PD05: Skin safety and efficacy of filtered far ultraviolet C for SARS-CoV-2 inactivation

E. Eadie,¹ R.P. Hickerson,^2,3 M.J. Conneely,^2,3 R. Hammond,⁴ S.K.H. Tsutsumi,² C.P. Cabrera,⁵ A. Wood,⁶ A.W. Longbottom,⁶ A.J. Parker,⁶ S.H. Ibbotson⁷ and K. Wood⁵

¹Photobiology Unit, NHS Tayside, Dundee, UK; ²School of Life Sciences and ⁷Photobiology Unit, University of Dundee, Dundee, UK; ³Ten Bio Ltd, Dundee, UK; ⁴School of Medicine and ⁵SUPA, School of Physics & Astronomy, University of St Andrews, St Andrews, UK; and ⁶Fluid Gravity Engineering Ltd, St Andrews, UK

Excimer lamps have a peak emission wavelength of 222 nm [far ultraviolet (UV)C] and have been shown in laboratory settings to inactivate SARS-CoV-2, the virus responsible for the COVID-19 pandemic. As a result, lamps are being installed worldwide to disinfect air in occupied rooms. It is claimed that this will reduce COVID-19 transmission and that the lamps are ‘safe for humans’. These claims are based predominantly on laboratory, animal and limited human studies. It was our aim to gather more evidence on both the real-world efficacy and skin safety of this short wavelength UVC radiation. We used a two-pronged research approach: (i) generation of skin safety data investigating DNA damage, immunosuppression and modifications to the skin microbiome – the innovative TenSkin™ model was used to rapidly generate these data; and (ii) computational fluid dynamics combined with Monte Carlo radiative transfer computer modelling to simulate air flow, particle generation and far-UVC irradiation of a typical classroom. A classroom (12 m × 6 m × 3 m) with four air inlets, each 20 cm × 20 cm, producing an inflow air speed of 2·5 m s^–1 was simulated. This is equivalent to six air changes per hour (ACH; typical classroom 5–7 ACH). With uniform release of particles, at a height of 0·5 m, the mechanical ventilation reduces the particle load to 6% in 30 min. The addition of 18 commercially available far-UVC lamps located in the ceiling, irradiating the room below, resulted in reduction to 3% at 30 min. Far-UVC lamps with a larger angular distribution would reduce the particle load to 0·1% at 30 min. These simulations have a restriction on exposure at 2 m that is equivalent to the legal limits of the Artificial Optical Radiation Regulations 2010. For context, irradiation of the TenSkin model with a filtered far-UVC lamp demonstrated minimal cyclobutane pyrimidine dimer formation at a dose 260 times higher than current legal limits, and this was restricted to the most superficial nonproliferating epidermal cells. The classroom simulations were repeated with the irradiation restriction set at 20 and 100 times the exposure limits, which resulted in a 99·99% reduction of particle load within 4·5 min and 1 min, respectively. Filtered far-UVC lamps cause minimal DNA damage, which is limited to the most superficial epidermal layers. There may be a case for increasing current exposure limits. Simulations suggest that appropriately deployed far-UVC will be a fast and effective public health control for inactivating SARS-CoV-2 in an occupied room.