Recharging improves efficiency of decontaminated N95 masks

Hossain, Emroj; Bhadra, Satyanu; Jain, Harsh; Bhattacharya, Arnab; Ghosh, Shankar; Levine, Dov

N95 masks form a critical part of the personal protective equipment used by frontline health-care workers, and are typically meant for one-time usage. However, the recent COVID pandemic has resulted in a serious shortage of these masks leading to a worldwide effort to develop decontamination and re-use procedures. A major factor contributing to the filtration efficiency of N95 masks is the presence of an intermediate layer of charged polypropylene electret fibers that trap particles through electrostatic or electrophoretic effects. This charge degrades quickly when the mask is used. Moreover, simple decontamination procedures (e.g. use of alcohol) immediately degrade any remaining charge from the polypropylene, thus severely impacting the filtration efficiency post decontamination. In this brief report, we summarize preliminary results on the development of a simple laboratory setup allowing measurement of charge and filtration efficiency in N95 masks. We show how the charge on the mask changes due to decontamination treatments, and correlate with reduced filtration efficiency. Additionally, we propose and show that it is possible to recharge the masks post-decontamination treatment and recover filtration efficiency. Importantly, recharging can be performed using readily available equipment and materials, and so can be employed both in urban and rural settings. We emphasize that because of the current worldwide lockdown, the measurements reported in this report are preliminary, performed with hastily constructed home-built equipment on a small variety of masks available to us. Although we are confident in our results, we encourage groups with special-purpose equipment to redo and verify our experiments.