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Ultraviolet radiation has been used as a microbicide for more than a century. From water purifiers to laboratory equipment, UV radiation has wide utility in rendering fluids and surfaces microbe-free.
However, its usage became limited to applications that did not involve direct human exposure because of its adverse effects on the skin and eyes. Although conventional near-UV radiation is indeed harmful to humans, it has been shown in recent years that far-UV radiation, contrary to intuition, is both an effective germicide and largely non-harmful to humans.
However, that research, although well received in scientific circles, has been largely ignored by non-scientists, leading to grossly misleading statements such as this one quoted in The Washington Post: “Of the three types of ultraviolet light, UVC is the deadly one, long-established for water and air sanitizing, but also one that people should never fool with. The invisible light is highly carcinogenic, with disinfecting results that vary widely in professional settings depending on the setup.”
Such apprehensions are at odds with this rigorous research study published in the prestigious journal Nature Scientific Reports in February 2018. Although UV radiation is already being utilized to battle Covid-19, people are critical of its employment for human disinfection purposes such as hand sanitization.
Far-UVC light (wavelength 207-222 nanometers) is effective in inactivating microbe cells, without harming the skin, over a variety of dose sizes and distributions, both acute and chronic. Far-UVC radiation cannot penetrate even the outer, non-living strata of human skin or eyes; however, because microbial pathogens have dimensions of microns (micrometers) or less, far-UVC can permeate and render them inactive.
The aforementioned paper showed that far-UVC light also efficiently inactivates airborne aerosolized viruses, with a mere dose of 1.8mJ/cm2 (millijoules per square centimeter) of 222nm light inactivating 95% of aerosolized H1N1 influenza virus. Note that even by the old guidelines of the American Conference of Governmental Industrial Hygienists (ACGIH), which are inconsiderate of different effects of different frequencies of UV radiation, a dosage of 3mJ/cm2 in an eight-hour period is fixed as the safety limit.
It has also long been established that UV light under 285nm can also efficaciously attenuate both drug-sensitive and multi-drug-resistant bacteria, as well as render various strains of viruses ineffectual.
UV radiation is mutagenic and breaks a variety of molecular bonds. It also interferes with certain cellular processes, hinders cell division, and damages genetic material in unicellular pathogens including viruses. However, being a carcinogenic and cataractogenic, conventional UV radiation was deemed unsuitable for everyday sanitation purposes to the point that the safety and efficacy of UVC radiation weren’t even distinctly explored.
In the 2018 paper, the researchers state: “Continuous very low dose-rate far-UVC light in indoor public locations is a promising, safe and inexpensive tool to reduce the spread of airborne-mediated microbial diseases.” The study proved the efficacy of far-UV radiation in inactivating airborne, aerosolized viruses with aerosol droplets the size of those commonly emitted by humans during coughing and exhalation – which happens to be the exact nature of the spread of the Covid-19 contagion.
Even very small dosages of radiation achieved log 1 and log 2 reductions. Moreover, the study also prospected far-UV as a mass-scale infrastructural public safety solution.
According to David J Brenner, professor of radiation biophysics at Columbia University, the benefits of using far-UV for germicidal purposes over near-UV were threefold: It poses an insignificant risk of skin cancer and other bodily harms, it is quite effective against viruses, and it is potentially effective against new and emerging strains of infectious pathogens.
According to Brenner, sources emitting germicidal far-UV radiation could be cost-effectively mass-produced and subsequently deployed in human environments and spaces. This discussion hosted at the David J Brenner Center for Biological Research at Columbia University shows that the efficacy of UVC radiation in curbing coronaviruses has been known since 2017.
Governments could work on developing a small handheld device with which individuals could irradiate themselves with a very brief and optimally intense split-second burst of UV radiation, in accordance to safety norms.
Note that existing dosage safety limits are conservative and might heavily err on the side of caution, since they all precede the research which revised the safety of far-UV radiation. They are mostly either indiscriminate to the frequency of radiation (same limit irrespective of the frequency), or are obtained by means of indolent extrapolation.
The ideal solution is a gadget that automatically turns itself off so that it can only be triggered to deliver a prescribed, norm-compliant, fixed dosage once every few hours. This time period may be ascertained and revised after further investigation into the acceptable irradiation and exposure duration of far-UV radiation on the human body, which in light of recent research is likely to be much higher than previously suggested.
In any case, the effectiveness of UV radiation is eliminating coronaviruses is well established and therefore promising in eliminating the novel coronavirus that causes Covid-19.
A device that emits a calculated dose of UVC radiation would go a long way in habituating the population of hand-sanitization. Such dry hand-sanitizers that involve no consumables and contact could prove very handy. Their convenience and safe dosage delivery would facilitate and encourage hand-washing by precluding the usual bother of conventional means of manual disinfection.
Installing such devices at public places could vastly alleviate the public health hazard posed by contagious ailments.