A method to determine the available UV-C dose for the decontamination of filtering facepiece respirators

Aims: To develop a method to assess model-specific parameters for ultraviolet-C (UV-C, 254 nm) decontamination of filtering facepiece respirators (FFRs). Methods and Results: UV-C transmittance was quantified for the distinct composite layers of six N95 FFR models and used to calculate model-specific alpha-values, the percentage of the surface UV-C irradiance available for the internal filtering medium (IFM). Circular coupons, excised from the FFRs, were exposed to aerosolized particles containing MS2 coliphage and treated with IFM-specific UV-C doses ranging from 38 to 4707 J m-2. Models exposed to a minimum IFM dose of 1000 J m-2 demonstrated at least a 3 log reduction (LR) in viable MS2. Model-specific exposure times to achieve this IFM dose ranged from 2 to 266 min. Conclusions: UV-C transmits into and through FFR materials. LR of MS2 was a function of model-specific IFM UV-C doses. Significance and Impact of the Study: Filtering facepiece respirators are in high demand during infectious disease outbreaks, potentially leading to supply shortages. Reuse of disposable FFRs after decontamination has been discussed as a possible remediation strategy, but to date lacks supporting scientific evidence. The methods described here can be used to assess the likelihood that UV-C decontamination will be successful for specific FFR models.