UV disinfecting lamps have been the hot topic these days in the fight against COVID-19. Many hospitals and long term care facilities have been using UVC disinfecting lamps in the form of upper room germicidal UV lamps (GUV), in ducts, stationary units or mobile robotics units to disinfect their rooms against bacteria and viruses.
The UV radiation is divided into four parts which are Vacuum UV (100-200 nm), UVC (200-280 nm), UVB (280-315 nm) and UVA (315-400 nm). The radiation received on the surface of the Earth from the Sun only contains UVA and UVB. The UVC part is completely absorbed by the ozone layer and the ionizing vacuum UV radiation is already absorbed by Nitrogen and Oxygen in the upper atmosphere. Bacteria and viruses have not been exposed to UVC radiation and as a result upon exposure from an artificial UVC lamp, the bacteria get killed and the viruses get deactivated through the action of UVC on their DNA.
UVC radiation is hazardous if not properly installed and if the proper precautions are not taken. This article attempts to describe the safety measures that needs to be taken to protect our skin and eyes against UVC and also to compare the hazardous effect of UVC with UVB and UVA radiation.
As far as skin is concerned, the accidental exposure to UVC radiation will cause absorption of the radiation in the outer layers of the skin including outer epidermis and can not make it to the deeper layers of the skin where news cells are constantly created (Reference 1). In other words the penetration depth of UVC radiation in the skin is quite small. UVA and UVB radiation can penetrate much deeper into the skin and can reach the internal layers of the skin. Therefore as far as the possibility of skin cancer is concerned, UVA and UVB are more dangerous than UVC. In fact the order of increasing penetration of UV light increases with UV wavelength. Therefore UVA penetrates the skin more than UVB and UVB in turn penetrates more than UVC. Figure 1 shows the scenario
Figure 1: Penetration of UV rays in the skin (Reference 2)
The effect is reddening of the skin which is called Erythema and is more severe in the case of UVB than UVC which is like a mild transitory sunburn. Figure 2 shows the scenario.
Figure 2: Reddening of the skin due to UV exposure
When it comes to eye exposure, because the eyes have no outer protective layers, they are the most susceptible organ to UV damage. Upper room germicidal lamps have a safety limit of 6.0 mJ/cm2 and exceeding this Threshold Level Value (TLV) in the lower room will cause a painful irritation of the cornea which is similar to a severe exposure in a sunny day especially from water or snow. There will be a painful damage but it will last only for a few days. Corneal shedding will eventually cure the pain after a few days. The effect is like having sand in the eyes and is transitory. Figure 3 shows the scenario,
Figure 3: Eye irritation due to UVC radiation
As for preventive measures against UVC exposure, the following can be mentioned
· When working with UVC stationary units or wands the eyes should be covered with a glass or plastic shield and one should wear nitrile gloves. The rest of the body should be covered with tightly woven fabric so that no skin is exposed.
· For Upper room GUV warning signs should be installed so the repair personnel should not accidentally expose themselves.
· For Air Handling Units (AHU) interlocks should be installed so the lamps in the ducts will be turned off automatically for repair personnel.
· In the case of full room disinfection the room should be completely emptied of people. When this is not possible barriers should be set up in parts of the room where the occupants do not get exposed.
· If it is not possible to set up barriers in a room where a UVC lamp is being used, proper Personal Protection Equipment (PPE) should be worn by occupants during the disinfection process.
· It is necessary to understand that mercury lamp which is the most common type of UVC lamp with an emission wavelength of 253.8 nm can be shielded by glass or plastic. Certain other types of UV disinfecting lamps such as Xenon lamps have continuous emission that covers both UVC and UVB regions. Only simple glass can not stop UVB radiation, so special coated glass should be used to protect against UVB.
Finally, to give a better idea about the proper Personal Protection
Equipment to work with UVC radiation present in the room at the eye level,
figure 4 shows the proper attire.
Figure 4: PPE for working with UVC
As seen in the figure the eyes and face are completely protected with the glass shield, hands are protected by nitrile gloves and the rest of the body is covered with a uniform so that there is no chance of exposure to bare skin.
1- IES photobiology committee report Germicidal Ultraviolet ( April 15, 2020).2- https://www.fda.gov/radiation-emitting-products/tanning/ultraviolet-uv-radiation