Safety of 222 nm Band-Pass Filtered Irradiation

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A Review and Analysis of Current Data

Although 254 nm light is the prevalent UV source in current disinfection devices, the SARS-CoV-2 outbreak has focused interest on the potential to instead use 222 nm band-pass filtered (BPF) light for disinfection. Irradiation with 222 nm light is an attractive alternative because, unlike irradiation with 254 nm light, it has been shown that 222 nm light kills bacteria and deactivates viruses without causing DNA lesions, erythema, photo-keratitis and other associated effects of 254 nm light in biological tissue.

The purpose of this paper is twofold: First, to present literature that describes the effects and efficacy of 222 nm light; and second, to propose a new spectral effectiveness value that was calculated based on the reviewed data. Spectral effectiveness is a unit-less quantity capturing the action spectra which measures the minimum dose that causes a biological effect.

Recent studies suggest that tissue damage is not caused by shorter (222 nm) wavelengths, due to reduced penetration depths in live tissue when compared to 254 nm light. While the effects on live tissue are diminished, 222 nm light has increased efficacy for killing bacteria and deactivating viruses. Current safety guidelines do not, however, account for the true 222 nm exposure limits, in part resulting from poorly characterized light sources in heritage publications. We find the historical data taken at 222 nm to be lacking and propose a reexamination herein.