Air sterilizers & cleaners, how to choose and what to avoid?
Many of you contact us with questions on how to navigate yourself within air sterilizers (in the presence of people). I therefore decided to write this short blog where I will try to answer all your questions.
- Search for devices according to their characteristics - what a device can physically do; avoid beautiful but misleading images
- Do not use devices that emit blue light!!!
- When it comes to germicidal air cleaners, saving money does not mean buying cheap
- Disinfection itself it not enough, you also need to clean (filter)
Usually people get an air sterilizer when they need to protect themselves and reduce the risk of transmission of for example COVID-19; but also the flu or a bacterial infection. The purpose of this device is therefore to eliminate these microorganisms found in the air.
A variety of sterilizers, also called germicidal emitters or cleaners, are available on the market. I am talking, of course, about sealed radiators that allow air to be disinfected in the presence of people. For this purpose the technology of UV-C light (or also called UV-C radiation) is used. UV-C has the ability to "break down" the virus's DNA, preventing it from multiplying and eventually dying. If you are interested in learning more about this topic, check out my other blog on a similar topic https://athmoss.sk/blog/how-to-disinfect-and-clean-the-air or watch videos such as https://www.youtube.com/watch?v=D23_6EytyF4. There are countless scientific studies on the subject.
A key feature of any well designed and built sealed emitter is the fact that it must not emit any UV-C light outside of its structure. However, as with all products and goods, also in the case of germicidal radiators you can find variety of everything. There are really high-quality devices on the market which are equipped with UV-C disinfection chambers with complete separation from the environment. And, of course, there are also such "great" ones, from which you can see blue light emitting during its operation. I even came across a manufacturer that told me it was "reflected UV-C which was not dangerous". Unfortunately, this is not true. If you see a blue light, do not use such a device, as your eyes, skin and body are exposed to UV-C radiation. This radiation decomposes any organic material, in a certain dose, your skin, retina, etc. Avoid such devices and if you have it under warranty, I recommend that you contact your dealer for a refund.
UV-C reflectance table (253,7nm) for selected materials.
Stainless Steel (various classes) 20-28%
Metal (based on finish) 50-60%
White Office Paper 25%
Scientific studies have shown that UV-C disinfection alone is not enough for closed types of sterilizers.  It is also necessary to clean the air, in other words, mechanically filter. "Pathogenic microorganisms enter the air mainly in two ways: settled on dust particles and dispersed in small droplets, which fly out of mouths of infected people during sneezing, coughing, etc."  Viruses thus travel on significantly larger particles than themselves. For example, SARS-CoV-2 virus (the causative agent of COVID-19) is approximately 120 nm in size (0.12 μm). It can move on particles (droplets) with a size of about 2-5µm and more. Today, very efficient HEPA filters can filter out 95 ~ 99% of particles larger than 0.3 µm and thus effectively prevent the spread of viruses. Any particles "trapped" in sealed germicidal emitters with a HEPA filter are then exposed to a large dose of UV-C, which reliably kills them. The HEPA filter itself has only the ability of mechanical "capture", it cannot kill microorganisms. Therefore, it is necessary to combine these 2 technologies (UV-C and HEPA).
Here I want to point out that you should be altered by so-called sealed germicidal radiators without any filtration. Virus killing is a function of UV-C dose in mJ / cm2, otherwise called a dose. Thus the dose of UV-C and time (similar when cooking, heat and time). If you do not have a filter, there´s nothing inside to mechanically catch the virus and the air around the tubes can flow so fast that the necessary dose to inactivate the virus is not reached. The UV-C performance in this case can be tremendous, but it's like wanting to cook meat in 1 minute, but instead of 90°C water, you would want to use 200°C water. You simply won't cook it because your water will evaporate. In short, you need more time. Therefore, read the technical brochures of the machines carefully whether they contain a HEPA filter.
Those high-end machines also contain a so-called pre-filter. This removes large particles such as dust, hair, microscopic pieces of skin, etc. from the filtered air. Such organic substances can decompose under the influence of UV-C to sulfur compounds that leads also to considerable odor. Therefore a prefilter is definitely a good choice.
Air purifiers tend to also have a carbon filter, which are basically carbon balls in some form (e.g., plastic package with mesh). This filter is important if you would like to absorb, for example: cigarette smoke. Odor perception is quite an individual matter; from my experience we have not come to some great results by applying different types of carbon filters with different thicknesses (performances). Maybe that's because we design the equipment primarily for air disinfection in non-smoking areas and areas where there are no animals (retirement homes, city offices, school lobbies, banks, waiting rooms or production halls).
Last but not least, installation flexibility is very important. There are devices that can only be placed on the wall. There are those that are only mobile. And then there are the ones that are flexible. In our experience, for example, retirement homes cannot have devices on mobile stands due to movement of immobile patients. Wall mounting is key here. At school, a mobile stand is needed to move between the rooms. Therefore, it is smart to choose a device that has several possible installations. This way you will be flexible when installing even after a longer period of use.
Finally, a frequently asked question: Is a closed germicidal emitter a general cure and will it prevent the transmission of a virus or bacteria? I will answer that it is not a general cure. These devices suck in the surrounding air, disinfect it and return it cleaned to the room (if the device is equipped with the necessary filtration), this will reliably prevent the spread if the distance between the infectious person and the potential carriers is sufficient. The device will certainly not protect you if you sit next to an infectious person without a mask who sneezes at you. The best combination is - disinfected hands, face mask and continuous air cleaning and disinfecting. With suitable placement of a closed germicidal radiator, you will achieve proper air circulation and thus suction of exhaled droplets from people and their direct decontamination. This way you can really minimize the possible transmission of diseases. In addition, active filtration (HEPA) can minimize particles that act as "vehicles" for viruses and bacteria.
I believe this blog is beneficial for you. In case you have any questions, I am at your disposal at the email address firstname.lastname@example.org.
Ing. Peter Hrubina
Head of Export department
 Ultra-Violet Reflecting Power of Aluminum and Several Other Metals; W.W. Coblentz and R. Stair.
Using UV Reflective Materials to Maximize
Disinfection, Application Note AN011, 16.06.2016, Crystal IS.
 (Setti et all); Talianska spoločnosť pre environmentálnu medicínu (SIMA).
 Dezinfekcia vzduchu, Miroslav Zikmund, str. 202.