With the economy still hobbled by COVID19 and the cost and timing of routine universal testing or a reliable vaccine both still uncertain, it’s urgent that we find safe, cost-effective ways to eliminate airborne viruses from commercial and residential spaces. So, it’s exciting to read new research just published in Nature Scientific Reports showing that more than 99.9 percent of coronaviruses present in airborne droplets were killed when exposed to a particular wavelength of ultraviolet light that is also safe to use around humans.
Based on this new study at Columbia University, continuous airborne disinfection with far-UVC light at the current regulatory limit could greatly reduce the level of airborne virus in indoor environments occupied by people.
Conventional germicidal UVC light with a 254 nm wavelength can be used to disinfect unoccupied spaces such as empty hospital rooms or empty subway cars. However, direct exposure to these conventional UV lamps is not possible in occupied public spaces, as this could be a health hazard.
To continuously and safely disinfect occupied indoor areas, researchers at Columbia University’s Irving Medical Center have been investigating far-UVC light with a 222 nm wavelength, which cannot penetrate the tear layer of the eye or the outer dead cell layer of the skin. Therefore, it cannot reach or damage living cells in the body.
The researchers had previously shown that far-UVC light can safely kill airborne influenza viruses. The new research extends this research to all coronaviruses, including the SARS-CoV-2 virus that causes COVID-19.
In the study, the researchers used a misting device to aerosolize two common coronaviruses. The aerosols containing coronavirus then flowed through the air in front of a far-UVC lamp. After exposure to far-UVC light, the researchers tested to see how many of the viruses were still alive.
The researchers found that more than 99.9 percent of the exposed virus had been killed by very low exposure to far-UVC light.
Based on their results, the researchers estimate that continuous exposure to far-UVC light at the current regulatory limit would kill 90 percent of airborne viruses in about 8 minutes, 95 percent in about 11 minutes, 99 percent in about 16 minutes, and 99.9 percent in about 25 minutes.
Notably, since SARS-CoV-2 is largely spread via droplets and aerosols that are coughed and sneezed into the air it’s important to have a tool that can safely inactivate the virus while it’s in the air, particularly while people are around.
Because it’s safe to use in occupied spaces like hospitals, buses, planes, trains, train stations, schools, restaurants, offices, theaters, gyms, and anywhere that people gather indoors, far-UVC light could be used in combination with other measures, like wearing face masks and washing hands, to limit the transmission of SARS-CoV-2 and other viruses.