Background about UV-C and Contaminants

ABOUT UV LIGHTING AND CONTAMINANTS

ABOUT UV-C & COVID-19

“Can UV lighting effectively inactivate the virus responsible for COVID-19?” According to the Illuminating Engineer’s Society (IES) report published April 2020, their answer is “Yes” but under certain conditions.

The most effective UV lighting for inactivating viruses is UV-C lighting. Although UV-C also kills bacteria, facility managers and owners must consider all specifications before making a decision on the type of lighting they need.

For example, while IES found that upper room or air handling systems are the most effective ways to inactivate airborne contaminants, UV-A and UV-B lighting are also useful in killing bacteria in lower room areas.

The article from by Darren Verebelyi, PhD published at CoScientific LLC summarizes the background and benefits nicely as below:

Background

UV light is the part of the electromagnetic spectrum that is right next to the spectrum of visible light that we are familiar with. UV light has a shorter wavelength than visible light but is higher in energy.

After UV light was discovered in 1801 they were termed "chemical rays" because oxidation was accelerated in some materials. This was the first understanding that UV could alter molecules. Organic-based materials such as living cells and plastics are particularly high absorbers of UV and are therefore susceptible to chemical changes. UV is used commercially to detect materials, create chemical reactions, and to disinfect. UV disables microorganisms such as bacteria, viruses, molds, and other pathogens and is therefore widely used to disinfect water, the air in commercial buildings, and surfaces of medical equipment.

spectrum

With wavelength ranges shown in the above diagram, the UVA spectrum accounts for 95% of the UV light from the sun with 5% in the UVB range. All of the UVC light is filtered out by the Earth’s atmosphere. Since UVA and UVB light are naturally occurring, they fall into a complicated category concerning safety since sunlight can do harm to human tissues.

As scientists have learned more about skin cancer and the dangers of eye damage from UV light, that has led us to avoid overexposure and to protect ourselves with PPE such as sunglasses and sunscreen.
On the positive side, UV is beneficial to humans by providing a means for us to produce our own vitamin D by converting the cholesterol in your skin when exposed to UVB light. It's interesting to note that UV exposure produces endorphins with an opioid-like effect and studies suggest that it's biologically addictive even though it can be detrimental by causing cell mutations[1]. The appetite for sunlight drove the invention of artificial sources to bring light indoors with lamps that provide mostly UVA light to dose customers in tanning beds and daylight lamps to treat sleep disorders and jet lag.

It was determined more than 40 years ago that the most effective part of the UV spectrum for disinfection is the UVC band between 100 and 280 nm. UVC is also referred to as ultraviolet germicidal irradiation. To produce this wavelength of light, LEDs are now available. but they are not as cost-effective as the common fluorescent lamp which in its most basic form is a glass tube with a small amount of Mercury (Hg) vapor and two electrodes so that electric current can flow through the plasma. It's highly likely that as a kid your schools use fluorescent lighting and if you're at work right now you can probably see one from your desk. By changing the pressure in the tube and the coating on the inside walls fluorescent lighting can be made to produce different bands of light. High-pressure tubes are widely used to generate light in the blue-green range and low-pressure tubes can be tuned to generate 184 and 254 nm light. Since the 184 nm wavelength is high enough energy to break apart oxygen molecules and form ozone (O3), most germicidal applications use glass which blocks the 184 nm wavelength. Some equipment also uses the ozone to supplement the UVC, but care should be taken to ventilate the area after use since ozone is hazardous to breathing.

There is an interesting subcategory of "far-UVC" light at 222 nm that is becoming relevant since studies have shown that it’s effective while being harmless to humans. Since it’s a shorter wavelength, the energy is absorbed in the outer dead layers of a person's skin. Studies are ongoing and deployment just started in public, but some are concerned that the safety has not been proven well enough for widespread adoption. A popular science article was just published in Discover [2] magazine if you would like to know more.

