Impact of the Contamination Method on the Disinfection of N95 Respirators: Drops versus Aerosols

The recent surge in the use of filtering facepiece respirators (FFRs) during the SARS-CoV-2 pandemic triggered economic and environmental concerns with regards to their safe reuse and/or disposal. Their decontamination through ultraviolet (UV) irradiation has proven efficient in bench tests. Nevertheless, no study has yet investigated to what extent the decontamination method’s performance was impacted by the contamination method. In this study, Bacillus subtilis spores were inoculated in three suspensions used to contaminate coupons of FFRs via aerosols nebulisation or 2 µ L drops deposition. The contaminated coupons were then exposed to UV irradiation in a monochromatic UVC lamp collimated beam reactor. The results revealed that contamination and decontamination were more efficient for drops (maximum 0.72 log losses and 3 log inactivation at 150 mJ cm –2 ) than for aerosols (maximum 2.47 log losses and 1.75 log inactivation at 150 mJ cm –2 ). Inactivation was greater in coupons contaminated using artificial saliva, followed by phosphate buffer solution, and finally artificial saliva with mucin which also presented the highest fraction of resistant spores, based on kinetic modeling. Disinfection was determined sensitive to the method of contamination ( p < 0.001). However, the composition of the contaminating suspension was the most important performance predictor for decontamination by UV irradiation ( p = 9.2 × 10 –10 ).