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.
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.