More evidence, if any were needed, of the efficacy of face masks in reducing the transmission of the coronavirus.
A research team from University of Califronia, Davis and the Icahn School of Medicine at Mount Sinai, have shown that a face mask is effective at reducing the production of aerosols from talking or coughing, despite leakage around the sides.
The point that often seems to be lost on the selfish evangelical Christians who refuse to wear a face mask having been fooled into thinking they're some sort of anti-Trump political statement with which, as loyal Trumpanzee cultists, they are obliged to disagree, is that masks protect other people from you. But protecting your friends and family and the wider community is not something that seems to trouble evangelicals overmuch, as other surveys have shown.
The point is not lost however, on those socially responsible individuals who recognise that, in a pandemic such as the current one, we all have a moral obligation to help protect others as well as ourselves, to reduce the number of deaths and serious illnesses and to conserve health-care resources for those who really need them. It is reassuring to those people that they have been doing the right thing all along.
As the UC, Davis news release explains:
The team's findings are published, open access, in the Journal Scientific Reports:Wearing masks and other face coverings can reduce the flow of airborne particles that are produced during breathing, talking, coughing or sneezing, protecting others from viruses carried by those particles such as SARS-CoV2 and influenza.The researchers looked at particles flowing from these gaps by sitting volunteers in front of an instrument that counts airborne particles down to a size of half a micron. The 12 volunteers read aloud or coughed, with and without a surgical mask of the type widely used by the public, either with their mouth directly in front of the funnel of the particle counter, turned to the side or with their head lowered or raised to count particles passing directly through the mask or leaking around the sides.
While air escape does limit the overall efficiency of surgical masks at reducing expiratory particle emissions, such masks nonetheless provide substantial reduction. Our results confirm that mask wearing provides a significant reduction in the probability of disease transmission via expiratory particles, especially when both infected and susceptible individuals wear masks.
Masks also redirect the flow of air from a high-velocity plume from the talker or cougher toward anybody in front of them.
Lead author
Professor Christopher Cappa
Professor of civil and environmental engineering
University of California, Davis
The researchers found that wearing a mask while talking reduced particles directly through the mask by an average of 93%, from the bottom by 91%, the sides by 85% and the top by 47%, although with substantial variability between individuals. They got similar results for coughing.
Models to measure leakage
The team used simulations to model the overall reduction in particles due to wearing a mask, allowing for leakage around the edges. They calculated that the overall efficiency of masks was about 70% for talking and 90% for coughing.
“While air escape does limit the overall efficiency of surgical masks at reducing expiratory particle emissions, such masks nonetheless provide substantial reduction,” Cappa said. “Our results confirm that mask wearing provides a significant reduction in the probability of disease transmission via expiratory particles, especially when both infected and susceptible individuals wear masks.”
Masks also redirect the flow of air from a high-velocity plume from the talker or cougher toward anybody in front of them, Cappa said.
(a) Illustration of the experimental setup showing a participant wearing a surgical mask in the through-mask (forward) orientation. (b) Photographs of the participant position for the four different sampling orientations: forward, top, side, and bottom sampling. (c) Example microphone recording for participant M1 while speaking the rainbow passage with no mask, and (d) the associated particle counts by the APS.
AbstractAlthough the mass vaccination programmes are playing a huge part in reducing deaths and hospitalisations in places such as the UK, they are not 100% effective at preventing infections and may even increase the rate of asymptomatic infections. There is also the danger of longer-term disability from 'long-covid', especially so for the younger adults who have not yet been fully protected. It is thus imperative that we all continue to wear a face mask in public spaces, especially indoors and on public transport. And with new variants such as the recently-emerged Δ-variant evolving a higher level of infectivity, anything that reduces the viral load you might pass onto others will be worthwhile.
Wearing surgical masks or other similar face coverings can reduce the emission of expiratory particles produced via breathing, talking, coughing, or sneezing. Although it is well established that some fraction of the expiratory airflow leaks around the edges of the mask, it is unclear how these leakage airflows affect the overall efficiency with which masks block emission of expiratory aerosol particles. Here, we show experimentally that the aerosol particle concentrations in the leakage airflows around a surgical mask are reduced compared to no mask wearing, with the magnitude of reduction dependent on the direction of escape (out the top, the sides, or the bottom). Because the actual leakage flowrate in each direction is difficult to measure, we use a Monte Carlo approach to estimate flow-corrected particle emission rates for particles having diameters in the range 0.5–20 μm. in all orientations. From these, we derive a flow-weighted overall number-based particle removal efficiency for the mask. The overall mask efficiency, accounting both for air that passes through the mask and for leakage flows, is reduced compared to the through-mask filtration efficiency, from 93 to 70% for talking, but from only 94–90% for coughing. These results demonstrate that leakage flows due to imperfect sealing do decrease mask efficiencies for reducing emission of expiratory particles, but even with such leakage surgical masks provide substantial control.
Cappa, Christopher D.; Asadi, Sima; Barreda, Santiago; Wexler, Anthony S.; Bouvier, Nicole M.; Ristenpart, William D.
Expiratory aerosol particle escape from surgical masks due to imperfect sealing
Scientific Reports; 11, 12110 (2021). https://doi.org/10.1038/s41598-021-91487-7
Copyright: © 2021 The authors. Piblished bySpringer Nature Ltd.
Open access. Reprinted under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
The vaccines have undoubtedly broken the link between infection and serious illness, but they haven't yet delivered a SARS-CoV-2-free environment. That can only come about by reducing the transmission rate to very low levels. Scientists and the medical profession are doing thei bit; wearing a face mask is the least we can do.
Scientists and the medical profession are doing their bit;
wearing a face mask is the least we can do.
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wearing a face mask is the least we can do.
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