August 23, 2021

New study highlights need for better face masks, good ventilation

By: Judy Mathias

Editor's Note

A new experimental study by engineering researchers in the Fluid Mechanics Research Laboratory at the University of Waterloo, Ontario, Canada, finds that most cloth and disposable masks (3-ply cotton and 3-ply blue pseudo-surgical masks) filter only 10% of exhaled aerosol droplets because of fit. The remaining aerosols are redirected, mostly out the top of the mask where it fits over the nose, and escape into the ambient air unfiltered.

Higher quality N95 and KN95 masks, which have filtration efficiency of 95% with ideal fit, only had filtration efficiencies at 46% and 60%, respectively, because of leakages through gaps in the fit of the masks. Tests conducted 2-meters (about 6.5 feet) distance from the subject captured significant aerosol build-up in the indoor space over a 10- hour period.

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Ventilation tests showed that even modest ventilation rates led to lower aerosol build-up compared to the best performing mask in an unventilated space.

The researchers say the much greater effectiveness of N95 and KN95 masks if worn correctly makes a compelling case that they should be worn in indoor settings, such as schools and workplaces, as much as possible.


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