Belgian legislation on indoor air quality

Back to School – CO2 and Class Breakdown

With the return to school in September 2021, concerns appear among parents. The return of children to class (in a closed space), when most of them have not yet been vaccinated and the Delta variant is much more contagious than the original COVID19, is a legitimate source of concern.

We did a little study of the keywords related to CO2 sensors, and it is clear that it is back to school (and therefore the measurement of CO2 at school) that is the main topic of discussions on the networks. social (Twitter, Facebook).


Our governments are pushing for the use of CO2 sensors to control the CO2 concentration in confined spaces, because CO2 is a faithful image of air pollution, and therefore of the lack of ventilation. The objective is obviously to ensure that all premises are well ventilated.

CO2 concentrations at school

Belgian regulations impose a CO2 rate of 900ppm (or 500ppm above the external CO2 rate). Out of studies have shown that without ventilation and without aeration, the CO2 concentration rose after half an hour to 1500ppm in a class.

A study published in autumn 2017 by Bruxelles Environnement (written by Catherine Massart, Architect and Climate UCL) mentions that “In Belgium, very many schools do not have mechanical ventilation”. Without mechanical ventilation, it is therefore necessary to ventilate (= open the windows) very regularly.

In this same study, which can be found here, we discover CO2 concentrations measured in course classes. We are very, but really very far, from authorized legal values!


A school in Louvain-La-Neuve, after renovation of the frames (waterproofing)


It is therefore more than urgent, for schools, to ensure that the classrooms are ventilated very regularly. And control the pollutant concentration by installing CO2 sensors. And this in order to prevent COVID19 contamination.