Air rather than surfaces. One year after the first confinement during which the disinfection of shopping baskets was a source of anxiety, scientists insist on the role of airborne contamination, via aerosols, that is to say fine droplets which remain suspended in the air for a longer time, allowing their transport over greater distances.
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“The media breakthrough on this issue of airborne contamination is recent, with several publications in the most prominent journals, but work had started last year”, recalls Bruno Andreotti, professor of physics at the University of Paris, who issued recommendations for a secure reopening of shopping centers.
Measure and assess risk factors
Proof of this interest, the Massachusetts Institute of Technology (MIT) presented a tool to calculate the risks of contamination in confined spaces according to different factors: wearing of the mask, activity (singing, speaking), surface area of the room, ventilation, rate of people infected or variant of the virus.
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“A rather reliable tool”, comments Bruno Andreotti, who suggests quantifying the risks for each situation. In terms of dangerousness, a party in a poorly ventilated private home remains particularly discouraged, while establishments receiving masked public (cinemas, museums, businesses) can be secured relatively easily: ” For cinema, including an FFP2 mask in the ticket price would have solved the difficulties “, Believes Bruno Andreotti. The most serious challenge is on the side of ” canteens and restaurants, where one is deprived of the protective effect of the mask: one can install “Covid vacuum cleaners” for each table and purifiers in quantity, but on the condition of substantial investments “.
Singing, the “most contaminating activity”
In addition to the characteristics of the place, the activity performed and its duration are essential to assess the risks: choirs were, in 2020, among the events ” super propagators », Because singing considerably multiplies the particles emitted. ” It is the most contaminating activity there is », Insists Bruno Andreotti.
Thus, in July 2020, a chorister from a parish in Sydney, positive for Covid-19, sang during four masses of one hour each, contaminating a series of faithful, some of whom were however seated … at about fifteen meters . “ The fact that the jet of viral particles could have passed over the heads of the closest spectators demonstrates the transmission by aerosol: it was not a postilion who touched the infected. An aggravating factor, the ventilation of the church was not working and doors and windows were closed.
So is it risky to sing in a church? ” We must distinguish two sources of risk », Answers Bruno Andreotti:« One, at close range, is related to the distance necessary for the breath to dilute in the surrounding air. », Which can be resolved by the distancing measures currently adopted in places of worship. Combined with the wearing of a mask, the provisions sufficiently limit the danger to singing.
Good use of stained glass and incense
However, remain ” the other risk, of long range, which depends on the storage of viral particles in the available space He continues. With a larger volume than other public places, one might think that churches have an advantage, but this is partial: ” A large space is also more difficult to ventilate “, Says the researcher. The particles accumulate and the air must be renewed.
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How? ‘Or’ What ? By ensuring the circulation of air between the main door and the choir: “ The through air currents are essential to reduce the risks: if part of the stained glass is removable, this solution must be seized. “And, to assess the quality of the aeration, the censer is an ideal tool:” Frankincense smoke is exactly the size of viral particles: if the place is well ventilated, it evacuates quickly, otherwise it will stagnate for several tens of minutes and the smell will float », Indicates Bruno Andreotti. Who pleads, in favor of fine weather, for ” organizing as many outdoor activities as possible “.