Extreme Exposure to Filtered Far-UVC: A Case Study^†.

Area of Science:

• Photomedicine
• Dermatology
• Microbiology

Background:

• Far-ultraviolet (Far-UVC) devices emitting at 222 nm are marketed for SARS-CoV-2 inactivation.
• There is a lack of human safety data for these devices.
• Proof-of-concept human self-exposure studies are needed to inform research and public discussion.

Purpose of the Study:

• To conduct a rapid, proof-of-concept human self-exposure study using a filtered Krypton-Chloride (KrCl) far-UVC system.
• To assess the safety of varying radiant exposures on human skin.
• To inform future controlled research and discussions on far-UVC device safety and efficacy.

Main Methods:

• A Fitzpatrick Skin Type II individual was exposed to filtered 222 nm KrCl far-UVC light on their inner forearms.
• Radiant exposures ranged up to 18,000 mJ/cm².
• Skin reactions were monitored, and Monte Carlo Radiative Transfer modeling was employed.

Main Results:

• No visible skin changes or erythema were observed at exposures up to 1500 mJ/cm².
• Transient skin yellowing occurred immediately at 6000 mJ/cm², resolving within 24 hours.
• No erythema was observed even at the highest exposure of 18,000 mJ/cm².

Conclusions:

• Filtering longer ultraviolet wavelengths is critical for ensuring the human skin safety of far-UVC devices.
• The study supports the need for further research into expanding exposure limits for far-UVC applications.
• Expanded exposure limits could enable more efficient viral inactivation.