This study proves masking works, right?

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Yves Smith over at Naked Capitalism uses this masking study as compelling evidence that masking works. I read the study and have a few observations.

The study…

The study looked at a variety of masks: N95, medical, and cloth. It used a mask on a dummy’s head to test the mask’s fit, then affixed the mask in an airtight fashion to an inhalation-simulating collector and placed the collector with mask affixed in an airtight chamber. The chamber was emptied. Particles between 0.3 and 2 microns were pumped into the chamber and the collector tracked the particle count with the mask. The collector was tested in similar fashion without masks as a baseline.

Study design problems…

0.3 to 2 microns is waaaay too big of a particle size to study. SARS-COV-2 is about 0.1 micron in size. It will go through masks like mosquitos through a pasture fence. B-b-but particles are droplets! Not necessarily. In a dry environment, water will evaporate from droplets around a size of 0.3 microns within microseconds. Droplets 1 micron in size might take a full second. 2 microns might take 5 seconds. Best case for masks stopping droplets is if the environment is humid. With humid environments, there’s a bonus. This gives you a head start on your microbiology experiment where you get to culture lots of pathogenic bacteria in your wet mask!

In vitro problems…

It is very difficult to model living systems accurately. The study measured only simulated inhalation, but mammals exhale as well. Exhaling will affect mask fit and allow some exchange between air inside and outside the mask. Exhaling will also allow droplets from your breath to be absorbed by the mask. And those droplets will contain viruses of various kinds. And your mask’s water content will increase and viruses from outside your mask will diffuse in the wet mask environment onto the inner side of the mask and potentially be inhaled. And the viruses from your breath initially trapped on the inner side of the mask will diffuse to the outside and potentially be exhaled. If you are wearing your mask in a humid environment and go into a dry environment, you will certainly get viral exchange via your mask as the mask dries.

None of these problems are addressed by the study. Sorry, Yves, the study you relied on is not compelling in the least.