Global shortages of N95 masks have led to an urgent need of N95 decontamination and reuse methods that are scientifically validated and available globally. Although several large scale decontamination methods have been proposed (hydrogen peroxide vapor, UV-C); many of them are not applicable in remote and low resource settings. Heat with humidity has been demonstrated as a promising decontamination approach, but care must be taken when implementing this method at a grassroots level. Here we present a simple method to provide stable humidity and temperature for individual N95 masks which can be simply scaled in low resource settings. Moist heat (>50% humidity, 65-80C temperature) was applied to Kimberly-Clark N95 respirators for over 30 minutes by placing sealed containers with N95 respirators into water that had been brought to a rolling boil and removed from heat, and then allowing the containers to sit for over 45 minutes. After rising to their threshold points, temperature and humidity remained above 65C and 50% for a treatment time of at least 30 minutes. Filtration efficiency of 0.3-4.99um particles remained above 97% after 5 treatment cycles across all particle size sub-ranges, which is consistent with previously-reported data for similar heat and humidity conditions on different N95 FFR models. Although no fit tests were conducted on these masks after treatment, prior data on moist heat based treatment indicates consistent fit for up to five cycles of decontamination. This method of applying heat and humidity for the purpose of N95 respirator decontamination can be implemented on open flame stoves for low resource settings without reliable electricity access or where other methods of decontamination are not accessible. Higher temperatures or longer treatment times, such as treatment at >70C for over 30 minutes, could be achieved by increasing the volumes of boiled water used. Although fresh N95 masks should always be used - whenever available - we believe this simple yet reliable method provides a low cost, electricity free method for N95 decontamination in remote parts of the world.

Global shortages of N95 respirators have led to an urgent need of N95 decontamination and reuse methods that are scientifically validated and available world-wide. Although several large scale decontamination methods have been proposed (hydrogen peroxide vapor, UV-C); many of them are not applicable in remote and low-resource settings. Heat with humidity has been demonstrated as a promising decontamination approach, but care must be taken when implementing this method at a grassroots level. Here we present a simple, scalable method to provide controlled humidity and temperature for individual N95 respirators which is easily applicable in low-resource settings. N95 respirators were subjected to moist heat (>50% relative humidity, 65–80°C temperature) for over 30 minutes by placing them in a sealed container immersed in water that had been brought to a rolling boil and removed from heat, and then allowing the containers to sit for over 45 minutes. Filtration efficiency of 0.3–4.99 μm incense particles remained above 97% after 5 treatment cycles across all particle size sub-ranges. This method was then repeated at a higher ambient temperature and humidity in Mumbai, using standard utensils commonly found in South Asia. Similar temperature and humidity profiles were achieved with no degradation in filtration efficiencies after 6 cycles. Higher temperatures (>70°C) and longer treatment times (>40 minutes) were obtained by insulating the outer vessel. We also showed that the same method can be applied for the decontamination of surgical masks. This simple yet reliable method can be performed even without electricity access using any heat source to boil water, from open-flame stoves to solar heating, and provides a low-cost route for N95 decontamination globally applicable in resource-constrained settings.

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