Measurement of CO₂ and other values in schools – why we should approach this task during and after the pandemic

 Originally published on January 20, 2021 by Patrick Gebhardt
Last updated on March 03, 2022 • 9 minute read

If you are anything like me, you probably remember the smell of your old school building. As I write these lines, I have the distinct scent of my school's gym mats in my nose, as clearly as if I’m right now facing the terrible task of performing some stupid gymnastic exercise. The same goes for my former classroom: it was somehow musty, stale, steamy. And there was a reason for that: the air was fabulously bad. We know today that an excessively high proportion of CO₂ in the air can have disastrous consequences for concentration and that the levels become critical much earlier than instinctively suspected – depending on how many people are in a room, how old they are, how large their lung capacity is, and other factors. An already degraded air quality starts at 1,000 to about 1,400 ppm CO₂ in indoor air – we know that this value is often exceeded many times over in classrooms, even values of 2,000 up to 5,000 ppm can occur. This poses a risk, in the winter of the SARS-CoV-2 pandemic as well as during normal school operation.

The winter of 2020/21

Why we should keep CO₂ levels down in the classroom air this winter is self-evident. Since we humans exhale CO₂ in every breath (an adult human inhales and exhales approximately 0.5 liters of air with normal respiration), it's an ideal indicator to recognize how “used” air in the classroom already is. And if you have only roughly followed the news situation since January, you couldn't help but learn that aerosol transmission, along with smear and droplet infections, is one of the three transmission paths of SARS-CoV-2. The Federation of European Heating, Ventilation and Air Conditioning Associations (REHVA) recommends in its document Guidance for Schools a threshold value of 800 ppm CO₂ in indoor air before steps have to be taken – a.k.a. the most unpopular child in the class has to quickly open all the windows. Aerosols spread everywhere in a closed room within two to three minutes. This means that in any classroom, one single infected person is enough to infect everyone in that room, with or without a mask, with or without keeping distance. The face mask, as effective as it is in everyday life, can have almost no positive effect in the scenario of a closed schoolroom. Virologists currently can only guess as to how many aerosols contaminated with the novel coronavirus you actually have to inhale to become infected. However, based on influenza viruses, ventilation would have to be provided for several minutes at least after each teaching hour, with windows and doors open. There’s no exact, generalized value, the time frame is defined individually according to the size of the room, the number of school children, their age, activities in the classroom (in music lessons, singing causes significantly higher aerosol emissions), and other factors. But air quality should not only be measured in terms of CO₂ levels, as we know that other factors are also decisive in the pandemic winter: very high temperatures of more than 30 °C inactivate corona viruses, which is why we had a comparatively pronounced drop in case numbers all over the world in the summer months. Sadly, this isn't a real option for heated rooms. Low humidity and very low temperatures, on the other hand, have been shown to allow a long survival time of SARS-CoV-2 on surfaces and in the air. This is also the case at medium temperatures above 20 °C, but only in combination with low humidity. Temperatures above 20 °C, high humidity, and low ppm CO₂ levels would be ideal conditions for school classes in this pandemic winter. Unfortunately, you cannot "feel" those values instinctively and regular ventilation in winter reduces both the indoor temperature and the indoor humidity. This is where CO₂ monitoring comes into play: We don't have to guess, we don't have to go by rule of thumb, we can rely on data that clearly reflect reality. And that means: From 800 ppm CO₂ on, the most unpopular child in the class must quickly open all windows. At least this winter.

Literally all winters

How will this nightmare be finally over? Either SARS-CoV-2 loses its horror, which will probably not happen, or, and this will be the most likely solution, we have managed to vaccinate a substantial part of the population. Can we then go back to the beloved old school practice and cook our children double-sided in rooms with 2,000 to 5,000 ppm CO₂? We should not. More recent studies starting in 2017 show that poor air quality in classrooms (> 2,000 ppm CO₂ average in the classroom) could already reduce the short-term concentration in school children. In addition, it is clearly evident that both the long-term concentration and the precision in examination situations decrease to a significant degree. What we can also keep in mind are other data that we are able to obtain from indoor air, sometimes even with very ordinary, low-cost sensors. Housing materials in sometimes old schools (as well as government offices, public institutions, and other buildings) are no longer state-of-the-art and are potentially harmful to health. Asbestos is only one of the most blatant examples. There are many other substances that are not as feared, but which are also potentially harmful in the long run. The keyword is obviously the assessment of indoor air quality using the sum of volatile organic compounds (TVOC value). Sensors can be able to reveal the TVOC value and provide good arguments for investing in the future of buildings, using healthy building materials. These are materials that do not contain pollutants capable of triggering diseases or allergies through evaporation. An investment made in CO₂-measurement during the current pandemic winter is therefore not "money lost," but a wise investment in the long term.

Montessori school Herzogenaurach

Since at least 2017, Paessler has been working selectively on solutions for the Internet of Things (IoT), a network of communicating devices and sensors. This work is cumulating into scalable solutions for various fields of application, which we have either already presented or will soon. In a nutshell, we can say: evaluated data make the reality around us visible – we map this knowledge in our solutions; clearly arranged, always in a way that allows you to work with it. The monitoring of CO₂ is part of our solution for building status monitoring, which we have already put into practice. We believe that in the current pandemic, the technological sector is needed to develop at least partial solutions. Our founder Dirk Paessler felt committed to this idealistic goal already in spring, when he launched CovidCare, an online tool to better estimate the utilization of hospitals with SARS-CoV-2 patients, both in normal wards and in the intensive care unit. We hope to be able to also make a positive impact during the second pandemic wave, which is hitting Europe right now. We've recently implemented the measurements of CO₂ and other values at the Montessori school Herzogenaurach, which can be seen as pilot project for identical or similar implementations in other educational institutions.