These UV Devices Could Keep Indoor Air Free of Viruses

These UV Devices Could Keep Indoor Air Free of Viruses

The Boston piano bar where Edward Nardell sings cabaret music would be a perfect setting for airborne disease to spread. But Nardell and his audience are protected from the COVID-19 pandemic by the far-ultraviolet (UV) lights that he had installed to shine down from the ceiling.

FarUV is an emerging form germicidal ultraviolet (GUV) radiation. It is a well-established disinfection technique and growing resource in fighting the virus SARS-CoV-2.

Indoor safety starts with ventilation, but it often can’t stop there, says Nardell (a Harvard T.H. physician and researcher in airborne disease). The Chan School of Public Health is located in Boston, Massachusetts. He explains that ventilation systems that replace air in a space are not powerful enough to protect against coronaviruses or other easily caught diseases.

Systems that actively clean the air in rooms (such as those using HEPA filters) remove more harmful particles. They are also expensive to set up and maintain, noisy and difficult to reach. Multiple devices may be required to cover a room. Donald Milton, an environmental health researcher at University of Maryland School of Public Health, College Park, says that UV air sanitation is the answer.

GUV light can be used to disinfect air with very low air movement. Milton states that GUV light can be used in crowded areas such as schools, hospitals, and restaurants to disinfect air. This is really important in keeping these things under control .”

Gunning for germs

Conventional GUV systems use mercury-vapor lamps. These lamps produce light by passing an electric current through vapourized Mercury. They are similar to traditional fluorescent bulbs. The lamps emit radiation in the UVC band, with a wavelength of around 254 nanometres. The atmosphere filters UVC radiation, so life on Earth cannot withstand it. The radiation causes photochemical damage to nucleic acids, which can inactivate pathogenic viruses and bacteria. However, it does not necessarily kill them.

The lamps are used to disinfect water, clean fruits, vegetables, and sanitize surfaces within spaces like operating rooms. The light from these systems can cause skin and eye damage, so it is best to keep people away. However, this does not mean that it cannot be used in public places. The upper-room GUV method, which was developed decades ago, places the lamps high up in a room and uses rising air currents to kill pathogens far away from people.

This technique works well according to William Bahnfleth (an architect at Pennsylvania State University in University Park whose focus is indoor air quality). Air rises from people, equipment, and existing ventilation. It then passes through the radiation zone of lamps and circulates back into the occupied space.

Although there are no standards for indoor air quality that are universally accepted or enforced, targets are usually expressed in terms of the time a room receives air exchanges per hour. For example, six air changes per hour is the recommended rate for examination rooms in US hospitals. Bahnfleth states that this is a challenge for ventilation systems and requires a lot more energy. An upper-room GUV system, on the other hand, can achieve equivalent levels of air exchange for disinfection purposes at two to three times the rate of a ventilation system while using less energy. “GUV is the only way to get this high number of equivalent air exchanges . It can disinfect such large volumes of air at once .

In an unpublished research that examined various combinations of ventilation and filtration, UV, mask wearing, and UV in a variety of buildings including offices, schools, and hotels, “UV” was the only technology that consistently reduced the risks to acceptable levels, according to Shelly Miller, a mechanical engineering specialist at the University of Colorado Boulder. “UV is an incredibly powerful tool for cleaning the air. We are missing the mark on .”

,” says Shelly Miller.

Riding shorter waves

Upper-room GUV was widely adopted in schools and hospitals following studies1 in the late 1930s and 1940s led by William Wells, a biologist then at the University of Pennsylvania in Philadelphia. Wells and his colleagues demonstrated that upper-room GUV significantly reduced the spread measles in suburban Philadelphia schools. Upper-room GUV is still being used in many tuberculosis units, but its use has declined with the introduction of stronger interventions like vaccines.

Although the GUV’s UVC light from the upper room is very effective, it must be kept away from people. The GUV light can only clean air if it circulates to the top and passes through the GUV light. This leaves pathogens open to new hosts. This limitation might be overcome by shorter wavelengths.

A krypton chloride excimer lamp.
A krypton chloride excimer lamp. Credit: Ewan Eadie

This is because wavelengths below 254 nm don’t penetrate tissues nearly as well, says David Brenner, a physicist specializing in radiological research at Columbia University in New York City. Far-UV light with a wavelength of 222 nm doesn’t reach beyond the layer of dead cells on the surface of the skin or the film of tears on the surface of the eye. Brenner and his colleagues argued that far-UV radiation could kill pathogens, but not damage the skin or eyes, because bacteria and viruses are smaller than these layers. The scientists tested their hypothesis with lamps containing krypton chloride gas, molecules of which release UVC radiation mainly in the 222 nm range under electrical excitation.

