UV disinfecting lamps have been a hot topic in the fight against COVID-19. Many hospitals and long-term care facilities have been using UVC disinfecting lamps, including upper-room germicidal UV (GUV) lamps, duct-mounted units, stationary units, and mobile robotics units, to disinfect their rooms against bacteria and viruses.
UV radiation is divided into four bands: Vacuum UV (100-200 nm), UVC (200-280 nm), UVB (280-315 nm), and UVA (315-400 nm). The radiation received at Earth's surface from the Sun consists only of UVA and UVB. The ozone layer entirely absorbs UVC radiation, and Nitrogen and Oxygen already absorb ionizing vacuum UV radiation in the upper atmosphere. Bacteria and viruses have not been exposed to UVC radiation; upon exposure to an artificial UVC lamp, the bacteria are killed and the viruses are deactivated by UVC radiation acting 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 needed to protect our skin and eyes from UVC radiation and to compare the hazardous effects of UVC with those of 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 the outer epidermis, and can not make it to the deeper layers of the skin where new cells are constantly created (Reference 1)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 the outer epidermis. It cannot reach the deeper layers of the skin, where new cells are constantly being created (Reference 1). In other words, the penetration depth of UVC radiation in the skin is relatively small. UVA and UVB radiation can penetrate much deeper into the skin, reaching its internal layers. 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 UV light penetration is determined by UV wavelength. Therefore, UVA penetrates the skin more than UVB, and UVB in turn penetrates more than UVC.
The effect is reddening of the skin, called Erythema, which is more severe with UVB than with UVC and resembles a mild, transient sunburn.
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 can cause painful corneal irritation, similar to severe exposure on a sunny day, especially from water or snow. There will be 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.
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 the Upper room, GUV warning signs should be installed to prevent repair personnel from accidentally exposing themselves.
- For Air Handling Units (AHUs), interlocks should be installed so that the lamps in the ducts are automatically turned off for repair personnel.
- For 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 occupants are not exposed.
- If it is not possible to set up barriers in a room where a UVC lamp is being used, occupants should wear proper Personal Protective Equipment (PPE) during the disinfection process.
- It is important to note that the mercury lamp, 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 cannot stop UVB radiation, so special-coated glass should be used to protect against UVB.
As seen in the figure, the eyes and face are entirely protected by the glass shield, nitrile gloves protect the hands, and the rest of the body is covered with a uniform to prevent exposure of bare skin.
References:
1- IES photobiology committee report Germicidal Ultraviolet ( April 15, 2020).
2- https://www.fda.gov/radiation-emitting-products/tanning/ultraviolet-uv-radiation