Assessment of N95 respirator for reuse after sterilization: filtration efficacy, breathing resistance, quality factor, chemical structure and surface charge density

Kumar, A.; Subramanian, V.; Joshi, S.; Venkatraman, B.

In the present ongoing pandemic, the N95 respirator is an essential protective barrier to suppress the spread of the SARS-Cov-2 virus and protect the frontline worker from exposure. The N95 respirators are meant for single usage; however, they can be used after decontamination in-light of the economy and shortfall in availability. At this juncture, the respirators performance after various types of sterilization and usage condition is required to be analyzed in detail. With this motto, this work has proceeded. The filtration efficiency, pressure drop, and quality factor of the respirator are evaluated for two face velocities (5.8 and 26.4 cm/s) following different sterilization methods. Sterilization techniques used here are dry air oven heating, gamma irradiation, and immersing in a 10% concentration of liquid hydrogen peroxide. The particle filtration performance and electrostatic surface charge density measurement are used to determine the facemasks efficacy after sterilization. The methods recommended to sterilize N95 masks without affecting their performance are (i) using dry air heat at 80oC and (ii) H2O2 soaking. The highest reduction in filtration efficiency is observed to be 30-35% after gamma irradiation due to a change in the electrostatic properties of the respirator layers. However, the filtration efficiency does not change significantly for other sterilization methods despite a change in charge density, but there is no direct correlation with filtration efficiency. Electrostatic charge measurement of the filtration layer is a crucial indicator of filtration efficiency degradation. Policymakers can use these data during potential future N95 shortage to assess the viability of sterilization methods.