UV Safety

In addition to premature skin aging and skin cancer from the full UV band of light, UVC, in particular, can cause skin irritation and photokeratitis (snow blindness) with as little as a minute of closeup exposure to a UVC lamp. It's best practice to avoid exposure altogether, but if you must be exposed, covering your skin and using wrap-around eye protection that filters out UV are necessary. The relevant standard for safety glasses is ANSI Z87, with U6 being the best UV protection rating. In the case of accidental exposure, limit your time and distance from the source of light.

"There is no Occupational Safety and Health Administration (OSHA) standard for exposure to ultraviolet light, but the National Institute for Occupational Safety and Health (NIOSH) recommends that the time of exposure to an intensity of 100 microwatts per square centimeter at wavelength 254 nanometers not exceed 1 minute. When averaged over an eight-hour workday, this value is 0.2 microwatts per square centimeter."

References and Credits

[1] Fell, Gillian L et al. “Skin β-endorphin mediates addiction to UV light.” Cellvol. 157,7 (2014): 1527-34. doi:10.1016/j.cell.2014.04.032

[2] https://www.discovermagazine.com/health/are-ultraviolet-sanitizing-lights-safe-for-humans

[3] Akram, Muhammad and Rubock, Paul. "Working Safely with Ultraviolet Radiation-Policy and Procedures." Columbia University, Health Sciences Division, EH&S, 2005

[4] van Doremalen, Neeltje et al. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1, New England Journal of Medicine April 16, 2020 382(16):1564 https://www.nejm.org/doi/10.1056/NEJMc2004973

[5] Bianco, Andrea et al., UV-C Irradiation Is Highly Effective in Inactivating and Inhibiting SARS-CoV-2 Replication (June 5, 2020). Available at SSRN: https://ssrn.com/abstract=3620830

[6] Ansaldi, F., Banfi, F., Morelli, P., Valle, L., Durando, P., Sticchi, L., Contos, S., Gasparini, R., & Crovari, P. (2004). SARS-CoV, influenza A and syncitial respiratory virus resistance against common disinfectants and ultraviolet irradiation. Journal of Preventive Medicine and Hygiene, 45(1-2), 5-8.

[7] Cadnum, Jennifer L et al. “Evaluation of Ultraviolet-C Light for Rapid Decontamination of Airport Security Bins in the Era of SARS-CoV-2.” Pathogens & immunity vol. 5,1 133-142. 22 May. 2020.

[8] https://www.iuvanews.com/stories/pdf/archives/180301_UVSensitivityReview_full.pdf

[9] Russell AD. Ultraviolet radiation. In: Russell AD, Hugo WB, Ayliffe GAJ, eds. Principles and practices of disinfection, preservation and sterilization. Oxford: Blackwell Science, 1999:688-702.

[10] James J. McDevitt, Stephen N. Rudnick, Lewis J. Radonovich, Aerosol Susceptibility of Influenza Virus to UV-C Light, Applied and Environmental Microbiology Feb 2012, 78 (6) 1666-1669; DOI:10.1128/AEM.06960-11

[11] Rutala WA, Kanamori H, Gergen MF, Sickbert-Bennett EE, Weber DJ. Susceptibility of Candida auris and Candida albicans to 21 germicides used in healthcare facilities. Infect Control Hosp Epidemiol 2019;40:380–382.

[12] Advice for the selection and operation of equipment for the UV disinfection of air and surfaces, IUVA, 2020. http://iuva.org/Advice-selection/operation-of-equipment-for-the-UV-disinfection-of-air-and

Comparison of biological entities image licensed per Guillaume Paumier, Philip Ronan, NIH, Artur Jan Fijałkowski, Jerome Walker, Michael David Jones, Tyler Heal, Mariana Ruiz, Science Primer (National Center for Biotechnology Information), Liquid_2003, Arne Nordmann; The Tango! Desktop Project / CC BY-SA; https://creativecommons.org/licenses/by-sa/2.5; Image was cropped and the UVC line position was added.