Masks: How layers and substances help protect against COVID-19 and other diseases

Double mask

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Atlanta: Wearing a face mask can protect you and others from COVID-19, but the type of material and how many layers of clothing are used can greatly affect the risk of exposure, a new study from Georgia Institute of Technology.

The study measured the filtration efficiency of submicron grains passing through a number of different materials. For comparison, human hair is about 50 microns in diameter while 1 millimeter is 1,000 microns in size.

“Submicron particles can stay in the air for hours and days, depending on the ventilation, so if you have a room that is not ventilated or poorly ventilated, these small particles can stay there for a very long time,” said Nga Lee (Sally) Ng, associate professor and Tanner Faculty Fellow in the School of Chemical and Biomolecular Engineering and the School of Earth and Atmospheric Sciences.

The study was conducted in the spring of 2020 when the pandemic prompted a global closure of most institutions. Communities were facing a severe shortage of personal protective equipment, forcing many people to make their own homemade masks. Georgia Tech quickly set up the study because “there was already a good system for testing the effectiveness of filters using existing laboratory instruments,” recalled Ng.

The findings of the study were used to design home face mask recommendations here in April last year, with extensive study findings published on March 22 in the journal Aerosol Science and Technology.

In total, the researchers tested 33 different commercially accessible materials that were not restricted to clothing fabrics, including single-layer textiles such as cotton and polyester fabrics, blended fabrics, fabrics non-woven, cellulose-based products, materials commonly found and used in hospitals, and various filter materials.

“We learned that there was a lot of variability infiltration performance even in the same type of material,” Ng said.

“We found commercially available materials that provide adequate levels of submicron particle rejection while still maintaining airflow similar to a surgical mask,” said Ryan Lively, associate professor and Fellowship of John H. Woody Faculty of Chemical and Biomolecular Engineering. “These materials combine fabric fiber density, circuit-like structure, and fiber surface chemistry to effectively reject submicron grains.”

The best materials to play for home masks were black cloths and a sterilization blanket widely used for packing surgical instruments. Both products are commercially available.

The researchers said people should avoid filters such as HEPA / MERV or empty bags unless they have been proven fiberglass-free as such filters alone can often release glass fibers. into. Other materials to avoid for masks include loose-knit fabric, batting cloth, fencing, fleece, or reusable glossy shopping bags.

Complex samples performed much better than single-fold samples, but people should pay attention to breathability. The tested two-layer and three-dimensional samples show an overall filtration efficiency of about 50 percent for submicron particles. A mask is also appropriate as grains can easily escape through gaps at the nose or through the sides of the mask.

The analysis showed that properly equipped and multilayer masks repel 84 percent of the grains that a person removes when one wears it. Two browning of these types of masks reduces grain transmission by 96 percent.

The final takeaway of the research was the importance of universal mascara wear.

“The best way to protect ourselves and others is to reduce exhaled grains at the source, and the source is our face,” Ng said, adding, “That will greatly reduce grow bigger when everyone starts wearing masks. “

She expressed hope that the decisions would encourage people to adopt mascara more widely if they are ill and need to be in public.

“Not everyone understands the importance of the spread of airborne viruses, and the importance of wearing a mask,” she said.

She concluded, “I hope the practice will continue by reducing the spread of these viral grains into the environment and helping to protect others.”