Public health concerns have peaked due to the Covid-19 pandemic and have intensified efforts to prevent transmission of infections that are completely or partially airborne using environmental controls. One such control, ultraviolet germicidal irradiation (UVGI), has received renewed interest after decades of use in limited settings. With renewed interest, however, come renewed questions, especially regarding efficacy and safety. A long history of investigations exists concluding that UVGI can be safe and highly effective in disinfecting the air and limiting the transmission of a variety of airborne infections. Despite this long history, many infection control professionals are not familiar with the history of UVGI and its mixed results in safety and effectiveness. This narrative will review the history of UVGI for air disinfection, starting with its biological basis, moving to its application in the real world, and its current status.
Ultraviolet light, or UV, is a part of the electromagnetic spectrum with a wavelength ranging from 100 to 400 nanometers. Thus, it is shorter than visible light but longer than X-Rays. There are three classes of ultra-violet light, UV-A, UV-B and UV-C. Each of these classifications represent ranges of intensity, measured in nanometers or nm. UV-A falls in the 315-400nm range and accounts for 95% of the radiation that reaches the Earth. UV-A is used in tanning beds and penetrates the skin’s second layer, which contributes to skin aging and wrinkling. UV-B is in the 280-315nm range and is a shorter wavelength than UV-A. UV-B will damage the skin’s top layers, causing reddening and sunburn. UV-B will burn unprotected skin in as little as 15 minutes and is strongly linked to cancer. The last classification of ultra-violet radiation is UV-C, which falls in the 100-280nm range. UV-C radiation from the sun never reaches the Earth because it is absorbed by the ozone layer. Not usually considered a risk for skin cancer, it is found in mercury lamps and some types of welding torches.
Ultraviolet germicidal irradiation (UVGI) is an established means of disinfection and can be used to prevent the spread of certain infectious diseases. Low-pressure mercury (Hg) discharge lamps are commonly 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 by damaging their deoxyribonucleic acid (DNA). The principal mode of inactivation occurs when the absorption of a photon 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 micro shadows 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 where the use of protective clothing is not required, 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.
UV Light Applications –
UV Cleaning Boxes
UV Cleaning Booths
UV Cleaning Robots
Building Wide UV Arrays
Human UV Exposure
Often the most important regulatory consideration related to widespread use of UV light as a cleaning vehicle is that of human exposure. The effects of prolonged, continuous exposure to UV-C are of some concern due to their shorter, more intense wavelengths.
To develop this document, I researched the subject using Google, YouTube and several scientific papers sourced from NIH, CDC, and others.
Key Finding #1
Ultra-violet light is widely used in healthcare settings to control airborne pathogens.
Key Finding #2
Ultra-violet light as a disinfectant has a long history in the United States.
Key Finding #3
Ultra-violet light is being used in up and coming designs for the cleaning of public spaces.
Figure 1: Ultra-violet light classifications
Figure 2: Upper room UV Lighting in a Surgical Suite.
Figure 3: HVAC UV Light Array
Figure 4: Mass Transit
Figure 5: UV Light Application in A Large Public Area
Ultra-violet light has been used as a disinfectant for many years and with the onset of the Covid-19 pandemic, research of this technology as a tool to fight the spread of viruses is accelerating.
Ultra-violet light can kill living viruses.
Ultra-violet light utilization can be established in many ways.
Ultra-violet light technology is advancing with applications geared toward large public areas.