See update below.
-sigh-
Study: Masks Help Against COVID, Some Better Than Others
A new study examining masks effectiveness in protecting against COVID-19 infection finds N95-style masks to be more effective than surgical masks or other cloth coverings, adding scientific backing to the argument masks do provide some level of protection.
Izzat so? Let’s look at the study.
The present study experimentally investigates the dispersion and build-up of an exhaled aerosol modeled with polydisperse microscopic particles (approximately 1 μm mean diameter) by a seated manikin in a relatively large indoor environment.
[…]
Nevertheless, high-efficiency masks, such as the KN95, still offer substantially higher apparent filtration efficiencies (60% and 46% for R95 and KN95 masks, respectively) than the more commonly used cloth (10%) and surgical masks (12%), and therefore are still the recommended choice in mitigating airborne disease transmission indoors.
Hmm. So the masks types are effective at filtering 1 micron test particles at these levels:
R95: 60%
KN95: 46%
Cloth (3-ply): 10%
Surgical: 12%
So the procedure/dust masks virtually everyone is wearing are very nearly ineffective. For 1 micron particles.
However SARS-CoV-2 averages 0.125 microns. That would be 0.125 into 1…
The SARS-CoV-2 virus is eight (8, ocho) times smaller than the 1 micron test particle. If your mask is only 12% effective against 1 micron, it’s probably around 1.5% effective against ChinCOVID.*
And frankly, the test was all wrong anyway. None of these masks are designed to protect other people from viral spread, at most they protect the wearer. That is what they were designed to do.
* Yes; since I’m an asshole, I did email the study author and point this out.
Update: And I got a reply from Professor Yarusevych. A rather eyebrow-raising one.
Thank you for your interest. There is no issue with the methodology. The selected particle size represents particles that follow air flow. They are 10 larger than a single virus, which means their volume is about 1000 times larger. Thus, such small particles can carry a significant number of viral copies. I hope this alleviates your concern.
Apparently he assumes that SARS-CoV-2 will only be aerosolized in relatively large aerosols; that there couldn’t possibly be more smaller aerosols, but carrying fewer viruses each.
Added: Let’s be fair. Is his 1 μm assumption valid? The Mechanism of Breath Aerosol Formation suggests an exhalation aerosol range of .5 μm to .9 μm. (Added: It’s worth mentioning that .5 μm was just the detection threshold of the detection equipment, and that smaller aerosols were likely present.)
| If you found this post useful, please consider dropping something in my tip jar. I could really use the money, what with ISP bills, SSL certificate, and general life expenses.Click here to donate via PayPal. |
NEVER admitt a lie once started.No matter what.
This is what they are doin.
I’ve glanced at some of the professor’s other papers. I think he’s honest. I just think he made one bum assumption about aerosol size. Or maybe he found a different paper that yielded 1 μm aerosols. It isn’t as if I’m an expert in the field.
Well… and I probably would have used an aerosol more volatile than olive oil, but his way does give greater worst-case scenario dispersal; so there is something to be said for that.
Sounds like he assumed a size that would make masks effective, but not cloth.
Except his test didn’t show the N95s to be particularly effective at preventing dispersal either. Which they wouldn’t be, since that’s not what they’re designed for.