To cope with the epidemic resumption, several braking measures are in force, including the strengthening of barrier gestures. Can you remind us of these essential gestures?
There is, of course, the fact of maintain a physical distance of at least two meters with our interlocutors in order to avoid, but we will come back to this, the postilions who can project themselves up to a distance of two meters and who can be contaminants if they fall on, in particular, the mouth, the nose or the eyes.
There is, of course, wearing a mask which is really important in confined spaces, and outdoors in really dense population areas.
Hand hygiene and the importance of washing hands is also part of the barrier gestures. Because the hands may have touched surfaces contaminated by postilions. It is therefore also important to clean the surfaces in addition to the hands. This is also why we should not shake hands.
When we cough or sneeze, we have to cover our nose or mouth with the bend of the elbow. And, if a tissue is used, it must be disposable and discarded after use.
Finally, there is the ventilation concept.
Can you explain to us how ventilation is particularly effective in reducing the risk of SARS-CoV2 transmission?
With this respiratory virus, it was understood that aerosols contribute to the transmission of the virus whereas initially it was thought that the postilions or contaminated surfaces were the most important vectors.
Aerosols are very fine particles (less than 5 microns in diameter) which, in fact, can remain suspended in the air.
The concentration of virus in the throat with SARS-CoV2 is so great that, even while speaking, one can emit aerosols which contain infecting virus, remain in suspension and can be diffused up to several meters in the room.. It then becomes very important to ventilate the room to dilute these aerosols and their concentration, and thus prevent them from contaminating someone else.
“You can become infected from a distance via aerosols because they remain suspended in the air due to their very small size. “
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How to define, in a pictorial way, the aerosols, responsible for the transmission of the virus?
Imagine the cigarette smoke spreading, it gives you an idea of the volume that can be covered by the aerosols!
What is the difference between droplets and aerosols?
All particles are droplets, but there are:
- micro-droplets or aerosols with a diameter of less than 5 microns;
- other droplets, in particular postilions, the diameter of which is greater than 100 microns.
Because the postilions have a large diameter, they fall to the ground. Because aerosols are small, they stay suspended in the air. And, the louder you speak, the more aerosols you emit.
How long do aerosols stay suspended in the air?
It is difficult to have a precise quantification, but we consider that aerosols can remain suspended in the air for several hours.
How to ventilate well?
Aeration consists, when you are in a room, of open windows for 10 minutes every hour. It is with this frequency that we arrive at have a significant impact on the aerosol concentration potentially infected in the air.
Obviously, these recommendations can change depending on the number of people in the room, the size of the latter …
On a very large volume, for example, the aerosol concentrations will be lower; if you are in a narrow room, the concentrations rise very quickly and you have to open the windows to dilute them.
What does ventilation allow in practice, and how can it be controlled?
We ventilate to dilute the aerosols. To find out if the air renewal is sufficient, the CO2 concentration is measured.
- In outdoor air, it is of the order of 400 ppm (parts per million).
- When we find ourselves in a room, the concentration rises and the acceptable threshold is established at 800 ppm.
- On the other hand, if you are in a room where you have to remove your mask, such as a cafeteria, for example, 600 ppm is a preferable threshold.
With a CO2 sensor in a room, it is easy to calibrate the aeration frequency to maintain a CO2 level at acceptable levels.
If ventilation is not possible, is there an alternative solution?
In closed environments, when ventilation is not possible, there are ventilation systems or mobile air purification units by HEPA filtration which, when properly positioned, allow the removal of aerosols.
In terms of contamination, what are the most risky places?
These are the closed, unventilated places where people are talking loudly, singing or shouting.
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