Washing masks doesn’t affect their ability to filter viral particles: Study

The study, published in the journal Aerosol and Air Quality Research, also confirms previous research showing that layering a cotton mask over a surgical mask that fits snugly over one’s face provides more protection than cloth alone.

“This is good news for sustainability,” said lead author Marina Vance, author of Mechanical Engineering’s Paul M. Assistant Professor in Ready Department. “That cotton mask you’re washing, drying, and reusing? It’s probably still fine—don’t throw it away.”

science for sustainability

Since the start of the pandemic, an estimated 7,200 tonnes of medical waste has been generated every day – most of which are disposable masks.

“We were really upset during the start of the pandemic when going out on a hike or going to town, and seeing all these disposable masks littering the environment,” said Vance, who is faculty in the environmental engineering program. are also in

So Vance was eager to join forces when scientists from the nearby National Renewable Energy Laboratory (NREL) approached him to study how washing and drying affected reusable cloth masks.

Their process was fairly simple: Make two-layer squares of cotton, put them through repeated washing and drying (up to 52 times, the equivalent of washing weekly for a year) and test them approximately every 7 cleaning cycles. .

While the masks weren’t tested using real people—instead, they were mounted on one end of a steel funnel, through which researchers could control a continuous flow of air and airborne particles—the researchers created real-life Tested the mask using realistic to conditions. With higher humidity levels and temperatures, to mimic the effect on masks from our breathing.

While the cotton fibers began to break down after repeated washing and drying, the researchers found that this did not significantly affect the filtration efficiency of the fabric.

The only noticeable change was that the inhalation resistance was slightly increased, meaning that after some wear and tear the mask might find it a bit difficult to breathe.

Mask fit is important

One important caveat is that they tested using a “perfect fit” in the lab.

“We are assuming there is no gap between the mask material and the person’s face,” Vance said.

The shape of each person’s face varies greatly. So depending on the size of a mask and how well the person adjusts to it, it may or may not fit properly. Previous research has shown that a poorly fitted mask can allow up to 50 percent of airborne particles in and out, as well as viruses.

So which mask should you wear?

This study is not the first to show that cloth masks provide less protection than surgical masks or a layered combination of surgical and cloth masks.

To measure how well the mask is breathing air – protecting the person wearing the mask, not reducing transmission from the source – this study found that cotton cloth masks had the smallest particle size (0.3) filter up to 23 percent. micron) on which the virus can travel. Bandanas filter even less, at only 9 percent.

In comparison, surgical masks filtered out between 42-88 percent of smaller particles, and cotton masks achieved near 40 percent filtration efficiency over surgical masks. The KN95 and N95 masks performed surprisingly best, filtering out 83–99 percent of these particles.

But while this study found that only cloth masks offer less protection from the virus than a layered approach or disposable masks, such as surgical masks, KN95s and N95s, it is important information for those who care about its comfort, affordability and depend on the fabric for reusability. Vance said.

“I think the best mask might be the one you’re actually going to wear,” Vance said. “And it’s going to fit snugly over your face without being too uncomfortable.”

Additional authors for this publication include Sumit Sankhyan, Samir Patel and Hannah Teed of the University of Colorado Boulder; Karen N. of the Center for Renewable Resources and Enabling Science at the National Renewable Energy Laboratory. Henselman, Peter N. Sisilsky Teresa Barnes and Michael E. Himel.