of their size, are likely to remain suspended in the air for some time. The problem is that these droplets (aerosols) are conducive to the transmission of the coronavirus in the presence of a sick person.
There is a consensus that the fall rate of these aerosols is typically a few metres per hour and that the decrease in biological activity of viral infection has a half-life of about three hours under laboratory conditions. In other words, this means that indoor air can remain polluted for a long time after contamination. Thus, if a healthy person inhales these droplets in sufficient quantity to achieve a minimal infectious dose, the disease is transmitted.
To date, it is not possible to measure the viral load in the air directly, but both CO2 sensors and air quality sensors are the ideal solution to compensate for this problem. By monitoring the concentration of CO2, we are able to change the air in a room at the right time, allowing us to dilute the contaminants and aerosols in the air and reduce the exposure of the people inside.
A 2019 study of a tuberculosis outbreak at Taipei University (Taiwan) found a correlation between the concentration of CO2 and the rate of transmission of the virus in the air. At the start of the outbreak, many rooms were not properly ventilated and some reached CO2 levels of over 3000 ppm. It was only when engineers reduced the levels to below 600 ppm that they were able to reduce the risk of exposure to the virus and thus stop the outbreak.
The level of CO2 in a room is proportional to the number of people in the room, the length of time the room is occupied and the ventilation of the room. If you are confined to a poorly ventilated room for a long period of time, you run a high risk of inoculating yourself with coronavirus. Keeping you away from other people may not be enough, as the air moves.
But why measure CO2? Theoretically, the mass balance of air in a room indicates that a CO2 concentration of about 1200 ppm is equivalent to 2 % of that air already having been breathed in at least once. At this level, every 50 ᵉ inhalation of a person is therefore air that has already been exhaled. Therefore, as the level of CO2 in the air increases, so does the risk of inhaling an infectious dose sufficient to infect us.
In the video above, according to Florence Elias, a professor of physics at the University of Paris, we see that
Masks trap droplets when we exhale air and protect when you breathe. If everyone is wearing one, the ideal is not to exceed 800 to 1000 ppm in the room. In places without masks, such as canteens, the consensus is not to exceed 600 ppm.
Intervention by F. Elias from 25:26
The level of CO2 depends on whether or not the mask is worn, the number of people and the configuration of the premises. When faced with covid, we advise you to air the room as soon as the CO2 level in the air is between 600 and 800 ppm. Ventilating the indoor air at the right time is essential if you want to reduce the risk of coronavirus contamination.