Exposure of Human Skin Models to KrCl Excimer Lamps: The Impact of Optical Filtering^†

Abstract

Far-UVC radiation is a promising technology that is potentially both effective at killing airborne microbes such as coronaviruses and influenza, and being minimally hazardous to the skin and eyes. Our previous studies on health risks from far-UVC have employed a krypton-chloride (KrCl) excimer lamp, emitting principally at 222 nm, supplemented with an optical filter to remove longer wavelength emissions inherent to these lamps. This study explores KrCl lamp health hazards by comparing filtered and unfiltered KrCl lamps using effective spectral irradiance calculations and experimental skin exposures. Analysis of effective irradiances showed a notable increase in allowable exposure when using a filter. Induction of DNA dimers (CPD and 6-4PP) was measured in human skin models exposed to a range of radiant exposures up to 500 mJ cm −2 . Compared to sham-exposed tissues, the unfiltered KrCl lamps induced a statistically significant increase in the yield of both DNA lesions at all the radiant exposures studied. Conversely, filtered KrCl lamps do not induce increased levels of dimers at the current daily TLV exposure limit for 222 nm (23 mJ cm −2 ). This work supports the use of filters for far-UVC KrCl excimer lamps when used to limit disease transmission in occupied locations.

Extreme Exposure to Filtered Far‐UVC: A Case Study†

“…This is proven further in a recent publication by Buonanno et al . ( 19 ). It is well recognized that it is important, when assessing the hazard from an ultraviolet source, to consider all wavelengths and plot the source spectrum on a logarithmic scale ( 20 ).…”

Computer Modeling Indicates Dramatically Less DNA Damage from Far‐UVC Krypton Chloride Lamps (222 nm) than from Sunlight Exposure

“…In further support of the computer modeling, Buonanno et al demonstrated that CPDs produced by a filtered KrCl excimer lamp were approximately 10–12% of the CPDs produced by an unfiltered source (8). MCRT simulation indicates that the Ushio Care222 (filtered) would produce 7% of the CPD produced by the source from Woods et al.…”

“…Buonanno et al. also demonstrated, in a skin model, limited DNA damage confined to the upper most layers of the skin only from a filtered KrCl lamp: 0.016% of keratinocytes had CPD at TLV which was 730 times less CPD than exposure to 254nm at TLV (8). In contrast, Shih et al showed prolific CPD throughout the epidermis from simulated sunlight exposure at just 80% of the Minimal Erythema Dose (MED) (16).…”

“…This is particularly true in the most critical (in terms of skin cancer risk) basal layer, where the computer modeling estimates that approximately 30 000 h of exposure to the Ushio Care222 at current exposure limits would produce the equivalent number of CPD that would occur from 10 min when the UV Index is 4, typical of morning English sunshine from Spring to Autumn (13). CPD are a type of DNA damage that is specific to UV, and they are more prolific than other markers of DNA damage such as 6‐4PP (8).…”

“…The attraction of this technology is its apparent effectiveness accompanied by a lack of acute skin and eye reactions, even at radiant exposures above the current exposure limits (5, 6). In addition, several studies have now shown that these wavelengths of UVC appear to induce minimal amounts of deoxyribonucleic acid (DNA) damage in the skin and the damage that is induced is limited to the upper‐most non‐proliferating skin cells (7, 8). This suggests that long‐term exposure to these wavelengths is unlikely to be associated with increased skin cancer risk through induction of cyclobutane pyrimidine dimers (CPD) or 6–4 photo‐products (6–4PP) (8, 9).…”