Ultraviolet light can make indoor places safer during an epidemic – if used properly

Ultraviolet light has a long history as a disinfectant and the SARS-CoV-2 virus, which causes COVID-19, is rendered readily harmless by UV light. The question is how best to harness the UV light to fight the spread of the virus and protect human health as people work, study and work indoors.

The virus spreads in many ways. The main route of transmission is through person-to-person contact via aerosols and droplets when an infected person breathes, interacts, sings or coughs. The virus can also be transmitted when people touch their faces immediately after touching infected surfaces by infected individuals. This is of particular concern in healthcare settings, retail locations where people often touch counters and merchandise, and in buses, trains, and planes.

As an environmental engineer who studies UV light, I have seen that UV can be used to reduce the risk of transmission through both routes. UV lights can be components of mobile machines, whether robotic or human-controlled, disinfected surfaces. They can be incorporated into heating, ventilating and air conditioning systems or otherwise deployed in airflow to disinfect indoor air. However, UV portals that are meant to disinfect people to penetrate indoors are potentially ineffective and potentially dangerous.

What is ultraviolet light?

Electromagnetic radiation, which includes radio waves, visible light, and X-rays, is measured in nanometers, or millionths of a millimeter. UV radiation has wavelengths between 100 and 400 nanometers, located beyond the violet portion of the visible light spectrum and invisible to the human eye. UV is divided into UV-A, UV-B and UV-C regions, which are 315–400 nanometers, 280–315 nanometers and 200–280 nanometers, respectively.

The ozone layer in the atmosphere filters out UV wavelengths below 300 nanometers, blocking UV-C from the sun before reaching the Earth’s surface. I consider UV-A as the suntanning range and UV-B as the sun-burning range. High doses of UV-B can cause skin lesions and skin cancer.

UV-C has the most effective wavelengths for killing pathogens. UV-C is also dangerous for eyes and skin. Artificial UV light sources designed for disinfection emit light in the UV-C range or a broad spectrum including UV-C.

How UV kills pathogens

UV photons between 200 and 300 nanometers are absorbed quite efficiently by the nucleic acids that make up DNA and RNA, and photons below 240 nanometers are also well absorbed by proteins. These essential biomolecules are damaged by absorbed energy, rendering genetic material inside a virus particle or microorganism unable to replicate or cause an infection, neutralizing the pathogen.

It typically takes very low doses of UV light in this germicidal range to inactivate a pathogen. The UV dose is determined by the intensity of the light source and the duration of exposure. For a given required dose, sources of higher intensity require shorter exposure times, while sources of lower intensity require longer exposure times.

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UV disinfection, which can be performed by robots in this way, minimizes hospital-acquired infections.
Marcy Sanchez / William Beaumont Army Medical Center Public Affairs Office

There is an established market for UV disinfection equipment. Hospitals have used robots that emit UV-C light to disinfect patient rooms, operating rooms, and other areas where bacterial infection can spread. These robots, incorporating True-D and Xenx, enter empty rooms between patients and disinfect high-power UV radiation by moving far and wide. UV light is also used to disinfect medical devices in special UV exposure boxes.

UV is being used or disinfected for test buses, trains and aircraft. After use, UV robots or human-controlled machines, designed to fit in vehicles or aircraft, pass through those surfaces and can transmit light. Businesses are also considering techniques to disinfect warehouses and retail locations.

Ultraviolet light filling the interior of an empty New York City metro car
The New York City Metropolitan Transit Authority (MTA) is testing the use of ultraviolet light to disinfect out-of-service service cars.

It is also possible to use UV to disinfect air. Indoor spaces such as schools, restaurants and shops that have some air flow can install UV-C lamps overhead and are intended to disinfect air on the roof as it rotates. Similarly, HVAC systems may have UV light sources to disinfect air as it travels through duct work. Airlines can use UV technology to disinfect air in aircraft, or use UV lights in bathrooms between uses.

Far UV-C – Safe for Humans?

Imagine that everyone can walk continuously surrounded by UV-C light. This will kill any aerosolized virus entering the UV area around you or will come out of your nose or mouth if you were infected and shed the virus. The light will also disinfect your skin before your hands touch your face. This scenario may technically be possible someday soon, but health risks are a significant concern.

As the UV wavelength decreases, the photon’s ability to penetrate the skin decreases. These short-wavelength photons are absorbed into the top skin layer, reducing DNA damage to actively dividing skin cells at the bottom. At wavelengths less than 225 nanometers – the far UV-C region – UV appears to be safe for skin contact at doses below the risk levels defined by the International Committee on Non-ionizing Radiation Protection.

Research is confirming these numbers using a mouse model. However, little is known about exposure to the eyes and injured skin at these remote UV-C wavelengths and people should avoid direct contact above safe limits.

Research suggests that UV-C light may be capable of killing pathogens without harming human health.

The promise of remote UV-C for safely disinfected pathogens opens up many possibilities for UV applications. This is also due to some premature and potentially risky uses.

Some businesses are installing UV portals that irradiate people on the go. While this device may not cause too much damage or skin damage in the few seconds it runs through the portal, low doses and the ability to disinfect clothing will also not be effective to reduce the transmission of any virus.

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Most importantly, eye protection and long-term exposure have not been well studied, and these types of devices must be regulated and validated for effectiveness before being used in public settings. There is also a need to understand the effect of continuous germ radiation exposure on the overall environmental microbiome.

More studies about remote UV-C show that exposure to human skin is not dangerous and if there is no harm from contact with the eyes, it is possible that remote UV-C installed in public places The Lite system could support efforts to control the transmission of viruses. For SARS-CoV-2 and other potential airborne viral pathogens, today and in the future.

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