Now, more than ever, with news that the World Health Organization finally admitted that the SARS-CoV-2 virus is airborne, it is very important that our homes and businesses have clean, safe air to breathe. UVC air sterilizers, as we have discussed before in our previous blog posts, are some of the best tools to fight the COVID-19 pandemic. But not all UVC air sterilizers function the same, and not all UVC air sterilizers are effective.
For a UVC air sterilizing unit to do its job properly, it needs to have the “Functional Trinity”, the three crucial criteria that need to be met to ensure that any infected air that goes in, comes out clean, sterilized, and safe.
The Functional Trinity of UVC: Intensity, Time, and Proximity.
Intensity
According to the International Ultraviolet Association, a dosage of direct UVC light at a wavelength of 254nm (the wavelength necessary to inactivate the virus, as we have previously discussed) is 10-20 mJ/cm². This is said to achieve a 99.9% disinfection rate but under controlled lab conditions. In the real world, viruses can be hidden or shaded from direct UVC light so applying higher dosages, around 1,000-3,000 mJ/cm² is done. This is to achieve the CDC’s disinfection goal which they published online.
But first, what is mJ/cm² and why does this matter when picking out the best UVC air sterilizer for you?
The “J” stands for Joule, a unit of measurement denoting the total amount of energy delivered. In comparison th “W” or Watt, which is the rate of energy delivered.
Think of it in terms of flowing water. Watt is how much water is delivered per unit of time (let’s say, liters per minute) and Joule is the total liters of water delivered after.
1 Joule (1J) is delivering 1 Watt (1W) of energy for 1 second. However, according to the International Ultraviolet Association, the industry measures in smaller increments, ‘milli-Joules’ or mJ, which is a thousandth of a Joule, and ‘milli-Watts’, a thousandth of a Watt.
So to translate what was stated above, to inactivate the virus a UVC light with a 254nm wavelength has to deliver 10 milli-Watts per second, in this case over 1-2 seconds over a 1 square centimeter area, and that is under lab conditions. In the real world, at least 10-30 milliWatts per second, over 300 seconds or 5 minutes over a 1 square centimeter is necessary to be effective. Conversely, if a UVC light can deliver 1,000 mW – 3,000 mW, this time can be cut down to 1 second.
If a UVC air sterilizing unit doesn’t have the proper wattage of UVC bulbs, then their effectiveness could be called into question, because it will not have enough intensity to inactivate the virus.
But as you can see, intensity is just one part of what is necessary in order to properly fight the virus. One element that is just as crucial is…
Time
It’s not enough that the UVC air sterilizer has proper wattage and intensity. If the contaminated air passes too fast and is not given enough time to be exposed to the UVC lamp, then sterilization might not be achieved and the air that comes out of the unit could still have traces of the virus.
While it might not seem like much time, if you look at the requirements above, do note that that is referring to 1 square centimeter of area. To sterilize a larger area, which can accommodate a larger volume of air in this scenario, the intensity of the UVC lamp should work in tandem with the amount of time that the air is exposed to it to ensure that the viruses in the treated air are totally and fully inactivated.
UVC air sterilizer units that do not have a large enough or properly designed air chamber might simply just let the air pass through and be exposed to the UVC lamp, but not long enough for all the viruses to be inactivated.
But the intensity of the UVC lamp and the time of exposure can still be affected by one other key element of the trinity. And that is…
Proximity
The further we are from a heat source, the less heat we feel. And the closer we are to it, the more heat we receive. It is a similar concept when it comes to UVC sterilization. A UVC lamp might have the proper wattage and wavelength, and it could be running long enough to sterilize the air or a surface, but objects that are too far from it would be sterilized less than those objects that are closer. As well, the sides of the object not facing the UVC light directly (in the shadow) would not be sterilized at all, unless the UVC radiation is reflected.
This is why when it comes to UVC air sterilizers, it’s not just important to expose the air to the proper-intensity UVC lamp for the right amount of time, it’s also important to have the air circulate and be close enough to the UVC lamp in order for it to totally be sterilized before being released back into the room.
Conclusion
Meeting the Functional Trinity’s criteria of UVC sterilization is important in order to ensure that your UVC air sterilizer works properly and as intended. It has to have a strong enough UVC light bulb with the right wavelength, it should be able to hold the air long enough to be treated, and it should move said air close enough to the UVC lamp in order to really sterilize it of the viruses.
Our UltraV Care air sterilizers go above and beyond the Functional Trinity’s criteria for effectiveness. Contact us to learn more or for a free tech demo!