Without a mandatory mask, how can you protect yourself from covid in public places?

Wearing a mask is no longer compulsory in establishments open to the public, with the exception of all indoor transport and in places of health or care. However, with a reproduction rate R greater than 1, the epidemic is not declining at the start of spring 2022. Contaminations remain well above the vigilance threshold with more than 100,000 daily cases.

And with an incidence rate of more than 1,000 per 100,000, clusters emerge at the end of meetings, fairs and other gatherings. This is what happened during the Angoulême Comics Festival where many exhibitors, visitors and journalists caught the coronavirus.

In the absence of being able to impose the mask, what levers can be activated to limit the risk of transmission in closed public places?

Test and isolate

First step, the most logical: if we want to prevent the transmission of covid in an enclosed place, we must prevent the virus from entering these places. It is then a question of continuing to promote the isolation of positive people and that of symptomatic people awaiting a test. Since isolation is not compulsory, it is based on individual responsibility.

For large-scale events, antigen tests could be offered at the entrance for those who wish. Similarly, it would then be a matter of relying on the good will of the participants.

The mask acts against sputters and aerosols

Next, we need to come back to the modes of transmission of the SARS-CoV-2 coronavirus and the role of the mask – this is what will also allow us to better understand the actions that can partially compensate for the absence of masks.

If transmission by surfaces was greatly overestimated for a time, it is now established that covid is transmitted by droplets — that is to say by the sputters, visible, which one emits when one coughs, spits or sneezes; and by aerosols, which are airborne particles with a size of less than 5 microns. As invisible and impalpable as these particles are, it is through them that the majority of contamination occurs.

The role of the mask is both to avoid transmission by these droplets and to limit that by aerosols. The effectiveness of masks in curbing contamination is fully established, the most effective being FFP2, followed by surgical. Thus, nothing prevents a public place or a company from specifying that wearing a mask is recommended.

It is possible to reduce the transmission of covid, even without a mask

It is quite easy to fight against contamination by droplets by respecting barrier gestures, because the sputters quickly fall back to the ground after their emission. Among these actions are:

• Cough or sneeze into your elbow or a tissue.
• Respect physical distancing — at least one meter when possible.

On the other hand, with regard to transmission by aerosols and especially in closed public places where clusters occur, things are a little more complex, but reducing the risks is not impossible there.

Ventilate, ventilate and ventilate again

Ventilation is a key measure. Since aerosols dissolve in air, “ the idea is to ensure sufficient air renewal both by playing on the gauges and by working on the quality of the aeration/ventilation of the premises »explains Jean-Michel Courty, physicist and member of the Project CO2 working group.

To do this, the idea is to be able to measure the carbon dioxide (CO2) level of spaces and act accordingly. to prevent the rate from exceeding 800ppm. As the physicist points out: There are many parameters that prevent common sense from operating in this area. It is therefore difficult to establish generalities, which implies strategies on a case-by-case basis.

For further

Among the various factors that affect the CO2 concentration – and thus the concentration of potentially contaminating aerosols, we note:

• The possibilities of opening windows and doors, and creating drafts.
• Weather. Jean-Michel Courty explains: “ In winter, when the windows are opened, air exchanges are rapid and ventilation is effective. But, from spring, when it is the same temperature outside and inside, air exchange is limited. The windows would then have to be left open at all times. »
• The height of the ceilings allowing more or less the dispersion of aerosols.
• The type of activity of the people present: When we exercise, when we sing, when we shout and even when we talk, we emit more aerosols than when we remain silent and still. “recalls Jean-Michel Courty. Thus a sports hall or a choir class will have to be ventilated more often and longer than a theater or a library.

When it is impossible to open the windows to ventilate properly and lower the CO2 level to an acceptable level, it is advisable to equip yourself with mechanical ventilation equipped with HEPA filters. ” They are high efficiency filters capable of removing small aerosol-sized particles. explains Jean-Michel Courty.

However, these measures do not 100% replace wearing a mask. This constitutes a slice of the “Emmental” of the anti-covid provisions, when aeration-ventilation constitutes another.

If zero risk does not exist, it is however possible to reduce the risk of contamination by closely monitoring the CO2 level of interior spaces and acting accordingly so as not to exceed a rate of more than 800ppm attesting to a renewal. insufficient air.