UV lighting in building infection control: Can passive light safely kill coronavirus?
August 19, 2020
August 19, 2020
Gauging wider application of light radiation in combating the COVID-19 pandemic
In the modern industrialized world, we use electromagnetic radiation (light) as a tool for disinfection and germ control. The healthcare industry commonly employs ultraviolet (UV) radiation for its ability to penetrate and neutralize RNA/DNA of bacteria, viruses, and other pathogens. This UV light is known as germicidal ultraviolet (GUV). Now, as a result of the coronavirus pandemic, GUV is attracting interest for its application as a passive sanitizing design feature that can be used for reducing transmission risk within buildings.
Doctors have used UV light in germicidal sterilization for more than 100 years. The Danish physicist Niels Finsen developed treatments utilizing UV light to combat microbial infections such as skin tuberculosis, achieving an 83% cure rate. He received the Nobel Prize for his work with UV treatments in 1903.
UV light is applied in the control of pathogens and microbes in water treatment, surface disinfection, and within ventilation systems. GUV is a mainstream tool for disinfection. Traditionally, the healthcare sector has mostly used this GUV disinfection technology. With its virus-killing possibilities, designers are looking at applying GUV in other settings such as offices, schools, gymnasiums, and other public places. Of course, the idea of a passive light system that kills the virus is attractive, but is the technology safe?
Is it safe to use powerful UV light in occupied areas? Published research indicates that UV-C light (200-222nm) may be effective at neutralizing bacteria while causing minimal damage to human tissue. Manufacturers and mainstream media are referencing these studies to advocate for the use of UV products inside occupied spaces.
As technical engineers and designers with extensive practical experience, we recognize the need to learn more. We know that 250nm UV-C is harmful to human cells and we are concerned that 220nm wavelength radiation could be dangerous to humans. Given the risks associated with human exposure to UV, we feel that it’s a bit too soon to jump to conclusions regarding exposure safety. We need to see more research and evidence that 220nm can safely be used around people at high enough doses to disinfect before recommending it.
The idea of a passive light system that kills the virus is attractive, but is the technology safe?
There are, however, several established and safe applications of UV light for disinfection of air. We install UV lamps (typically 254nm) within ductwork systems and air-handling equipment. Longitudinal lamps inset within return air ductwork and lamps directed at cooling/heating coils provide effective sterilization and enhance air quality within buildings.
Additionally, we use GUV to disinfect upper air in occupied spaces and by robots to treat surfaces in unoccupied spaces. The upper air system irradiates with GUV above standing head height so that the radiation does not meet humans and can therefore be used in an occupied space. Robots can only be deployed in unoccupied spaces. Both are widely accepted technologies and have been used in healthcare settings for many years but are rarely deployed in other building types.
There are some downsides to this technology. Over time, the use of GUV can degrade many materials, causing them to fade or turn brittle. As we said, GUV can’t come in direct contact with humans. Also, GUV kills indiscriminately, so not only does it kill the bad bacteria but also good bacteria that our systems need to thrive. As soon as we switch off the GUV the disinfection stops. Germs can start to build again and will continue until the next cycle of GUV disinfection.
Our team is excited about another technological development that can be used for disinfection because people can be exposed to it safely. Research shows that continuous light disinfection using 405nm wavelength is effective against many of the bacteria of concern for healthcare-associated infections.
Narrow band 405nm light appears purple (sometimes described as indigo, violet, or lavender). Many studies have found it effective killing the bacteria contributing to hospital acquired infections (HAIs). This light, at the edge of the visible spectrum, doesn’t hurt humans. Most of us don’t feel “normal” working in a room with colored light, so the single band 405nm light tends to be used in unoccupied spaces even though it’s perfectly safe for people. We can also mix the narrow band 405nm light with white light, so the color is not apparent. The white light version of 405nm light is virtually undetectable compared to normal white light. Fixtures that incorporate 405nm light tend to require more energy but are likely to operate within today’s energy standards.
We have yet to see this technology (available as an LED lamp) tested with coronaviruses, but there is research showing it is effective with norovirus when the virus is in organically rich material such as saliva. This suggests it could be effective in combating the coronavirus, which we know is spread through contact with saliva. What makes 405nm light most promising for us, is that it can be used in any space even when people are present. We can deploy this passive technology in virtually any public space to work behind the scenes while people go about their normal daily lives.
For now, we are keeping a keen eye on the marketplace for emergent light products in passive disinfection that are backed by solid research.