[AR] Re: ... Coronavirus
- From: Peter Fairbrother <peter@xxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Mon, 23 Mar 2020 07:23:17 +0000
On 22/03/2020 20:32, William Claybaugh wrote:
Norman, Rand:
Please correct me if I’ve got this wrong but it has previously been my
understanding that only a Level 3 or better facility has in place
filters capable of capturing virus particles. This based on a visit to
a Level 4 facility.
Level 4 threats are threats to more than just a worker, eg a disease
which could kill many if released into the wild.
Level 3 threats are less severe, but still more than just a threat to a
worker. Like level 4, they require levels of filtration and reliability
more than just those suitable to the protection of a worker.
I have previously understood that no face mask can filter virus
particles
That is incorrect, even a tea towel can filter aerosolised viruses, just
not very well. However the required level of filtration and security for
eg someone out-and-about in a COVID environment is more than a tea
towel, generally N95 respirators are recommended.
There is a small problem here though. The N specifications, and the
similar EU FFP specs, are for filtration at 600 nm, while viruses are
smaller than that. So while many (most) rated masks will effectively
filter viruses to the standard's level, some N and FFP marked masks may
not - the standards are designed for a different task.
That said, I believe that EU FFP3 gear, which (in normal circumstances)
you can easily buy, can be used in level 3 labs.
I don't know of any actual restrictions on buying level 4 ppe gear,
though there might be some dual-use export controls. But level 4 isn't
ppe at the level of disposable masks or even hoods with portable powered
air filtration (some woodworkers use these), it is full body ppe with
room-supplied air, and I have never bought my own.
and that conventional face masks create, after a few minutes use,
exactly the warm and wet environment in which bacteria and viruses thrive.
They do get warm and wet inside (though coronaviruses don't like that),
but the idea is that there are no pathogenic bacteria or viruses inside
to multiply. The problem is more from ordinary bacteria from the user's
mouth etc., especially when respirators are reused.
The utility of such masks for medical personal is—as I
understand it—only to avoid sputum in the air from coughing.
Masks, as in surgical masks, are mainly meant to protect the patient
from droplet transmission of the Doctor's bacteria etc. Droplets are
produced pretty much all the time, you will have seen people who spit as
they talk, but everybody produces droplets to some extent, even when
they are not coughing.
Respirators are different. A face shield to protect the eyes from
droplets and a N99 or FFP3 respirator - heck, even a N95 respirator - to
protect the mouth and nose against droplets and aerosolised virus will
provide pretty good, though not 100%, protection against inoculation.
The Chinese KN-95 masks you see people wearing on TV are quite clever -
the valve (a valved mask is MUCH easier to breathe through) has a thin
filter on the inside to protect others from droplets passed out through
the valve, as well as its normal function protecting the wearer from
incoming droplets and to a lesser extent aerosols.
Peter Fairbrother
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