UV-C light

Safely using UV-C light to disinfect indoor spaces

Wednesday, April 20, 2022
By Brent Peckover

With the spread of SARS-Cov-2, the virus that causes COVID-19, many options claim to be capable of addressing airborne pathogens, including devices like ionizers, ozone and hydrogen peroxide emitters, but none of those technologies has been proven, tested, and used to inactivate pathogens for over a century.

The long-term effects of these technologies are unknown and may come with serious risks, calling into question their use in schools, hospitals, and locations with vulnerable populations. There exists one area of technology that has been tested thoroughly and proven to be effective at ensuring safety: ultraviolet-C light disinfection.

How UV-C light disinfection works

On the most basic level, UV light is broken down into three categories, UVA and UVB which create your tan when you visit the beach, and UVC which is mostly filtered out by the upper atmosphere. Very little UVC (100-280 nanometers) light reaches the earth’s surface. As people began to realize the efficacy of UV-C light and looked to harness the power of UV-C light disinfection, which is capable of inactivating 99.9 per cent of pathogens, they turned to the easiest way available to produce UV-C light, which was with mercury lamps.

Unfortunately, mercury is a neurotoxin and because of this, mercury lamps need to be handled with extreme care. If one breaks, the area needs to undergo serious clean-up and all the people near it must follow strict safety protocols to ensure their health and wellbeing.

Furthermore, the 254 nm wavelength of UVC light produced by mercury lamps effectively penetrates the eyes and skin of people and is known to cause acute and chronic eye and skin damage such as photokeratitis, erythema, cataracts, and cancer. As a result, UV-C disinfection systems that use 254 nm light must do so in such a way that humans are not exposed to the UV-C energy. A great example of employing such a strategy is when 254 nm light is used to disinfect dental tools, which must be done inside a self-contained UV-C oven.

Another example of this during the pandemic has been the use of 254 nm light to disinfect subway cars, but only between operations or at night to ensure the cars are unoccupied. Sadly, when the people return to the space, they bring with them the pathogens we are trying to keep out of the space. Due to the exposure issues, the use of UVC light disinfection in occupied spaces has been limited, until now.

Using UV-C light to disinfect occupied spaces

Historically, there have been two strategies to address the safety concerns with using UV-C light to disinfect air in occupied spaces: The first is upper room UV, which involves deploying high power UV-C light into the space above people’s heads, far enough away that they are not being affected by it. The second strategy is in-duct systems, which involves placing a UV-C lamp into the HVAC ductwork, but this method does not address spaces with insufficient air ventilation.

Both upper room UV and in-duct systems typically use hazardous 254nm mercury lamps and only target air disinfection and do not provide any surface pathogen mitigation. Enter Columbia University, where in 2012, a team led by physicist Dr. David Brenner discovered that another wavelength of light within the UVC spectrum – 222 nm – had a similar ability to inactivate pathogens as the traditionally-used 254 nm wavelength, but without the harmful effects on humans.

Through their research, Dr. Brenner and his team found the 222 nm wavelength was being absorbed by the dead skin layer on the body and the tear layer in the eye in a manner that showed no adverse effects to people, yet still effectively inactivated pathogens just as effectively as the 254 nm wavelength. Finally, we have a UV-C light to disinfect occupied indoor spaces, and today there exist products on the market that harness this.

What to look for in a UV-C light disinfection product

With the full potential of UV-C light disinfection now available to the facilities managers who are entrusted with keeping vital spaces safe, what should these professionals be looking for in a UV-C light disinfection product as they aim to leverage the technology? It all comes down to safety, and there are three main factors when deciding which UV-C product to buy. First, any product being considered for a facility should include 222 nm light as it has the advantage of supporting surface disinfection.

Second, ensure that any 222 nm light entering occupied spaces has a tested filter which attenuates the harmful longer wavelengths of 230 nm and greater. And third, it is vital to check that a product has passed all three types of safety regulations required by UL8802, which include:

● Electrical Safety: As a standard for any electronic device, this safety certification is put forward as a demonstration that the device is safe. But this alone isn’t sufficient when it comes to UVC light products.

● Photobiological Compliance: This ensures that products comply with currently accepted maximum allowable exposure limits.

● Control Safety Testing: This ensures that if a fault in the system occurs, the system will fail safely and occupants within the space will not be overexposed to higher than currently accepted levels.

With those safety requirements met, facilities managers can leverage the immense disinfection power of 222nm UV-C light to keep their facilities and everybody who comes through them safer.

Brent Peckover, P. Eng., is the Director of Industrial Applications at Christie Digital, focusing on launching innovative ideas outside of traditional markets and applications.

While spearheading the design and development activities for commercial ultraviolet disinfection products at Christie, Brent has gained insight into how UV-C light disinfects surfaces and air, in addition to understanding the process in which UV-C light inactivates bacteria and viruses at a generic level.

He has more than 20 years of experience designing, building, and installing a variety of systems for clients around the world. As an aerospace engineer by training, he is used to working in a variety of technical disciplines on projects that benefit from numerical modeling.

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