Tech study: Facemasks protect wearers and others about the same
Face masks are about as effective at protecting the wearer from COVID-19 exposure as they are at protecting others, according to a new study by Virginia Tech researchers.
Masks were originally advertised to reduce the amount of virus a person exhaled, noted Linsey Marr, a professor of civil and environmental engineering and the study’s lead author.
“If I’m sick, you know, I put on the mask and then it reduces the amount that I released into the air around me,” Marr said Monday. “It turns out masks work essentially the same way and offer very similar protections to the wearer.”
Marr’s niche expertise in the airborne transmission of viruses brought her international attention back in the spring as evidence mounted that COVID-19 spreads through tiny droplets exhaled from the nose and mouth.
Marr’s team first began studying cloth masks in March, when N-95 masks were in short supply and health officials called on the public to make their own face coverings.
“I realized it would be really important for the general public to wear masks because of presymptomatic or asymptomatic transmission” of the virus, she said. “It was up to the public to make their own cloth masks.”
The team tested 10 different kinds of face mask materials — including a microfiber used for cleaning eyeglasses, a thick bandana, a kid’s T-shirt and a pillow case — as well as a plastic face shield.
Manikin heads were fitted with the face coverings. Researchers used a misting machine and a vacuum machine on two different heads to simulate breathing in and exhaling. They then calculated how many various-sized particles from a salt spray were blocked by the masks.
Most of the fabrics could block at least 50% of particles the size of two microns — a rough estimate of a respiratory droplet coming out of amasked mouth — with a vacuum bag, microfiber cloth and surgical mask nearing 90% efficacy.
Researchers also tested two versions of homemade masks recommended by the U.S. Centers for Disease Control and Prevention. They used a 200-thread-count pillowcase and rubber bands for the non-sewn version and a cotton Tshirt for a sewn mask.
While these homemade masks were not as effective at stopping particles less than one micron, they achieved about 50% efficacy for two-micron particles and 75% efficacy for particles greater than five microns (a human red blood cell is about seven microns in size).
“One criticism of masks is, ‘Oh, they don’t work,’” Marr said. “It’s not N-95 or bust.”
Cloth masks, in addition to physical distancing, good ventilation and handwashing, can reduce the risk of contracting and spreading the virus.
“Anything we can do to reduce that is going to be helpful,” Marr said.
The face shield fared the worse by far, based on the results of the study, which has not yet been peer-reviewed.
Based on the findings, the team recommends people wear a three-layer mask, consisting of outer layers of tightly woven fabric with an inside layer of a material designed for filtration, such as a vacuum bag or air filter.
That combination should result in an efficiency of 70% for the most penetrating particle size and more than 90% for particles larger than one micron, if the mask fits well, the study found.