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is the (which was not peer-reviewed) The copyright holder for this preprint .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 treatments, the efficiency has a sharp drop which continues at cycle 10 (Table S2 ). Similar to the alcohol and chlorine solution treatments, the pressure drop can be maintained at ~8-9 Pa, but the efficiency has degraded to around ~80%, which would be concerning in an environment with high viral aerosol concentrations. As with the solution treatments, the pressure drops remained similar, which suggests it is also due to the decay of static charge. The dwelling time and frequency may be critical for how well the static charge can be preserved. If steam treatments saturate the fibers many times and can condense water droplets on the fibers, it is possible that the static charge decays after multiple treatments. As this decay is due to the direct water molecule contact with the fibers, it may be possible to alleviate the static decay if the fibers do not come into contact with the vapor directly (sealed container, apparatus, bag, etc.) and steam only serves as the heating element. Given that steam also resulted in eventual efficiency degradation, we further determined the limits of temperature and humidity. We performed multiple humidity experiments (30%, 70%, and 100% RH) at 85 °C (20 minutes/cycle), observing that no appreciable degradation of efficiency at any humidity level (Fig. 4a-b) . At 85 °C, 30% RH, we observed no efficiency degradation over fifty cycles on a meltblown fabric (Fig. 4c-d) . Using less harsh conditions (75 °C, dry heat), the results are expectedly in agreement ( Figure S2 ). This is further confirmed when testing multiple N95-level FFRs from various countries (listed in methods) at 85 °C, 30% and 100% RH for 20 cycles (Fig. 4e-f ). Testing conditions for the FFRs were under a flow rate of 85 L/min. From all the FFRs, we observed little change in the filtration properties, as all FFRs with filtration efficiency >95% were able to retain filtration efficiencies >95% after 20 cycles of heat treatment, even in a humid environment.