Can N95 respirators be reused after disinfection? And for how many times?

Lei Liao; Wang Xiao; Mervin Zhao; Xuanze Yu; Haotian Wang; Qiqi Wang; Steven Chu; Yi Cui

is the (which was not peer-reviewed) The copyright holder for this preprint . https://doi.org/10.1101/2020.04.01.20050443 doi: medRxiv preprint While UV radiation may possess enough energy to break the chemical bonds and degrade polypropylene, the dosage of the sterilization chamber is relatively low, and the material degrades very slowly. This is supported by previous experiments that showed UV-C doses up to 950 J/cm 2 did not appreciably change the filtration efficiency. 34 A possible concern regarding UVGI disinfection for FFRs is of the UV penetration depth. As UV-C has a wavelength around 250 nm, and polypropylene is a UV absorber, it is difficult to conclude if smaller viral particles deep within the filter can be deactivated through UVGI. If the particles are of a larger size and remain localized on the surface, UVGI may be a candidate for FFR reuse. Furthermore, this means that UVGI requires FFRs to not be stacked, as the incident radiation is will only be absorbed by the top-most surface. Another disadvantage is that UVGI was reported to significantly impact the mechanical strength of some FFRs with doses of around 1000 J/cm 2 . 34 Therefore, UVGI may be a useful disinfection technique, but the exact exposure or intensity of the UV-C light fluence on the mask surface would need to be verified. The variation in UVGI intensity has been the cause of discrepancies in the literature, as 3M's own internal reports recently showed that their UVGI treatments damaged particular FFRs, 35 whereas other reports show that UVGI cycling on multiple N95 FFRs had minimal or no impact. 31 While most of our tests were performed on meltblown fabrics with initial efficiency >95% due to the current shortage of FFRs, there is a definite concern over whether other FFR components (straps, valves, nosepiece, foam, etc.) can change in these treatment environments. These can impact the fit and sealing of the FFR, which is equally important as the FFR efficiency itself. From our experiments, we also used typical N95-grade FFRs to test the strap elasticity and structural integrity after heat treatments. We noted no apparent or qualitative change in the strap elasticity or fit compared with the untreated model for the heat treatments, but future quantitative studies need confirm this.