The performance of a large number of COVID-19 facial masks used in Brazil for breathability and aerosol collection efficiency.

Abstract:

The use of face masks is being mandatory in many countries in order to slow the spread of COVID-19. Brazil was a country that was strongly affected by the Sars-CoV-2 virus pandemic. Due to a lack of easily available surgical masks, the population in general has manufactured masks with different fabrics, grammages and geometries, what impact the filtering efficiency (FE) and breathability. The performance of 285 samples of face masks of 11 different fabrics being used in Brazil was evaluated to quantify the collection efficiency and breathability efficiency of airborne particles. The FE was measured as a function of aerosol particle size from 60 to 300 nm using NaCl particles and a TSI Scanning Mobility Particle Sizer (SMPS). The FE was also evaluated for particles around 100 nm, that is the average size of Sars-Cov-2. Breathability was determined by measuring the differential pressure drop over the mask. Our results showed that, for professional masks such as N95, the FE is a high 98%. For many masks, the breathability quality is below the recommendations of World Health Organization (WHO). Also, surgical masks showed median FE between 86 to 91% and high dispersion on breathability, ranging from 0.1 to 7 mm H₂O/cm². In contrast, cotton masks, the most common found in the marked, have a low filtration efficiency of about 40%, which is way below the value recommended by WHO, and breathability around 4.0 and 6.6 mm H₂O/cm² depending on the number of layers. It was found that many masks in the market have very low FE of 10-20%, which do not properly protect the health and do little in suppress coronavirus transmission. For cotton masks, an additional cotton layer showed an increase in the efficiency, but it impacts in a reduction of the breathability as well. Masks cleaning methods were also tested, and shows that after 5-6 cleaning cycles, most of the masks start to get lower filtration efficiency. No direct correlation was found for filtration efficiency and breathability for hybrid combination with different fabrics, as recommended by WHO, neither with the number of layers nor total grammage for any type of fabric. Some masks using polyester, neoprene, paperboard, and microfiber fabrics showed to be unbreathable and for this reason should be avoided; even though some of them presented high filtration efficiency.