Efficacy and Safety of Weekly Ultraviolet Germicidal Irradiation for the Reuse of N95 Filtering Respirators

Background During the ongoing coronavirus disease (COVID-19) pandemic, N95 filtering facepiece respirators (N95 respirators) are in short supply in many countries. Considering this, the Centers for Disease Control and Prevention suggested reusing N95 respirators and recommended the use of ultraviolet germicidal irradiation (UVGI) for sterilizing the respirators. However, only a few reports have described UVGI protocols for sterilizing the N95 respirators for reuse. Therefore, in this study, we aimed to develop and evaluate a novel method for the reuse of N95 respirators after sterilization by UVGI. Methods Before conducting the study, the function of N95 respirators after multiple UVGI with a total dose of up to 10 J (1 J/cm² or more per dose) was assessed by measuring the particle collection efficiency and ventilation resistance. The participants used N95 respirators during work if they passed the fit test. After use, the respirators were sterilized using UVGI (1 J/cm²) and stored in a breathable paper bag for a week. The procedure was repeated up to three times after confirming the successful results of the fit tests. Results The particle collection efficiency without UVGI was 96.7%, while those after one, five, and 10 cycles of UGVI were 96.8%, 97.2%, and 97.2%, respectively. Ventilation resistance without UVGI was 42 Pa, and 43 Pa, 42 Pa, and 41 Pa after one, five, and 10 cycles of UVGI, respectively, which satisfied the Japanese national certification standard DS2. All 43 participants passed the fit test before the first reuse, and 39 participants (90.7%) completed the entire study protocol. The results of this study showed that N95 respirators could be used safely after repeated UVGI treatment. Conclusions This study developed a novel method for reusing the N95 respirators. A few cycles of UV radiation N95 masks retain their functionalities and can be reused with proper UVGI.