Abstract
Far‐UVC devices are being commercially sold as “safe for humans” for the inactivation of SARS‐CoV‐2, without supporting human safety data. We felt there was a need for rapid proof‐of‐concept human self‐exposure, to inform future controlled research and promote informed discussion. A Fitzpatrick Skin Type II individual exposed their inner forearms to large radiant exposures from a filtered Krypton‐Chloride (KrCl) far‐UVC system (SafeZoneUVC, Ushio Inc., Tokyo, Japan) with peak emission at 222 nm. No visible skin changes were observed at 1500 mJ cm−2; whereas, skin yellowing that appeared immediately and resolved within 24 h occurred with a 6000 mJ cm−2 exposure. No erythema was observed at any time point with exposures up to 18 000 mJ cm−2. These results combined with Monte Carlo Radiative Transfer computer modeling suggest that filtering longer ultraviolet wavelengths is critical for the human skin safety of far‐UVC devices. This work also contributes to growing arguments for the exploration of exposure limit expansion, which would subsequently enable faster inactivation of viruses.
Highlights
The severe acute respiratory syndrome coronavirus 2 (SARSCoV-2) is the virus responsible for the current global COVID-19 pandemic
There is roughly 100 times less incident on the basal layer between 240 and 320 nm, when comparing the filtered far-UVC to the unfiltered source. These self-exposure results have indicated that large radiant exposures (“doses”) of 1500 mJ cmÀ2 of filtered far-UVC can be delivered to pale skin without induction of visible changes
A dose of 1500 mJ cmÀ2 is much larger than the 23 mJ cmÀ2 limit of exposure in the International Commission on Non-ionizing Radiation Protection (ICNIRP) guidelines [18]
Summary
The severe acute respiratory syndrome coronavirus 2 (SARSCoV-2) is the virus responsible for the current global COVID-19 pandemic. As of May 2020, the pandemic had resulted in an estimated 3.8 trillion dollars of global consumption losses and 147 million job losses [1]. UVC irradiation is a well-established technology used for the destruction of bacteria and viruses and employed in a range of industries [3,4,5,6]. The established UVC wavelength routinely used for germicidal tasks is the mercury emission wavelength of 253.7 nm, which has been shown to inactivate SARS-CoV-2 and results in acute adverse reactions in the skin and eyes [7, 8]
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