It takes quite a lot for me to read a Physics paper. Of the the three, traditional “main” branches of science, Physics was my least favourite. And that’s saying something, given that one of the others is Chemistry.
However, this paper by Verma et al. in the journal Physics of Fluids (please try to restrain your excitement, readers) is actually rather interesting and offers further evidence that masks with exhalation valves are frankly useless in the fight against Covid-19. It also adds that those plastic face shields people are starting to use are equally kak. (In addition, they are not “cloth covering the nose and mouth”, so technically not legal either. Not that that will bother anyone in SA.)
…there is an increasing trend of people substituting regular cloth or surgical masks with clear plastic face shields and with masks equipped with exhalation valves. One of the factors driving this increased adoption is improved comfort compared to regular masks. However, there is a possibility that widespread public use of these alternatives to regular masks could have an adverse effect on mitigation efforts.
Just for the record: “improved comfort compared to regular masks” just means “people being overly dramatic about having to wear a mask”. Having “an adverse effect on mitigation efforts” is merely fancy language for “won’t work at stopping the transmission of Covid-19”.
And there are some more of those lovely visualisations of coughs and sneezes, which I screenshotted.
For the clear plastic face shield:
And for the mask with exhalation valves:
Full descriptions and even some delightful (and educational) videos on that link through to the paper, but basically (as you may have already guessed), green cloud is not good. And there’s a lot of green cloud in those images.
So. If you are one of those people who wears one of these masks or face shields or you know someone who does, please (politely) let them know that they’re not helping the situation at all.