Do you recall that I said this?
Next up, the wearing of masks. I have some experience in air filtration engineering from my early career testing and balancing HEPA filters and charcoal adsorbers. HEPA filters (of concern here) work by particle interception due to electrostatic force. Surgical masks, cloths, handkerchiefs, and other manner of cotton material (cotton is cellulose) do not have that.
My daughter wears one in surgery and the ER to prevent potential blood-borne pathogens from entering her mouth, not to prevent SARS-CoV-2, flu or the common cold (which is also a Coronavirus). N95 masks are just that, 95% efficient for particles down to a given size. Moreover, when a nuclear or chemical worker wears a full face respirator, if the wearer is a male and has a beard, he must shave. Workers have tried to create work-arounds for this by glazing their face with Vaseline, but the seal never works. The bulk of breathing air goes around the filtration media if there is no testable seal, not through it. This is true of full face respirators, and it is true in the superlative for these silly little masks half of America is wearing.
When you put an N95 mask on, the bulk of your breathing air is going under and over the top of the mask, not through it. Furthermore, every decontamination technique eventually destroys the electrostatic charge on the fibers, thus rendering the mask useless. It’s designed to be worn and then thrown away. It’s actually worse than useless, because we are now learning that there is a heavy viral and pathogenic loading on both the outside and the inside of the filter media, and we also now know that the degree to which a patient suffers from this disease is a function – at least partially – of the amount of inoculate that you breath.
Then I got a little more detailed and discussed particle sizes.
HEPA filters will remove particles down to 0.3 µm in size (to usually 99.95% efficiency, depending upon the filter – here I have used data for nuclear grade filters). The SARS-CoV-2 virus is 80 nm in diameter. A few viruses out of a million might be intercepted by electrostatic force, but that’s essentially zero.
If the particle you’re trying to intercept is spittle, stay away from coughing people anyway. But those particles drop by sedimentation, diffusiophoresis, etc.
0.3 µm versus 80 nm. A nanometer is 1E-9 meters, and 1 µm is 1E-6 meters. This means that a SARS-CoV-2 virus is 80E-9 / 0.3E-6 = 0.27 the minimum size necessary for even the most expensive nuclear grade HEPA filters to remove it from an air stream.
I need to caveat these statements and observe that because of the serpentine flow of air through a HEPA filter, it’s possible that there is some removal efficiency due to electrostatic force (i.e., that it’s not zero), assuming a charge on the shell of the virus. But it’s still low. While I’m not perfect, I won’t mislead readers. And while there is some small probability that there will be some small effect, any very small particulate eventually re-evolves into the air stream.
One of my major gripes with how America has turned to the medical bureaucracy during this pandemic is treating medical doctors like experts in every field of science. They’re not. A doctor isn’t an air flow and filtration engineer. A doctor isn’t an industrial hygienist. A doctor isn’t a physicist.
But it’s still nice to see that eventually they conform to the truth of what science tells us. This is straight from the New England Journal of Medicine (nejmp2006372).
We know that wearing a mask outside health care facilities offers little, if any, protection from infection. Public health authorities define a significant exposure to Covid-19 as face-to-face contact within 6 feet with a patient with symptomatic Covid-19 that is sustained for at least a few minutes (and some say more than 10 minutes or even 30 minutes). The chance of catching Covid-19 from a passing interaction in a public space is therefore minimal. In many cases, the desire for widespread masking is a reflexive reaction to anxiety over the pandemic.
You can read the rest for yourself. They eventually dive into a discussion concerning the use of masks by medical workers, and I think over-state their case (I still believe, along with my daughter, an NP, that she wears a mask for purposes of protecting herself from blood-borne diseases and spittle in the OR and ER).
However, nits here and there shouldn’t obfuscate the fact that at least they are being honest about this. Anxiety is the root of the problem, and reflexive fealty to the priesthood of the medical profession is a symptom of real problems in America concerning the lack of STEM education and knowledge.