Ultraviolet light can kill microscopic creatures like bacteria and viruses by breaking the molecular bonds in their genetic material. UV light also damages human DNA, causes eye and skin damage and increases our risk of cancer. It turns out, however, that there is a loophole: a specific wavelength of UV light that is safe for humans but can kill coronaviruses both on surfaces and in the air.
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However, there are some problems with using UVC light for disinfection. They need a certain intensity to kill microbes quickly. Because low-power devices are sold to consumers, you need to keep a device like a smartphone in a glowing box for a very long time in order for it to be effectively disinfected – and this requires that all devices are properly exposed to UVC light. The other problem is a little more worrying: germicidal UVC light with a wavelength of 254 nanometers is considered carcinogenic and causes DNA mutations in the skin and eyes. Hospitals are taking extreme measures to use it safely where the average consumer undoubtedly would not.
Experts such as Jim Malley, Professor of Civil and Environmental Engineering at the University of New Hampshire and Founding President of the International Ultraviolet Association, recommend social distancing instead, proper hand washing, masks, and even disinfectant wipes to minimize exposure to Covid-19 – at least for now. Two recent studies, one at Vagelos College for Doctors and Surgeons at Columbia University’s Irving Medical Center and one at Hiroshima University in Japan, found that a very specific wavelength of UVC light – 222 nanometers – does not penetrate the eye’s tear layer can penetrate or the dead layer of cells in the skin that prevents it from reaching and damaging living cells in the human body.
The Columbia University study, published June 2020, found that even low exposure to 222 nanometer UVC light could kill two common coronaviruses (which cause seasonal colds) that had been aerosolized. Exposure to this far-UVC light for about eight minutes killed 90% of airborne coronaviruses. It took about 25 minutes for 99.9% of the viruses to be killed. Last week, another study from Hiroshima University confirmed that far-UVC light is effective at killing SARS-CoV-2 (the virus that causes Covid-19), even though the tests were done in a controlled environment. The researchers exposed a virus culture on a polystyrene plate at a distance of 24 centimeters to a far-UVC lamp, which killed 99.7% of the virus in just 30 seconds.
Despite the tests of success, the Japanese research team believes that further studies of far UVC light must be carried out using real surfaces and environments before it can be used as an effective disinfection tool. Even so, it’s an exciting discovery as far-UVC light can theoretically be used safely in public places, even when people are around. This would also make the manufacture of UVC sterilization devices safer and cheaper for consumers if fail safes (e.g. locking mechanisms) are no longer required.