Experts claim it’s time to start using a medical-grade respirator, or wearing a surgical and cloth mask together, as new, more transmittable variants of the coronavirus spread.
For some time, scientists have agreed that the main way in which the virus spreads is through the air rather than surfaces, and there is growing evidence that small droplets of ordinary breathing and speech that can travel many meters (yards) are a common mode of transmission.
Adding to this is the increased contagiousness of emerging strains, such as B.1.1.7, which requires a smaller viral load to induce symptomatic Covid-19 compared to the more common strain.
Fit and filtration
Back when authorities first recommended individuals to wear face covers, there was an extremely short supply of proper masks and the public was encouraged to fashion provisional solutions from T-shirts or bandanas. These are far from ideal, however.
Linsey Marr, a civil and environmental engineering professor at Virginia Tech, who studies the transmission of airborne diseases, told AFP, “How well a mask works depends on two things: filtration and fit.”
“Good filtration removes as many particles as possible, and a good fit means that there are no leaks around the sides of your mask, where air — and viruses — can leak through,” she said, adding that even a small gap could lead to a 50% reduction in efficiency.
The best materials for blocking small particles include non-woven polypropylene, which is used to produce N95s and several surgical masks, and HEPA filters. Among the fabrics, tightly woven cotton fits best, she said.
“If you wear a cloth mask, choose one that has multiple layers, ideally one with a pocket that you can slip a good filter material into,” Marr said. “Or you can double mask by wearing a surgical-type mask with a tight-fitting cloth mask over it.”
Surgical masks are made of a material that filters things out well but appears to be loose, so adding a fabric mask to the top locks the edges down and prevents leakage.
Adding an extra layer increases filtration—-if one layer traps 50 per cent of all particles, the combination of two makes up 75 per cent.
But, she added, “We do not recommend wearing more than two masks. Adding more layers proves diminishing returns and can compromise breathability. It must remain easy to breathe through the layers; otherwise, the air is more likely to leak in around the sides of the mask.”
Masks with a metal nose bridge help ensure a snug fit, as do bands that tighten around the head, not just the ears. Braces that boost the fitness of surgical masks are now available on the market.
“You should feel the mask sucking inward when you breathe in, and if you hold your hands around the sides of the mask, you should not feel any air leaking out when you breathe out,” Marr said.
Another option is getting hold of N95s, or their international equivalents such as KN95, FFP2 etc.
Ranu Dhillon, a global health physician at Brigham and Women’s Hospital and Harvard Medical School, “They all have a similar degree of filtration, meaning particle safety going in and out.
Dhillon, who has been promoting better masks since last spring, is disappointed by the absence of consistent messages on the importance of better masks to the public.
What’s more, “there’s not been a concerted push to really mass produce and mass distribute these higher calibre masks.”
Health care staff have their masks professionally checked every year to make sure they make the correct seal, but Dhillon doesn’t see this as a big obstacle.
“To teach people to fit a mask, even if not 100 per cent perfectly, but more effectively, is something that’s very doable.”
Masks in the future?
Donald Milton, a professor of environmental health at the University of Maryland, said that thinking about cigarette smoke is the key to conceptualizing the hazard.
Ventilation certainly helps, but the virus can always enter you if you are between a person who breathes and an exhaust vent, which makes good masks so important, he said.
Milton and Dhillon are cautiously hopeful that under President Joe Biden’s administration, their appeals could soon become policy, and CNN reported last week that the US government was working on the first official guidelines for masks.
Milton and other aerosol scientists researching the flu concluded prior to the pandemic that it was also transmitted from tiny droplets of ordinary speech and breathing, and that the function of sneezing, coughing, and surface transmission was smaller than expected.
At the time, their results sparked debate, but Covid-19 has revived interest in the study – meaning masks during difficult flu seasons may be a regular sight, long after the pandemic has receded.