There's a lot of UVC disinfection equipment out there, and each product comes with a unique set of technical specifications. These technical specifications are important because they indicate the effectiveness of the germicidal UV product you're considering purchasing, and whether or not that product will work specifically against Coronavirus.
Whether or not a product will be effective against Coronavirus is dependent on a few factors: the length of time the virus is exposed to UV, the intensity of the irradiation, and the wavelength of the UV radiation.
With that in mind, here are a few things to look out for when purchasing germicidal UVC equipment.
UV irradiation intensity
Calculating UV dosage based on light energy
UV Intensity measures the “amount” of UV energy reaching the surface you are disinfecting.
It is measured in the units of millijoules per square centimeter (mJ/cm2), which is energy received per unit area in a given time.
The “dose” of UV Irradiation required for a space is essentially how long the UV light should operate for.
This dose is calculated based on the UV Intensity and the size of the surface or the volume of air you are disinfecting.
The higher the UV irradiation intensity, the less time is required for the UV light to disinfect the surface or volume of air.
Testing done at Boston University's NEIDL laboratory showed that a dose of 5mJ/cm2 resulted in a reduction of 99% of the SARS-CoV-2 virus in 6 seconds at a distance of 1 meter, while a dose of 22mj/cm2 will result in a reduction of 99.9999% of the virus in 25 seconds at 1 meter.
Wavelength
The most effective part of the spectrum
Wavelengths in the ultraviolet band known as “UVC” (200-280nm) have been shown to be the most effective for disinfection.
UVC light at the specific wavelength of 253.7nm has been proven to damage the viral deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) so that the virus cannot reproduce.
Shorter wavelengths, like 207–222 nm (sometimes called “far UVC”) are believed to damage the proteins on the surface of the virus that it needs to attach to human cells, but germicidal UV products at this wavelength, often intended for use around people, need more testing to prove their effectiveness and confirm that there are no long term health effects as a result of exposure.
UVC disinfection equipment at 253.7nm will be the most effective for mitigating Coronavirus transmission in the air and on the surfaces in your space.
Air cycle rate
How air flow factors into dosage requirements
Air cycle rate of UV Air disinfection carts is dependent on a couple factors: UV irradiation intensity and fan speed.
UV irradiation needs to be intense enough to inactivate the virus.
In order to effectively inactivate Coronavirus with UVC light, the virus must be “hit” by the light for a minimum amount of time.
A higher fan speed isn’t necessarily the key to faster air disinfection, because the air may be flowing through at too high of a rate to receive accurate disinfection by the UV light.
Wavelength’s air disinfection products are specified to result in an an 8-log reduction of Coronavirus, or 99.999999% of the virus, based on irradiance within the chamber and air speed through.