Although in India, we are still busy with encountering the second wave of Corona, scientists have started saying that the third wave is inevitable. Worldwide, the medical and pharmaceutical industry experts have been working relentlessly to find ways to defeat the dreadful SARS-CoV family of viruses. Under such circumstances, the lighting industry too has been playing a major role in mitigating the rate of spread of the killer viruses.
Use of Ultra Violet Germicidal Irradiation (UVGI) to control the spread of infectious diseases is not a new concept. Way back in 1845, it was understood that microorganisms respond to light. Later in 1877, Downes and Blunt noticed that – when test tubes containing Pasteur’s solution are exposed to sunlight, the multiplication rate of microorganisms is slowed down. With enhanced exposure, the test tubes remained bacteria-free for several months. Later the observation was verified by many other scientists.
Classification of Ultra Violet rays
Ultra Violet (UV) ray is a spectrum of light just below the visible light range. It is a form of electromagnetic energy. In nature, the sun produces enough amount of UV ray. The human eye cannot perceive UV rays, but some insects like bumblebees can see them.
However, according to WHO (World Health Organisation), “The three types of UV radiation are classified according to their wavelengths. They differ in their biological activity and the extent to which they can penetrate the skin. The shorter the wavelength, the more harmful is the UV radiation. However, shorter wavelength UV radiation is less able to penetrate the skin.
The UV region covers the wavelength range 100-400 nm and is divided into three bands: UVA (315-400 nm), UVB (280-315 nm) and UVC (100-280 nm). Short-wavelength UVC is the most damaging type of UV radiation. However, it is completely filtered by the atmosphere and does not reach the earth’s surface.
Lighting industry and UVGI
For quite a long time, low-pressure mercury discharge lamps were used in UVGI applications. These lamps emit shortwave ultraviolet-C (100 – 280 nanometre) radiation. It has been found that at 254 nanometre (nm), Ultra Violet radiation kills or inactivates the DNA (Deoxyribonucleic Acid) of the microbes. In due course LEDs have mostly taken up the low-pressure mercury discharge lamps – and now the market is flooded with such lamps and sterilization devices built on them.
Technically, absorption of a photon forms pyrimidine dimers (which are molecular lesions formed from thymine or cytosine bases in DNA via photochemical reactions) between adjacent thymine bases and makes the microbe incapable of replicating.
After the discovery of SARS-CoV 2 virus, a very natural question occurred to many people whether Ultraviolet-C Radiation will be effective on this virus. Let us see some important items of information that the US Food and Drug Administration (FDA) shares in this regard.
UVC lamps to inactivate the SARS-CoV-2 coronavirus
As per FDA, “UVC radiation is a known disinfectant for air, water, and nonporous surfaces. UVC radiation has effectively been used for decades to reduce the spread of bacteria, such as tuberculosis. For this reason, UVC lamps are often called ‘germicidal’ lamps.
UVC radiation has been shown to destroy the outer protein coating of the SARS-Coronavirus, which is a different virus from the current SARS-CoV-2 virus. The destruction ultimately leads to inactivation of the viruses.
UVC radiation may also be effective in inactivating the SARS-CoV-2 virus, which is the virus that causes the Coronavirus Disease 2019 (COVID-19). However, currently there is limited published data about the wavelength, dose, and duration of UVC radiation required to inactivate the SARS-CoV-2 virus.
In addition to understanding whether UVC radiation is effective at inactivating a particular virus, there are also limitations to how effective UVC radiation can be at inactivating viruses, generally.
Direct exposure: UVC radiation can only inactivate a virus if the virus is directly exposed to the radiation. Therefore, the inactivation of viruses on surfaces may not be effective due to blocking of the UV radiation by soil, such as dust, or other contaminants such as bodily fluids.
Dose and duration: Many of the UVC lamps sold for home use are of low dose, so it may take longer exposure to a given surface area to potentially provide effective inactivation of a bacteria or virus.
UVC radiation is commonly used inside air ducts to disinfect the air. This is the safest way to employ UVC radiation because direct UVC exposure to human skin or eyes may cause injuries, and installation of UVC within an air duct is less likely to cause exposure to skin and eyes. There have been reports of skin and eye burns resulting from improper installation of UVC lamps in rooms that humans can occupy.”
UVC lamp for disinfection purposes at home
Nowadays, there is a plethora of UV lamp-based devices in the market, which are targeted towards disinfection of homes and public places, for example, Safeology UVC Tower. However, handling those needs proper knowledge and utmost care – as, in any case UV rays are harmful to human bodies.
But FDA cautions, “Consider both the risks of UVC lamps to people and objects and the risk of incomplete inactivation of virus.
Risks: UVC lamps used for disinfection purposes may pose potential health and safety risks depending on the UVC wavelength, dose, and duration of radiation exposure. The risk may increase if the unit is not installed properly or used by untrained individuals.
Direct exposure of skin and eyes to UVC radiation from some UVC lamps may cause painful eye injury and burn-like skin reactions. Never look directly at a UVC lamp source, even briefly.
Some UVC lamps generate ozone. Ozone inhalation can be irritating to the airway.
UVC can degrade certain materials, such as plastic, polymers, and dyed textile.
Some UVC lamps contain mercury. Because mercury is toxic even in small amounts, extreme caution is needed in cleaning a lamp that has broken and in disposing of the lamp.
Effectiveness: The effectiveness of UVC lamps in inactivating the SARS-CoV-2 virus is unknown because there is limited published data about the wavelength, dose, and duration of UVC radiation required to inactivate the SARS-CoV-2 virus. It is important to recognize that, generally, UVC cannot inactivate a virus or bacterium if it is not directly exposed to UVC. In other words, the virus or bacterium will not be inactivated if it is covered by dust or soil, embedded in porous surface or on the underside of a surface.”
Although application of UVGI is a well-established method of disinfecting the surfaces, it is never cent per cent reliable – as the viruses covered under dust or any other thing may not be inactivated by this method. As UV rays are harmful to human bodies, proper knowledge and training are necessary to handle such devices. Lot more research works are essential to confirm the exact parameters of UVC radiation required for complete inactivation of the SARS-CoV-2 virus.
By P. K. Chatterjee (PK)