The Omicron mutation of Sars-Cov-2 is the star of the moment. Highly transmissible, fortunately of lesser severity, at least for those who are immunized. And what’s the next one going to be? Between the original strain and the omicron, it took two years. What have we learned in this period, and what has actually been done to improve people’s safety indoors?
The omicron made it clear once again that the preferred route of contamination is aerial transmission, where aerosols emitted by a contaminated person can remain floating in the air for hours, accumulating in a closed environment and inspired by healthy people in that space. Aerosols emitted by people are microscopic droplets of mucus that can contain pathogens, emitted when speaking and even exhale. It is not necessary to cough or sneeze. Just breathe. The aerosol receiver has no defense: depending on the load, it will be contaminated. If his immune condition is good, lucky for him, the progression of the disease will not be severe, fortunately.
So, do I have to stay in a room for hours to get contaminated? No: there at the beginning of Covid there were already reports of contaminated people in restaurants, in musical auditions and other events, where they remained for a short time, or even very distant from the contaminant, that is, the sick person at the time. Some of these reports were confirmed by technical studies, consolidating the knowledge of the mechanism of airborne transmission. Just you be in the vicinity of an emitter, the dispersion of aerosols, so small that they behave like gas molecules in the air, will make them reach you. Imagine yourself in a restaurant, or bar, without a mask!
We also learn that masks help, but to be effective, they need to have a good standard. What’s the point of a mask that retains only 50% of the aerosols that come to you? Better to use one that retains 95% as the N95. Otherwise, we’re only half protected…
We also learned that the probability of airborne virus transmission is lower in open environments. But it always depends on the proximity of the people around you, as well as the wind direction…
Much has been said and recommended in order to improve air conditioning systems, since they are present in many closed spaces, a cause of concern. Better turn off the air conditioning and open the windows? Perhaps, but nothing is guaranteed. Our constructions are not made to ensure good ventilation and we will always depend on the wind. On the other hand, most air conditioning systems do not even have air renewal and, when they have, even if sized according to the best standards, maximum air renewals are around 3 air changes per hour. This equates to a change at every 20 minutes. And the exchange is not like that, all at once. All of a sudden, clean air? No! Air renewal is continuous, maximum usually at 10 % of the total flow. It’s like wanting to clean a dirty pool with the flow of clean water from a small hose…
Taxi and app vehicles, all right, the window area is great with respect to volume. Windows open, of course! Now, when it stops at the traffic light, no air movement, it’s a critical situation. What about public transportation? It’s complicated: Metros and many buses don’t even have windows that open! And when they open, they’ve minimal apertures.
Better to close everything and trust the air conditioning system? No. The way existing systems are, absolutely not. To hold aerosols, only filters with high efficiency in the range of 5 microns. Only operating room systems in good hospitals and certain areas of industrial production use filters like this. Airplanes are a good example. In them the air is recirculated in a smaller proportion and yet all processed air passes through high efficiency filters. Modifying existing systems to support filters of this type is most often unfeasible.
Time to ask if there are solutions available, and how they rate. Increase air renewal, increase the degree of filtration, use air purifiers with ultraviolet light, bipolar ionizers, portable purifiers with HEPA filters, decrease the overall concentration of contaminants, reducing the likelihood of contamination. They do not solve, however, the possible direct contamination, between you and me, for example, talking in an office or in a bar, whatever. The only effective existing solutions for this, which act in the space between the contaminant and the possible contaminated, are the control of air movement and air purifiers based on photocatalysis.
Controlled airflow, such as in airplanes, which have general flow from top to bottom, or in underfloor air conditioning diffusion systems, with bottom-up flow, drag contaminants away from the receiver, reducing the concentration of contaminants around the emitter. Aircraft, however restricted, have surprisingly low infection rates, as well as the benefits in terms of air quality in buildings with floor air diffusion systems are well known.
Photocatalytic air purifiers generate hydrogen peroxide, a highly reactive gas, which effectively eliminates single-cell microorganisms. Hydrogen peroxide is, however, friendly to multicellular beings. The introduction of hydrogen peroxide inside a room, replicates a process that occurs in nature every day. The sun, when reaching certain metal oxides in the soil, recombines water vapor and oxygen molecules present in the air, transforming them into hydrogen peroxide. The more peroxide present, the cleaner the air, freer of microorganisms and organic gases, ozone or nitrogen oxides, typical urban pollutants.
In a nutshell, photocatalysis is an active air purification process. The peroxide molecules disperse through a closed room, coming into contact with the aerosols that contain the viruses, disabling them. It is a proven efficient process against Covid-19 virus and many other viruses and bacteria. Used in all types of applications, in thousands of locations around the world, including spacecrafts, photocatalytic air purifiers are supplied by many manufacturers around the world. It is an available solution, although strangely little publicized and more so, recommended only by a few official bodies and professional entities.
But that kind of behavior is well known, isn’t it? Viruses aren’t comets, but they’re a problem. And the problem is in the air! You don’t see them, unfortunately, but they are there. Of course, we recognize that all biological contaminant control technologies should be used whenever possible and undoubtedly have an additive effect. The result of the application of different technologies in the same place thus results in a summation. However, for all that has been put, it stands clear that the use of an active purification technology is mandatory. Be controlled air movement, or active air purification by photocatalysis!
Ricardo Cherem de Abreu
Mechanical Engineer and MSc by UFSC
Technical Director at Dannenge International
