The CDC recommends we consider using ultraviolet germicidal irradiation (UVGI) as a supplement to help inactivate SARS-CoV-2, especially if options for increasing room ventilation are limited.
Here are some notes on its use and risks, particularly to the eyes. If it is used in a home or school it is important to not look at the light as it can damage the eye. The US National Institute for Occupational Safety and Health recommends that exposure to UVGI (254 nm) be less than 6000 microJ/cm2 (6000 microW approximately = sec/cm2) over a daily 8-hour period on unprotected skin or eyes.
Ultraviolet Germicidal Irradiation (UVGI) is generally considered safe if used properly. Overexposure to 254 nm radiation can readily cause erythema (“sunburn”) to the skin and photokeratitis (“welder’s flash”) to the eyes, but some studies note the long-term health risks are considered to be comparable with common solar UV exposures.
Ultraviolet germicidal irradiation (UVGI) has been used for years to prevent the spread of certain infectious diseases. Low-pressure mercury (Hg) discharge lamps have been used in UVGI applications and emit shortwave ultraviolet-C (UV-C, 100–280 nanometer [nm]) radiation, primarily at 254 nm. UV-C radiation kills or inactivates microbes like bacteria and viruses by damaging their deoxyribonucleic acid (DNA: photon absorption forms pyrimidine dimers between adjacent thymine bases and renders the microbe incapable of replicating.
UVGI can be used to disinfect air, water, and surfaces, although surface disinfection is limited by microshadows and absorptive protective layers. Water disinfection is currently the most advanced and accepted germicidal application. Air disinfection is accomplished via several methods: irradiating the upper-room air only, irradiating the full room (when the room is not occupied or protective clothing is worn), and irradiating air as it passes through enclosed air-circulation and heating, ventilation, and air-conditioning (HVAC) systems. UVGI is also used in self-contained room air disinfection units.
Upper-room UVGI is one of two primary applications of UVGI air disinfection. Designed for use in occupied rooms without using protective clothing, upper-room UVGI uses wall-mounted and ceiling-suspended, louvered/shielded UVGI fixtures to confine the germicidal radiation to the entire room area above people’s heads and greatly minimizes exposure to occupants in the lower room. Effective air disinfection in the breathing zone then depends on good vertical air movement between the upper and lower room, which can be generated naturally by convection, the HVAC system, or low-velocity paddle fans where needed.
The very aspect (photo-toxicity) that makes short-wavelength ultraviolet (UV) radiation an effective germicidal agent also is responsible for the unwanted side effects of erythema (reddening of the skin) and photokeratitis (“welder’s flash” or “snow-blindness”). Overexposure to this short-wavelength UV radiation can produce these unwanted side-effects from a very mild Irritation of the skin and eyes to a rather painful case of photokeratitis. These effects are fortunately transient, since only superficial cells of the eye-the corneal epithelium-and the most superficial layer of the skin-the superficial epidermis-are significantly affected. Normal turn-over of these cells soon erase the signs and symptoms of these effects. Radiant energy in the UV-C band has very shallow penetration depths which account for the very superficial nature of any injury to the skin and eyes from excessive exposure, minimum risk of delayed effects, and at the same time the strong absorption by bioaerosols. Guidelines for human exposure to UV-C must be applied intelligently so as not to limit germicidal efficacy in upper-room ultraviolet germicidal irradiation. This article is protected by copyright. All rights reserved.
Some units combine UVA
blacklights and fluorescent
white lights. Some units have
UVC only. Although the light
is directed away from the
face, full face shields will
protect from stray radiation.
These units are used for
quick detection of stained
The recommended role of ultraviolet germicidal irradiation (UVGI) is to reduce the risk of tuberculosis (TB) transmission in health care facilities. However, excess exposure may result in dermatosis and photokeratitis. In one hospital setting in Botswana, two nurses and one housekeeper complained of eye discomfort, ‘like sand in the eyes’, after working in an administrative office. The following day, one employee noted facial skin peeling. All symptoms resolved over 2-4 days without sequelae. Six weeks later, the syndrome recurred for all three employees. A workplace investigation revealed that the office had been converted from a hospital sputum induction room, and that an unshielded 36-W UVGI lamp was still installed and operational. The on/off switch for the UVGI lamp was immediately adjacent to the fluorescent bulb on/off switch, and did not have a locking mechanism. The US National Institute for Occupational Safety and Health recommends that exposure to UVGI (254 nm) be less than 6000 microJ/cm2 (6000 microW approximately = sec/cm2) over a daily 8-hour period on unprotected skin or eyes. In the office, UVGI measurements at eye level and looking directly at the UVGI lamp ranged from a low of 20.0 microW approximately = sec/cm2 when seated to a high of 49.9 microW approximately = sec/cm2 when standing. These irradiance levels result in allowable exposure times of 300 and 120 seconds, respectively, and are the most likely cause of the clinical syndrome described.