UV disinfection of N95 masks: good study of repeated UV. First, past studies show “UVGI on respirator appearance, fit, airflow resistance, and filtration efficiency after 1-3 decontamination cycles and have found no sig effects”. But >3? 🧵 #COVID19 ncbi.nlm.nih.gov/pmc/articles/P…
2) In the lab, UVGI has been successfully used to decontaminate N95 respirators exposed to the bacteriophage MS2 (15,16) and influenza virus.(6,8) #COVID19
3) “However, the effects of extended exposures to UVGI after multiple decontamination cycles are not known, and it is unclear how large a cumulative dose of UVGI respirators can withstand, what damage eventually occurs, or how many times disposable FFRs could be decontaminated”
4) Four models of N95 FFRs tested. The models used were the 3M 1860 N95, 3M 9210 N95, GE 1730 N95, and Kimberly-Clark 46727 N95 respirator/surgical mask.
5) Main results - “We found that UVGI exposure led to a small increase in particle penetration (up to 1.25%) and had little effect on the flow resistance.” #COVID19 
6) Also notice Mask “B” had the lowest particle penetration of all N95 masks... which brand+model is this superior mask with much smaller particle penetration? Mask “B” is 3M 9210 model. Notice “A” is the 3M 1860 model is 2nd best. The GE “C” and KC “D” 3rd and 4th best. #COVID19
7) “the strength of the respirator materials was dramatically affected by UVGI exposure in most cases. At the highest doses, many of the layers had lost most or all of their strength, and in several cases the material was visibly degraded with obvious breaks or tears” #COVID19
8) “This suggests that the upper limit for UVGI exposure during repeated disinfection cycles would be set by the physical degradation of the respirator material and not by a loss in filtration capacity” #COVID19
9) Bottomline ➡️: it seems UV disinfection not a problem for the particle penetration integrity (KEY FOR SAFETY!), but some other physical parts degraded (which might make mask loose or break). But at least latter is visible to the user. #COVID19
10) Naturally 3M says don’t do it. But based on the 2015 study above, its seems okay for particle penetration and for flow. 3M statement: multimedia.3m.com/mws/media/1816… #COVID19
11) “IOM projected that 6-week flu pandemic would need 90 mil FFRs. OSHA predicted that a 24 week flu pandemic need 360 mil in US. A surge in demand would greatly exceed current stockpiles and production capabilities, and would almost certainly result in a shortage.”🤦🏻♂️ #COVID19
12) “Heat and steam can melt or degrade the respirator and require drying the FFR after treatment. Chemical disinfectants require rinsing and drying, and can leave an unpleasant odor or a residue that irritates the skin.” #COVID19
13) “Gaseous systems using ethylene oxide or vaporized hydrogen peroxide require ventilation controls. N95 respirators cannot be disinfected with alcohols cuz remove the electrostatic charge from the filtration media and substantially degrade filtration capacity.” #COVID19
