The possible loss of functionality of the face masks after physical disinfection is a crucial consideration in order to evaluate the viability of such practice. Radiation and heat could definitely affect the materials of the mask, rendering it unsafe for further usage. We considered this when establishing the energies and time of exposure to safely operate the device.
Regarding UVGI effects on face masks, we found studies showing that it can be safely used without altering aerosol penetration and filter airflow resistances. One study reported no significant alteration of these filtration properties after using UVGI with dosages as high as ~1000 J/cm2 (1), which are several orders higher than our proposed dosage. Another study reported that no detrimental effect was observed when using dosages of 176-181 mJ/cm2 (2). Further studies of the same research group found that this results could be extended at least to a 3X cycle using a total dosage of 1,62 J/cm2 (3)—which is within the same order of our intended dosage—. According to this evidence, we consider that our intended dosage will probably not affect the filtration capacity of the masks for at least three cycles of disinfection.
In terms of the effect of heat, the reports are much more scarce. There are no assays are using dry heat, as we intend. The last study that we referenced for the UVGI used moist heat at 60°C and 80% RH for 30 min and observed no significant decrease in filtration capacities of the masks (3). This is the closest report we could find to our intended disinfection method, and so we chose the same temperature range, which we consider to be enough to remove almost all viral infectivity and also takes into account the functionality of the mask after the disinfection.
- Lindsley WG, Martin SB, Thewlis RE, Sarkisian K, Nwoko JO, Mead KR, et al. Effects of Ultraviolet Germicidal Irradiation (UVGI) on N95 Respirator Filtration Performance and Structural Integrity. J Occup Environ Hyg [Internet]. 2015 Aug 3 [cited 2020 Apr 2];12(8):509–17. Available from: http://www.tandfonline.com/doi/full/10.1080/15459624.2015.1018518
- Viscusi DJ, Bergman MS, Eimer BC, Shaffer RE. Evaluation of Five Decontamination Methods for Filtering Facepiece Respirators. Ann Occup Hyg [Internet]. 2009 [cited 2020 Apr 2];53(8):815–27. Available from: https://academic.oup.com/annweh/article-abstract/53/8/815/154763
- Bergman MS, Viscusi DJ, Heimbuch BK, Wander JD, Sambol AR, Shaffer RE. Evaluation of Multiple (3-Cycle) Decontamination Processing for Filtering Facepiece Respirators. J Eng Fiber Fabr [Internet]. 2010 Dec 15 [cited 2020 Apr 2];5(4):155892501000500. Available from: http://journals.sagepub.com/doi/10.1177/155892501000500405