[AR] Re: ... Coronavirus
- From: Peter Fairbrother <peter@xxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Mon, 23 Mar 2020 07:25:52 +0000
On 23/03/2020 00:51, Norman Yarvin wrote:
[...] N95 [...] I'm not sure if higher-rated disposable masks exist,
N100 disposable respirators do exist, the 3M 8835 and 8835+ (updated
more reuseable 8835) are examples.
but even if you did have a N100 disposable mask, enough air would leak around
the edges to render the "100" meaningless.
Good N100s (~FFP3 in EU speak) have a 20mm plus wide elastomeric face
seal, providing about as good a seal as a reuseable. The elastic also
goes round the back of the head, not just over the ears, for a firmer
and more positive fit.
P100 (oil resistant) respirators are not just for paint spraying, you
can put vaseline on the seal to further improve it.
The N-100 standard is for <99.7% filtration at 600 nm - coronoviruses
are about 110 nm across, so that standard isn't entirely applicable.
Masks vary a lot, the 2017 paper I linked to in my last post has details
of measured filtration at different sizes for different masks:
Size-Resolved Penetration of Filtering Materials from CE-Marked
Filtering Facepiece Respirators
by Norbert Serfozo, Jakub Ondráček, Naděžda Zíková, Mihalis Lazaridis,
Vladimír Ždímal
The best filtration at 110 nm mentioned in the paper is about 99.98% for
8835's.
But there is also the question of whether COVID is spread by droplet or
aerosol (like droplet but the drops are smaller, sometimes just a single
virus).
Aerosol is bad because unlike droplets which settle fairly quickly they
can stick around in the air indefinitely, and also thereby spread more
widely.
It is thought possible that aerosolised COVID can stay infective for up
to 3 hours.
If you want to home build a powered air supply helmet or hood, I'm told
a couple of good quality HEPA vacuum cleaner filters will get you good
virus filtration.
Peter Fairbrother
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