During these months, someone may have begun to consider the purchase of an air purifier (or purifier) as a tool to reduce the chances of contagion, given that – like the viruses of many other infectious diseases – the coronavirus is more easily transmitted. in closed offices or apartments (it is one of the reasons why you get sick more in winter). For those who belong to this category or know a member of it, we have put together a series of useful information.
A necessary premise
Before any consideration on purifiers, the most important thing to know is that even the most effective air exchange and cleaning systems do not it can replace the main prevention measures to reduce the risk of contagion, that is physical distancing and the use of the mask. SARS-CoV-2, the coronavirus that causes COVID-19, in fact is transmitted from one person to another mainly through contact with saliva droplets and not through the air (let's go back).
In general, then, most experts argue that to clean the air in the rooms we live in there are several actions that can be done at no cost with much greater effectiveness than that of a purifier: one of these is opening the windows. as often as possible, at least 2 or 3 times a day for at least 5 minutes, but even more these days. Opening the windows is always recommended because it is proven that the air we breathe in closed places is much more “polluted” than that outdoors (even in cities), and that letting in air from the outside helps dilute the concentration of particles harmful inside.
In the case of the coronavirus, to have the air as “clean” as possible, the first thing to do is to minimize the number of people who breathe in it, and make sure that they wear their masks, do not sing, do not speak loudly. voice and do not do other actions that involve the dispersion of droplets of saliva. In the words of Boston University epidemiologist Eleanor Murray: “An air purifier will never be as effective as simply avoiding having a group of people in the same place.” In short, if you are organizing a dinner with guests in your home, the purifier will not help you.
Coronavirus in the air
SARS-CoV-2 is transmitted via the droplets of saliva we produce when we speak loudly, sing, cough or have one sneeze. The larger and heavier drops (droplets) remain suspended in the air for a short time and then settle on the surfaces. Smaller droplets, on the other hand, can remain suspended in the air for longer (aerosol), reaching greater distances. For this reason, the World Health Organization does not exclude that in particular conditions of humidity and poor air exchange the coronavirus can be transmitted by air.
In any case, the role of room ventilation in the spread of the disease has not yet been fully clarified. Angela Rasmussen, a virologist at Columbia University in New York, told Vox that “there is no totally” safe “level of ventilation, because we don't really know what is” safe “since we don't know how much exposure to the virus is needed because contagion occurs “.
– Read also: WHO and the transmission of coronavirus in the air
What purifiers can do
The components present in the air that have the greatest impact on the health of living beings are VOCs (volatile organic compounds, chemical compounds precisely characterized from their volatility) and PM (particulate matter, or substances suspended in the air with a diameter of up to half a millimeter, produced both from natural sources such as pollen, and from artificial sources such as industries, heating or traffic), fine and ultra-fine. The main requirement for a purifier to be able to clean the air from these particles is that they have advanced filters, which have received a certification from a third public scientific body, Italian or foreign: HEPA filters (from English High Efficiency Particulate Air filter).
HEPA filters are present inside the most effective purifiers and have already been used for some time in the ventilation systems of hospitals and airplanes, where the recirculation of the same air is inevitable during the phases of flight. They cannot do much for VOCs (which despite the initials have nothing to do with the name “COVID-19”, we underline it for the sake of scruple), but they retain fine and ultrafine PM. Joseph Allen, director of a Harvard University center that studies health risks inside buildings, told the Washington Post: “The science is clear. Portable devices with highly efficient HEPA filters and sized to fit the size of the room can capture up to 99.97 percent of air particles “.
It has never been shown that purifiers can prevent respiratory diseases, but they are considered useful for those who already have problems of this kind: those allergic to pollen, dust mites and mold, which are composed of PM. In fact, looking quickly online at the presentations that purifier manufacturers make of their products, we see that the main recipients are above all people who suffer from allergies.
– Read also: There is a problem with the COVID-19 vaccine: the thieves
Other circumstances in which a purifier can be useful are those in which you have to spend a lot of time in a closed environment without windows or in any case difficult to ventilate: this is why HEPA filters are used in airplanes. Obviously in these cases it is necessary to take into account the size of the room and the characteristics of the purifiers to understand which is the most suitable and how long it should be kept in operation. Without going into too many details, the air exchange should be taken into account, which in the case of a purifier depends on the emission rate of clean air, which can be found indicated in the specifications with the acronym CADR, which stands for clean air delivery. installments. The higher it is, the faster the purifier will filter the air into the room, but never like an open window.
And is the coronavirus retained or not?
Yes, in the sense that the SARS-CoV-2 virus is approximately 0.125 microns in diameter and HEPA filters can capture particles of even much smaller size: down to 0.01 microns. And «once trapped», explains an article by Altroconsumo last March, «viruses cannot multiply on their own or remain contagious for long». However, to date there is not enough solid scientific evidence to support HEPA filters alone play a role in preventing the spread of infectious diseases.
So is a purifier useful?
“My main concern with these ventilation systems (air purifiers, ed) is that we don't know if they reduce the risk substantially, ”Muge Cevik, a physician and virologist at the University of St. Andrews, told Vox. According to Tim Heffernan, who has been writing about purifiers in Wirecutter – the influential New York Times item review site – since 2015, “it's possible that HEPA cleaners will only be marginally useful in the coronavirus war.” Experts from the Dyson brand, which has just released a new air purifier, said that “there is currently no manufacturer in the world who can say with certainty that their purifier will help reduce the spread of the coronavirus.”
Altroconsumo's conclusion is that “a HEPA purifier won't hurt, but probably won't help” and that “an open window will probably clear out the room better than any air purifier.” There are also those who think purifiers can be useful – Jose-Luis Jimenez, professor of chemistry at the University of Colorado Boulder, pointed out to Vox that the operation of HEPA filters “is not astrophysics. If you let the air pass through a filter, it retains the particles “- but in conclusion we can say that, especially in the case of domestic use, there are no great advantages in the field of contagion prevention.
Anyone wishing to buy a purifier in this period should remember that HEPA filters retain the virus but do not kill it, and when cleaning them you must be careful: use gloves and a mask, put the filter in a bag, immediately throw it in the garbage can. and wash your hands after doing so.
– Read also: What went wrong with the flu shot