The Columbia team originally aimed to improve disinfection in operating room disinfection, but soon realized that far-UV radiation could also reduce the transmission of airborne viruses. In a 2018 study, the investigators showed that more than 95% of influenza viruses in the air were inactivated when they floated past a low-power far-UV lamp2. Brenner’s group had already shown that cells in a 3D human skin model and in mice were basically unaffected by such low doses3, and other researchers found no evidence of eye damage from 222 nm radiation in rats4.

When COVID-19 hit, the Columbia scientists ran analogous experiments on strains of coronavirus similar to SARS-CoV-2, again with good results5. The researchers collaborated with scientists from the United Kingdom to scale up their experiments, including a Leeds University group that had access to a large-sized test chamber for pathogens.

The room-size experiments used Staphylococcus aureus bacteria suspended in the air. This microorganism is relatively easy to analyse and is expected to be more robust against UV radiation than coronaviruses, says Ewan Eadie, a medical physicist at the University of Dundee, UK, and the lead author of a paper6 that outlines the team’s findings. He says, “We had no idea what was going to happen at the end.”

The results were outstanding. Brenner says that the room experienced a rapid drop in pathogen levels. “Our equivalent air changes per hour were really big, well over 100 equivalent changes per hour.”

On the safety side, Brenner and colleagues reported in May that they had exposed hairless mice to the radiation for 66 weeks without detecting any skin cancer7. Their upcoming research will focus on the risk to the eyes, and further investigate the mechanisms of how 222 nm radiation damages pathogens.

Despite promising laboratory tests of far UV disinfection, there are concerns about how the technology will be implemented in busy indoor spaces like schools, hospitals, and restaurants. Eadie states that the laboratories are clean and sterile. “I would like to see real-world data .”

A real-world clinical trial is underway in Nova Scotia, Canada. It examines the use far-UV light in nursing homes to reduce the spread of respiratory viral infections. The controlled study will track the incidence of COVID-19 and other respiratory viral infections among 200 residents, half of whom will use common areas fitted with far-UV lamps. The placebo lights will be identical to the original but with a lower output. The trial began in October 2021 and the results are expected in early 2023.

Nardell, meanwhile, has started to use an airborne-infection research facility in Emalahleni, South Africa, to study COVID-19. The original purpose of the facility was to analyze tuberculosis infection. It has a three-bed Ward, from which the air is transferred to exposure rooms that house animals that can easily contract the disease. In this case, it is hamsters. Nardell states that hamsters are the preferred experimental animal for COVID. The facility will monitor the hamsters for signs and symptoms of sickness to determine if far-UV radiation is more effective than upper-room GUV systems.

But companies don’t wait for peer-reviewed research. Far-UV lamp fixtures have already been introduced to the market and are being installed all over the globe, not just in buildings but also on buses and other infected areas. While some devices can be used at home, Brenner warns that appliances that emit the wrong wavelengths could cause damage.

Although costs of the fixtures vary widely, Nardell says that US$2,000 is a ballpark retail price for a lamp installed by specialists, and the lamps have an expected lifetime of around 15 months if they run continuously. Far-UV lamps that are based on light emitting diodes (LEDs), may eventually be cheaper and more durable than the gas lamps. However, prototype LED far-UV lamps are limited to very low power levels.

In the meantime, Nardell says that in the piano bar where he performs, the far-UV lamps provide the equivalent of 35 air exchanges per hour, probably making it one of the safest venues for singing on the planet. Brenner invited Brenner and his coworkers to the bar for a night of cabaret, without masks, in the hope that the invisible light would protect them. Brenner says, “I was quite nervous and took lots of COVID test over the next week. But I was fine.”

This article is part of Nature Outlook: Pandemic Preparedness, an editorially independent supplement produced with the financial support of third parties. About this content.

References

  1. Reed, N. G. Public Health Rep. 125, 15-27 (2010).

  2. Welch, D. et al. Sci. Rep. 8, 2752 (2018).

  3. Buonanno, M. et al. Radiat. Res. 187, 493-501 (2017).

  4. Kaidzu, S. et al. Free Radic. Res. 53, 611-617 (2019).

  5. Buonanno, M., Welch, D., Shuryak, I. & Brenner, D. J. Sci. Rep. 10, 10285 (2020).

  6. Eadie, E. et al. Sci. Rep. 12, 4373 (2022).

  7. Welch, D. et al. Photochem. Photobiol. https://doi.org/10.1111/php. 13656 (2022).

ABOUT THE AUTHOR(S)

    Eric Bender is a freelance science writer in Newton, Massachusetts, currently working on a book about Boston Harbor. Follow Eric Bender on Twitter

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