Counties and cities around Colorado have started requiring residents to wear face coverings. In Denver, masks became necessary on Wednesday. Boulder’s rule takes effect Saturday. Larimer County has required masks since Monday.
N95 masks are the only ones proven to prevent transmission of the virus. But they are also the hardest to obtain right now, and officials are urging the public to save the country’s limited supply of personal protective equipment for front line medical workers. Most people don’t have access to even regular medical grade masks. They’re improvising with bandanas or sewing their own out of cloth with patterns available online.
Homemade cloth masks are not up the same standards as medical grade masks. So why are cities and counties requiring them?
John Zhai, a professor of buildings systems engineering at the University of Colorado Boulder, says that wearing even a homemade cloth mask decreases the potential transmission of COVID-19. He walked us through the rationale behind the face covering requirements, and shared some best practices when it comes to wearing them.
Why should we wear masks?
Zhai says it’s true that there is no quality control when it comes to homemade face coverings, like there would be for medical grade masks. But those cloth face coverings are still much better than nothing.
The virus is spread largely through droplets released from an infected person’s mouth or nose when they sneeze, cough or breathe. Larger droplets can travel as much as six feet from their source — hence the six feet of social distancing we’ve all heard so much about.
But Zhai points out that it is hard to pinpoint the perfect distance of separation to ensure 0% chance of transmission. While small and fine droplets represent a much lower concentration of the infectious material, they can travel much further from their source — up to 30 feet, he says.
Studies have shown that face coverings of any sort are more effective at source containment — keeping sick individuals from transmitting those droplets — than they are at protecting healthy individuals from airborne droplets. But Zhai says the prevalence of asymptomatic carriers complicates things.
“Unfortunately, at the moment, it’s hard to tell who is who. So, in that case, we should encourage everybody to wear masks,” he said.
Which masks should we wear and how should be wear them?
Zhai says that cloth masks are not all made equal. It’s important to find a balance between filtering efficacy and breathability. His ideal construction is three layers of 100% woven cotton material, which will prevent most large particles from passing through, but won’t suffocate.
It’s also important to consider mask fit. Zhai says that for close encounters, in the range of those larger droplets that are more directional, filter efficacy is more important. But for longer distances — where you’re talking about the smaller droplets that diffuse into the ambient air — it’s important to have a good, tight fit all the way around the face. N95 masks do this very well. That’s why they are so in demand by those front line medical workers.
To that end, Zhai prefers masks with ties that go around the head over the ear loop kind. He says they are easier to adjust for a tighter fit.
But, an ideal fit is pretty much impossible to achieve with regular surgical masks, much less homemade cloth face coverings. So, for those who want to be extra cautious, Zhai pointed to a simple trick using rubber bands to jury-rig a tight fit that works with almost any type of face covering.
Some masks available through independent manufacturers online boast HEPA filters embedded in the layers of cloth. Zhai strongly warns against this type of construction for two reasons. HEPA filters are good at cleaning air on the scale of building systems, but they would restrict breathing too much when built into a mask. Of course, an even bigger issue is that HEPA filters are made from fiberglass – a dangerous substance to inhale. It’s not a material you want to use anywhere near your face.
How to handle masks after use
Cloth mask users should be deliberate about handling their masks after each use. To remove the mask, Zhai cautions against touching the outside of the mask.
“Use your finger to just remove the band or the tie. Just touch that part. When you fold it, don’t touch the external part, touch the inside part, because that’s your own particles, not from other people,” he advised. Then wash your hands immediately.
After successfully removing the face covering without contamination, launder it before reuse. A standard wash and dry cycle should be sufficient.