The N95 mask does a poor job of keeping virus particles from being inhaled from an aerosol; the water droplets are largely caught by the filter media, and then evaporate, leaving the virus to be sucked through.
The virus isn’t expected to spread by straight airborne transmission between people, but that’s poor evidence that it won’t be airborne from the distance from your mask to your lungs.
As EGI says that doesn’t seem to be correct but he is talking about N99 not N95 so I’m wondering about this.
My understanding is that the N95 standard is about filtering 95% of the particles and the test level is for particle distributions with a mean of 75nm and standard deviation of less than 2nm. SARS-C0V-2 is thought to be 80 − 120 nm in size (and generally spherical). While the smallest would be close to the mean for N95 seems to suggest 95% should still be filtered (assuming the filter is not damaged).
Adsorption air filters are not sieves or membrane filters, particles are captured by adsorption to the filter medium, not by size exclusion. The pessimum of filtration efficiency is afaik around 1 µm with higher capture efficieny below that due to higher collision probability due to more brownian motion. Not completely sure of the numbers though.
I’d go with P 99 or 100 since they are not that much more expensive / unpleasant to wear and we want to have as little particle leakage as possible since we do not know how much dose reduction is needed to reduce infection probability by one to two orders of magnitude. A hundredfold seems plenty though.
Also note that virus particles do not fly alone since they are allway bound in liquid or whatever remains after the droplet dries. CoV-2 seems to be nonviable when dried though so you need not worry about dry stuff.
Interesting. While I knew some of the filtering was stuff just sticking together I had thought some level of particle size filtering was also present—and not on a gross size scale.
See my reply to you above. That said, even if the virus was dry airborne as you assume, P3/N99 filters would still capture way above 99% of these particles as explained in my original post.
I don’t think that it’s safe to generalize “99% of particles” to “99% of virus particles”. It’s likely better than nothing and might even be adequate, especially since N95 seems to be the gold standard.
Yeah, it will be way more than 99% of virus particles since most virus particles are bound in larger droplets where filtration efficiency is much higher than 99 %.
The N95 mask does a poor job of keeping virus particles from being inhaled from an aerosol; the water droplets are largely caught by the filter media, and then evaporate, leaving the virus to be sucked through.
The virus isn’t expected to spread by straight airborne transmission between people, but that’s poor evidence that it won’t be airborne from the distance from your mask to your lungs.
As EGI says that doesn’t seem to be correct but he is talking about N99 not N95 so I’m wondering about this.
My understanding is that the N95 standard is about filtering 95% of the particles and the test level is for particle distributions with a mean of 75nm and standard deviation of less than 2nm. SARS-C0V-2 is thought to be 80 − 120 nm in size (and generally spherical). While the smallest would be close to the mean for N95 seems to suggest 95% should still be filtered (assuming the filter is not damaged).
Adsorption air filters are not sieves or membrane filters, particles are captured by adsorption to the filter medium, not by size exclusion. The pessimum of filtration efficiency is afaik around 1 µm with higher capture efficieny below that due to higher collision probability due to more brownian motion. Not completely sure of the numbers though.
I’d go with P 99 or 100 since they are not that much more expensive / unpleasant to wear and we want to have as little particle leakage as possible since we do not know how much dose reduction is needed to reduce infection probability by one to two orders of magnitude. A hundredfold seems plenty though.
Also note that virus particles do not fly alone since they are allway bound in liquid or whatever remains after the droplet dries. CoV-2 seems to be nonviable when dried though so you need not worry about dry stuff.
Interesting. While I knew some of the filtering was stuff just sticking together I had thought some level of particle size filtering was also present—and not on a gross size scale.
See my reply to you above. That said, even if the virus was dry airborne as you assume, P3/N99 filters would still capture way above 99% of these particles as explained in my original post.
I don’t think that it’s safe to generalize “99% of particles” to “99% of virus particles”. It’s likely better than nothing and might even be adequate, especially since N95 seems to be the gold standard.
Yeah, it will be way more than 99% of virus particles since most virus particles are bound in larger droplets where filtration efficiency is much higher than 99 %.
And, as I’ve said above, I think that it’s not sufficiently safe to assume that they inactivate within seconds of drying out.