A study, conducted by the Georgia Institute of Technology, has found that type of material and how many fabric layers used can significantly affect the exposure risk of the Covid virus.
The filtration efficiency of submicron particles passing through a variety of different materials was measured by the study. For comparison, a human hair is about 50 microns in diameter while 1 millimeter is 1,000 microns in size.
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 said, “A submicron particle 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 then these small particles can stay there for a very long period of time.”
The study was conducted during spring 2020 when the pandemic triggered a global shutdown of most institutions. Communities faced massive shortages of personal protective equipment, prompting many people to make their own homemade masks. Georgia Tech quickly set up the study since it already had “a great system for testing filtration efficiency using existing instruments in the lab,” Ng recalled.
With the comprehensive study findings published on March 22 in the journal Aerosol Science and Technology, the study’s findings were used to shape homemade face mask recommendations here in April last year.
The researchers tested 33 different commercially accessible materials not limited to cloth fabrics that included single-layer woven fabrics like cotton and woven polyester, blended fabrics, nonwoven materials, cellulose-based materials, materials commonly found and used in hospitals, and various filter materials.
“We learned there was a lot of variability infiltration performance even in the same type of material,” Ng said.
Ryan Lively, an associate professor, and John H said, “We found commercially available materials that provide acceptable levels of submicron particle rejection while still maintaining airflow resistance similar to a surgical mask.”
Woody Faculty Fellow in the School of Chemical and Biomolecular Engineering. “These materials combine fabric fiber density, a maze-like structure, and fiber surface chemistry to effectively reject submicron particles.”
The best-performing materials for homemade masks were blackout drapery and sterilization wrap widely used for packing surgical instruments and both materials are commercially accessible.
Other materials to avoid for masks comprise loose-knitted material, batting fabric, felt, fleece, or shiny, reusable shopping bags. However, according to researchers’ people should avoid using filters like HEPA/MERV or vacuum bags unless they are certified to be fiberglass-free since often such filters on their own may release glass fibers that can be inhaled.
Mask fit equally important since the particles can easily leak through the gaps at the nose or through the sides of the mask.
There are multilayered samples that performed much better than single-layer samples but at the same time, people need to pay attention to breathability. However, overall filtration efficiency of about 50 percent for submicron particles was tested in the two-layered and three-layered samples.
A final takeaway from the research was the importance of universal mask-wearing.
An analysis found that properly fitted and multilayer masks rejected 84 percent of particles excluded by a person when one person wears it and two people wearing these types of masks reduces the particle transmission by 96 percent.
“The best way to protect ourselves and others is to reduce exhaled particles at the source, and the source is our face,” Ng said, adding, “That really gets amplified when everyone starts wearing masks.”
She expressed optimism that the findings will motivate people to more widely embrace mask-wearing if they are sick and need to be in public.
“Not everyone understands the importance of airborne virus transmission, and the importance of wearing a mask,” she said.
She concluded, “I hope that the practice will continue to help reduce the release of these viral particles into the environment and help protect others.”
