Covid-19: Is UV light safe as a disinfectant?
When using ultraviolet lights to disinfect items or surfaces, it’s important to know what works and what doesn’t
Earlier this month, when the World Health Organization (WHO) acknowledged that there was “emerging evidence" of the airborne spread of the novel coronavirus, especially in indoor settings, the focus shifted back to a disinfection method that has proved polarizing: ultraviolet (UV) lights.
Certain studies support the efficacy of UV lights in disinfecting some living and working spaces and day-to-day items. Others maintain that any direct exposure of the human skin to these lights can be a health hazard. So what works and what doesn’t?
To answer this question, it’s key to understand the different types and wavelengths of UV lights: UVA, UVB and UVC. Both UVA and UVB are wavelengths of UV rays that reach us through sunlight, after being filtered by the atmosphere. According to WHO, the long-wavelength UVA, which covers a range of 315-400 nanometres (nm), accounts for approximately 95% of the UV radiation that reaches Earth’s surface. UVB, which is medium wavelength (in the range of 280-315nm), promotes the production of vitamin D in the human skin. The shortwave-length UVC (in the range of 100-280nm) is considered the most damaging. According to a fact sheet on UV disinfection for covid-19 by the US-based International Ultraviolet Association, UVC light is much “stronger" than normal sunlight and can trigger a severe sunburn-like reaction. Most of the UVC radiation is absorbed by Earth’s ozone layer but it can be produced artificially with UV lamps.
It’s not all bad, however. For, it’s only UVC light that has the capability to kill pathogens or render them inactive. A recent study by researchers at the Columbia University Irving Medical Center showed that more than 99.9% of seasonal coronaviruses present in airborne droplets were killed when exposed to a particular wavelength of ultraviolet light that is safe to use around humans. The study, which was published in the journal Scientific Reports in June, investigated the effects of far-UVC light (in the 254nm wavelength) on two common coronaviruses which are structurally similar to the SARS-CoV-2 virus.
So, is UVC more effective than, say, chemical disinfecting solutions? “Chemical disinfectants have also been recommended by the World Health Organization for disinfecting surfaces, particularly floors. However, these chemicals have residual effects and cannot be used to disinfect many articles like eatables, personal articles like laptop, mobile, watches and so on," says Prof. Naresh Rakha, senior scientific officer at the Indian Institute of Technology, Ropar. “UVC radiations provide physical disinfection and do not have residual effects," he says, adding that UVC radiation has “maximum germicidal effect". People, of course, should not be exposed to it.
Along with his colleague Khushboo Rakha, Prof. Rakha recently designed and conceptualized a prototype of a UVC disinfection unit that uses ultraviolet germicidal irradiation technology. “The ultraviolet C radiations emitted by the special UVC Lamps (act as a) surface disinfectant and (can) inactivate virus, bacteria and other microbes by attacking their DNA, RNA," he explains. Attacking a pathogen’s DNA or RNA effectively ends its ability to reproduce.
Interest in UVC technology, albeit not new, has spurred the innovation of products in recent months. Traditionally, UVC lights have been used to disinfect drinking water, air and pharmaceutical tools, among other things. But covid-19 has forced many to make this technology more accessible to the general user.
“More or less, it is the most convenient way to disinfect. You can put up a (UV) lamp in a room, close it and in 30-40 minutes, the entire room will be safe to use. It could be, say, a good use for hospital beds. There’s huge interest from consumers because of its properties and the speed, convenience with which it can disinfect things," says Prag Bhatnagar, senior vice-president, Havells India Ltd. The electrical equipment company is developing some products on similar lines and expects to launch them in a few weeks, he adds.
Apart from making UVC light products safe, by using sensors that detect human presence and stop the disinfection process automatically, what’s important is the form factor. “How can you make sure you have an innovative form factor (for a product) which is easy to use in households?" says Bhatnagar.
Offices today, for instances, are often shared spaces where people not only work together but share desks, among other items. “In this changed environment (after covid-19), nobody would like to do that. What we can do is have light fixtures that give out normal light in the morning and in the night—during the off hours—they throw UVC light to disinfect the area. These things are difficult to achieve and need to be programmed keeping smart connectivity features in mind," adds Bhatnagar.
In a recent example, UV disinfection robots from Danish company UVD Robots were able to learn the layout of some hospitals in China and detect human presence while performing their tasks. These robots would autonomously disinfect areas where hospital staff was not present.
Some smaller UVC products are available in the Indian market. “We mostly focus on sanitizing our hands but what about something like a mobile phone, which is exposed more to outdoor elements?" asks Pankaj Garg, founder and CEO of online lifestyle accessories brand DailyObjects. Earlier this year, DailyObjects launched a handheld, pocket UVC sterilizer, slightly bigger than a pen, and a multifunctional UV sterilizer that doubles up as a wireless charger. “When we step out of our homes, we also touch so many surfaces: elevator buttons, door handles, etc. The idea behind the pocket UVC sterilizer was to have something that users can carry around," he adds.
Portable or not, Prof. Rakha emphasizes that it’s important to use UVC products carefully, especially in home settings. Any handheld UVC device should never be pointed in the direction of the user. “The most important thing to know is that UVC radiations affect the DNA of all living things, including humans and animals. UV chambers should always be leak-proof, closed boxes. Users must ensure that they or their pets should never be exposed to UV radiations."
FIRST PUBLISHED22.07.2020 | 09:00 AM IST