Cloth masks have poor protection from airborne virus spread
of the AIP Publishing House, researchers from the UK, Germany and France focused their expertise and microscopes to test the effectiveness of woven particle filtration.
Woven fabrics, unlike those used in standard air filters and face masks, are composed of fibers that are twisted together into yarn. Therefore, there are two length scales: the diameter of the thread and the thread.
Using 3D images generated by confocal microscopy to view the airflow channels, the scientists simulated the airflow through these channels and calculated the filtration efficiency for particles with micrometers and large diameters. than. The study is conclusive for particles in this size range; low filtration efficiency.
Co-author Richard Sear from the University of Surrey said: “Masks are air filters and woven fabrics, such as cotton, can make up jeans, shirts and other clothing, but They are lousy air filters.” “So use woven fabrics for clothes and N95s or FFP2s or KF94s for masks.”
Indeed, flow simulations show that when a person breathes through the fabric, most of the air flows through the gaps between the fibers in the woven fabric, carrying more than 90% of the particles with it.
“In other words, these relatively large voids are what makes fabric a bad material for making air filters,” says Sear.
“In contrast, the filter layer of an N95 mask is made of much smaller fibers, 5 micrometers with openings ten times smaller, which helps to much better filter unpleasant particles from the air, such as those with contain viruses”.
While previous work showed similar findings, this study represents the first to simulate particles traveling directly through voids in woven fabrics.
The Sear-added fine mask should have “two F’s: good filtering and good fit”.
“The surgical mask doesn’t fit well, so a lot of air gets through the edges of the mask by the cheeks and nose,” says Sear.