The transmission of the new coronavirus mainly occurs by inhaling saliva droplets and respiratory secretions suspended in the air, which is why wearing masks and keeping a social distance are the most effective way to prevent Covid-19 while there is no vaccine for everyone.
Masks, made of cloth, are inexpensive, reusable, and available in a variety of colors and prints are among the most commonly used by Brazilians. However, its ability to filter aerosol particles of equivalent size to the novel coronavirus can vary between 15% and 70%, as revealed by a study conducted at the University of Sao Paulo Institute of Physics (IF-USP).
Coordinated by the teacher Paulo Artaxo e Supported By FAPESP, action is part of the initiative (Same!, Whose goal is to ensure access to safe masks for the Uspian community. The results are reveal In Revista Aerosol Science and Technology.
“We evaluated the filtration efficiency of 227 models sold in Brazil, both in pharmacies and in popular stores. Our goal was to find out to what extent the population is being protected with these different masks,” Artaxo tells Agência FAPESP.
To perform the test, the scientists used equipment that produces, from a sodium chloride solution, aerosol particles of controlled volume – in this case 100 nm (Sars-CoV-2 is about 120 nm). After the aerosol jet was released into the air, the particle concentration before and after the mask was measured.
The models that proved most effective in testing, as expected, were the surgical masks and the PFF2 / N95 type – for both professional and certified use – which managed to filter between 90% and 98% of the aerosol particles. Below is TNT (made of polypropylene, a type of plastic) sold in pharmacies, its efficiency ranges from 80% to 90%. Finally came the fabrics – a collection that includes models made from cotton and synthetic materials, such as lycra and microfibre. In this case, the filtration efficiency ranged between 15% and 70%, with an average of 40%. Certain factors have been shown to be crucial in increasing or decreasing the degree of protection.
“Generally, masks with seams in the center provide less protection, as the machine punches holes in the fabric that increase the airflow. Having a nose clip that helps hold the mask to the face greatly increases filtration, due to a better fit of the face. Some fabric masks made of mineral fibers inhibit virus activity, such as nickel or copper, and thus protect more. There are also models of materials that are electrically charged, which increases particle trapping. However, in all these cases, the efficiency decreases with washing, due to the presence of corrosion The materials, “comments Fernando Moraes, PhD student at IF-USP and the Institute for Energy and Nuclear Research (Ipen), who is the first author of the article.
Inhale and exhale
According to Artaxo, the two-layer cotton masks filtered far more spray particles than those made with just one. But from the third tier onwards, the efficiency increased slightly, while the ventilation was significantly reduced.
Among the novelties in the study was the evaluation of the breathability of masks, that is, the material’s resistance to the passage of air. TNT and cotton were the best in this regard. The PFF2 / N95 ones weren’t very comfortable. But the worst was made of paper. This is an important aspect, because if a person cannot stand up to five minutes with the mask, then it is not helpful, ”says Artaxo.
As the authors point out in the article, although efficiency varies, all masks help limit the spread of the new coronavirus and its use – linked to social disconnection – is essential to controlling the epidemic. They also state that the ideal is the mass production of PFF2 / N95 masks for free distribution to the population – something that “must be taken into account in future epidemics,” in the evaluation of Vanderley John, Coordinator of the (Breathe!) Initiative, organized by the Innovation Agency of the University of the South Pacific, and co-author of the study.
“Today it is already proven that the main form of pollution is through the air and wearing masks all the time is one of the best prevention strategies, so keeping windows and doors open to ventilate environments as much as possible,” Artaxo recommends.
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