Testing health hazards from implementation of far-UVC irradiation as an intervention technology to reduce airborne disease transmission

As part of the NIOSH Research to Practice (r2p) approach, this research responds to the needs identified by the occupational health community for new intervention technology against disease transmission. Pathogens transmitted by airborne routes can result in disease outbreaks with major healthcare and economic consequences. The COVID-19 pandemic demonstrates the potential significance of such disease outbreaks, and NIOSH has identified reduction of transmission of infectious diseases such as influenza among workers as a Strategic Plan Research Goal (Intermediate Goal 3.3). Ultraviolet (UV) radiation (conventionally at 254 nm) is a well-established highly-efficient anti-microbial modality effective at killing bacteria and viruses. However, it is not possible to directly use conventional germicidal UV when people are present because of its well-documented human health hazards for eyes and skin. By contrast, our in vitro and in vivo preliminary studies utilizing far-UVC radiation (defined as 200-230 nm) have demonstrated similar anti-microbial properties compared to conventional germicidal UV lamps, but without corresponding safety concerns. Far-UVC radiation is generated by excimer lamps emitting primarily at a single wavelength, such as 222 nm emissions from KrCl lamps. We have previously demonstrated the utility of 222- nm lamps to inactivate >95% of aerosolized H1N1 influenza virus at a very low dose of 2 mJ/cm2, and have recently demonstrated >99.9% inactivation of aerosolized human coronaviruses with that same very low dose. Continuous overhead far-UVC radiation at very low dose rates in occupied indoor workplaces is therefore a very promising tool to limit the spread of viral and bacterial disease, including COVID-19. While the safety aspects of far-UVC radiation are based on basic biophysics – far-UVC radiation cannot penetrate the skin stratum corneum nor the optical tear layer - a major gap in our knowledge relates to the current safety regulatory limits for far-UVC radiation. While various agencies have published recommendations for exposure limits at far-UVC wavelengths, the data on which they are based are minimal, and lack the specificity to accurately reflect safety as a function of wavelength. With the proposed research we seek to supplement and improve the accuracy of these recommendations by systematically evaluating, as a function of wavelength, short and long term effects of acute and chronic far-UVC irradiation of both the eyes and the skin in mouse models. In this UV wavelength range, mouse models are appropriate for extrapolation to humans as the skin stratum corneum and the ocular tear layer are comparable in thickness, mouse to man. The far-UVC safe exposure threshold curves which will result from this work are a necessary step to improve current recommended human exposure limits in the far-UVC wavelength range, so these safety studies are a crucial factor in the