One‐year Ocular Safety Observation of Workers and Estimations of Microorganism Inactivation Efficacy in the Room Irradiated with 222‐nm Far Ultraviolet‐C Lamps

Abstract

Two krypton‐chloride germicidal excimer lamp units (Care222 TRT‐104C11‐UI‐U3, USHIO Inc.) were installed in the examination room of an ophthalmology department. The irradiation dose was set not to exceed the former (i.e., before 2022) threshold limit value (TLV) (22 mJ cm−2/8 h) recommended by the ACGIH. Section 1: The eyes and lids of the six ophthalmologists (5 wore glasses for myopic correction) who worked in the room for a mean stay of 6.7 h week−1 were prospectively observed for 12 months. Slitlamp examinations revealed neither acute adverse events such as corneal erosion, conjunctival hyperemia, and lid skin erythema nor chronic adverse events such as pterygium, cataract, or lid tumor. The visual acuity, refractive error, and corneal endothelial cell density remained unchanged during the study. Section 2: The irradiation of samples placed on the table or floor using the same fixtures in the room (5–7.5 mJ cm−2) was associated with >99% inhibition of φX174 phage and >90% inhibition of Staphylococcus aureus. In conclusion, no acute or chronic health effects in human participants was observed in a clinical setting of full‐room ultraviolet germicidal irradiation by 222‐nm lamp units, and high efficacy in deactivation of microorganisms was determined in the same setting.

Negligible increase in indoor endotoxin activity by 222 nm far-UVC illumination on bioaerosols

“…The data of low UV irradiance (35 mW cm −2 ), which is commonly applied for airborne disinfection, was also included. 19,71,72 We found that for all UV irradiance, the endotoxin activity ratio linearly increased with the UV dose (R 2 = 0.74), supporting that the release of endotoxins was due to photochemistry (Fig. 3a).…”

Far‐UVC Light at 222 nm is Showing Significant Potential to Safely and Efficiently Inactivate Airborne Pathogens in Occupied Indoor Locations

“…Extensive studies in rat eyes by Kaidzu et al (17) concluded that the minimum far-UVC dose to induce corneal damage was far larger than the recommended regulatory limits (see below). A first in-situ study of human eye safety after long term far-UVC exposure was recently published (20), showing no adverse effects after 12-month exposures using multiple endpoints based on slit lamp examinations.…”

222 nm Far-UVC from filtered Krypton-Chloride excimer lamps does not cause eye irritation when deployed in a simulated office environment

“…It has also been argued that the 10 mJcm -2 is incorrect due to the bandwidth of the monochromator used by Pitts in 1973 and the true threshold may be much higher than noted (20,23). In more recent work on Far-UVC, six ophthalmologists exposed to filtered 222 nm Far-UVC in their work environment for more than one year, demonstrated no ill eye effects (24).…”