In reply to Terry Blanton's message of Sat, 4 Apr 2020 18:35:31 -0400: Hi, [snip] >I found an old Hoover HEPA vacuum bag and thought to make a mask. Then I >Googled the idea. Nothing new under the sun. HEPA spec is 300 nm but test >show them effective down to 50 nm (depends on the rating). SARS-CoV-2 is >125 nm.
I think the size of the virus is irrelevant. The mask doesn't really have to stop individual virus particles, it only has to stop the moisture droplets that carry them. Droplets are thousands of times larger than the virus. A normal handkerchief/silk scarf should do fine provided that there are no spaces around edge where droplets can bypass the filter. Regards, Robin van Spaandonk local asymmetry = temporary success
