Far UV-C in the 200 – 225 nm range, and its potential for disinfection applications
UV-C radiation in the wavelength range 200 – 225 nm (i.e., ‘far UV-C radiation’) has received public attention for claims of disinfection capabilities and safety of human skin and eye exposure; this is contrasted to ‘conventional’ germicidal ultraviolet irradiation (UVGI) in the wavelength range 240 – 280 nm, which is well accepted as an effective disinfectant but also known to be hazardous to human skin and eyes under direct exposure. Lamp technologies covering both spectral ranges have existed for many decades, though far UV-C has not been widely applied. Laboratory studies have shown that far UV-C sources can inactivate microorganisms at comparable rates to, or faster than, conventional UVGI sources.
The two technologies share common disinfection pathways, where direct photolysis of DNA/RNA and/or proteins inactivates the target pathogen. Radiation across the UV-C spectrum is a known disinfectant, though the volume of research on far UV-C disinfection is substantially smaller than that of mature UVGI technology. ‘Skin safe’ claims for far UV-C are based on the concept that the higher energy radiation at these shorter wavelengths is absorbed by outer protective skin cells (stratum corneum), or in the case of eyes, the outer tear layer, and therefore does not reach susceptible tissue to cause damage.
By contrast, bacteria and viruses do not have such shielding and are directly exposed. Skin and eye safety claims are supported by several studies in live mouse models, mouse tissue, and human tissue models with promising findings; though more work is required, the evidence suggests the absence of conventional skin damage indicators that would typically result from UVGI.
To date, no clinical or long-term studies of human exposure have been conducted and the effect on injured skin or eyes is unknown. Such work is essential in determining the safety of this technology before any wide-spread application While initial findings are positive, further investigations are required on any secondary impacts of the technology when used in the presence of humans.
For instance, the potential for unexpected photochemical reactions, e.g. in cosmetics or clothing; the potential for generation of ozone during continual operation or within enclosed spaces; and determination of threshold limit values (TLVs) for safe daily exposure are all topics that need to be better understood. Far UV-C is a promising technology application, though currently in the early stages of research.
There is not yet sufficient evidence to support widespread application where direct human exposure is anticipated. The IUVA recommends that far UV-C not be implemented as an unshielded disinfection technology until sufficient evidence for safety is presented, and suitable protocols for application are established.
This white paper was produced by a working group of the International Ultraviolet Association (IUVA), an organization established to provide a forum for the discussion of all scientific and technological issues that relate to the use of ultraviolet light. This particular working group consists of IUVA members ranging from UV equipment manufacturers, scientists, engineers, to consultants, and members of the medical profession. The objective of this work is to provide an impartial presentation of the available facts on the technology commonly referred to as ‘far UV-C’ and an analysis based on expert interpretation and knowledge of the field of UV disinfection, safety, and public health. The IUVA does not endorse any private entities discussed herein, nor will it pass comment on the accuracy or validity of claims made by individual vendors.
Lead author: Rich M. Simons Co-authors: Ernest R. Blatchley III, Karl G. Linden This document was reviewed by a diverse committee of International Ultraviolet Association (IUVA) members to ensure scientific accuracy and a fair representation of general consensus; however, it does not necessarily reflect a unanimous agreement from all IUVA members.
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