J
Joe Gwinn
Guest
On the matter of masks and COVID19, there has been a lot of obsession
with getting 95% percent rated masks (even if nobody wears them well
enough to achieve that level of performance). Anyway, there is a
back-of-the-envelope analysis that bounds the problem:
Assume that we have a population where the same kind of mask is worn
by all, and that this mask is only 75% effective (this is low).
People spend most of their time talking, not coughing, so we will use
talking for this example. The math is the same.
Person A is talking, generating droplets. A\'s mask stops 75% of the
droplets and passes the remaining 25%.
Person B is listening. B\'s mask blocks 75% of A\'s 25%, and passes 25%
of that 25% along, receiving a net of 6.25%.
The current value of R (number of people who catch COVID per infected
person) is say 5 (this is high). The net value of R is thus
(5)(0.25)(0.25)= 0.3125, well below the unity required for COVID to
even hang on, never mind grow.
Joe Gwinn
with getting 95% percent rated masks (even if nobody wears them well
enough to achieve that level of performance). Anyway, there is a
back-of-the-envelope analysis that bounds the problem:
Assume that we have a population where the same kind of mask is worn
by all, and that this mask is only 75% effective (this is low).
People spend most of their time talking, not coughing, so we will use
talking for this example. The math is the same.
Person A is talking, generating droplets. A\'s mask stops 75% of the
droplets and passes the remaining 25%.
Person B is listening. B\'s mask blocks 75% of A\'s 25%, and passes 25%
of that 25% along, receiving a net of 6.25%.
The current value of R (number of people who catch COVID per infected
person) is say 5 (this is high). The net value of R is thus
(5)(0.25)(0.25)= 0.3125, well below the unity required for COVID to
even hang on, never mind grow.
Joe Gwinn