Germicidal effect and inactivation:
Traditional UVC works by penetrating the cells and destroying the hydrogen bonds in DNA and RNA. It has been found that this happens most optimally at a wavelength of around 260 nm. However, this may vary slightly depending on the different pathogens – so a natural light scattering between 240 and 280 nm may be beneficial.
This means that, depending on the individual pathogen structure of RNA and DNA, very different amounts of energy are required to destroy these bonds. Therefore, it is important to know the exact dose needed to destroy the pathogen you want to inactivate. This varies individually, also between the different groups.
There are bacteria that can easily be inactivated with a low dose, for example 20 J/m2, but there are also bacteria that require more than 500 J/m2. The same applies to viruses where the differences can be very large. When it comes to yeast and mould, a dose of up to 10,000 J/m2 may be required.
When working with inactivation of bacteria and viruses, you always look at how large a part of a given colony you can inactivate. This is typically described as the disinfection effect. It is most often calculated as a percentage: 90%, 99%, 99.9% and up to 99.999%. However, the one common factor is that it is impossible to achieve 100% – regardless of whether you use chemicals or UVC light. A part of the population will always survive.
Standard figures for the use of UVC are typically calculated at a rate of 90%. The reported dose is the one that achieves a 90% reduction of a population. Typically, if you want to go from 90 to 99%, it requires twice the amount of energy, and the same applies to an increase from 99% to 99.9%. However, you should always examine it specifically for the pathogen you want to reduce, as fluctuations may also occur in this regard.
If you come across products that promise 100% or 99.999% effect/inactivation rate of all pathogens, you should naturally be sceptical. This will require an extremely large amount of energy; as mentioned, there are pathogens that require over 10,000 J/m2 to achieve a 90% reduction.
At the same time, there is a big difference in how the laboratory tests the effect on a pathogen in a clinical solution of clear water – in comparison to how the energy can reach the pathogen in an actual situation in a factory or an office.
This is where your supplier’s experience and qualifications come in
We are always happy to come visit for a non-committal talk and for a control measurement of your UVC system.