Why regularly ventilating indoor spaces to control Covid-19?

Air quality has emerged as a factor to be considered in health crisis management and it is generally accepted that the risk of COVID-19 contamination can be reduced by effective ventilation. This is due to the fact that ventilation reduces the number of airborne microdroplets emitted by potentially contaminated and contagious occupants in the building.

Read more about the benefits of ventilation in the prevention of Covid-19 

How to measure air quality?

It is difficult to measure the presence of the virus in the air. In order to characterise the air quality, it is easier to measure the presence of CO2 which is emitted by the occupants and may indicate insufficient ventilation of the indoor spaces. The further the CO2 level is from the outdoor level (± 400 ppm), the worse the air quality is.
What are the CO2 standards in higher education?

Outdoor air contains approximately 400 ppm CO2, but this reference level can be higher when the external air quality is poor (urban environment, weather conditions, etc.).

The ideal standard is an indoor air CO2 concentration below 900 ppm. Taking into account the quality of the outdoor air which influences the CO2 level, the acceptable threshold for air quality is between 900 ppm and 1200 ppm. These standards are defined in Circular 8364 of the Wallonia-Brussels Federation (29/11/2021).

Air quality monitoring network

ULiège has set up an air quality monitoring network consisting of about a hundred CO2 sensors distributed throughout the institution's various infrastructures. The data recorded allow an assessment of the air quality and the taking of the necessary measures at the level of the Institution. The data measured by the monitoring network is regularly included in the SARS-COV-2 dashboard of the ULiège.

In addition to the CO2 sensors integrated into the monitoring network, ULiège has also equipped itself with additional sensors informing the occupants of the rooms of the CO2 level in real time and warning them that ventilation is necessary. This alarm can be light and/or sound depending on the sensor model. During the academic year 2021-2022, CO2 sensors were placed in all classrooms with more than 30 seats on the Sart-Tilman and Liège centre campuses, and with more than 50 seats on the Arlon and Gembloux campuses. In the academic year 2022-2023, all classrooms with at least 30 seats will be equipped with sensors.  

Recommendations for room ventilation

- Mechanically ventilated rooms

Some rooms are equipped with a mechanical ventilation system with supply and exhaust units. This is often the case for large lecture theatres and laboratories, as well as for some meeting rooms and open plan offices.

The mechanical ventilation operates throughout the day, without interruption, with fresh air. For classrooms and lecture theatres with a booking system on CELCAT, the ventilation is switched on during booking periods and continues for some time after the last lecture. These arrangements allow for regular air renewal and do not require any intervention from the occupants.

- Non-mechanically ventilated rooms

All rooms without mechanical ventilation should be ventilated by the occupants.

In order of effectiveness, the following ventilation measures are recommended

  1. open windows for the duration of the occupancy of the room;
  2. ventilate a few minutes at regular intervals (e.g. every 15 to 20 minutes);
  3. ventilate for about 15 minutes every hour.

It is particularly recommended that the ventilation of classrooms be systematised by opening doors and windows for 15 minutes before and after each occupation, as well as during breaks, even if the air quality thresholds are acceptable.

Portable sensors are available for loan, especially for open-plan offices, meeting rooms and refectories (see below).

How do you report exceeding the 1200 ppm threshold in a room?

You should only report exceeding the 1200 ppm threshold in a room if measures have been taken to ventilate the room (e.g. opening of windows) and these measures have not resulted in a decrease below the threshold.

Alerts should be entered via the online form (link below). The reports will be forwarded to the relevant departments for analysis and possible adaptation of preventive measures.

Form for reporting exceeding the 1200 ppm threshold

CO2 sensors used at ULiège

ULiège is equipped with several types of CO2 sensors. Some of them feed the monitoring network and others inform the occupants of the rooms about the air quality in real time, allowing them to take immediate action.

- Sensors integrated into the monitoring network

The CO2 sensors integrated into the monitoring network are distributed throughout the various ULiège infrastructures.

Some of these sensors are also equipped with indicator lights allowing the occupants of the premises to take the necessary measures and to check the effectiveness of these measures in real time. An information sheet is available near these sensors.


Learn more about sensors with indicator lights 

- Sensors with visual and audible alarms

Sensors with visual and audible alarms are designed to warn occupants in real time when ventilation of the premises is necessary.


Learn more about sensors with visual and audible alarms

- Portable sensors

The Service Universitaire de Protection et d'Hygiène du Travail (SUPHT) makes a portable CO2 detector available to users who so wish (for shared offices, common rooms, etc.).

A detector can be lent via the SUPHT SHOP, building B12a, Clos Mercator, 12 au Sart-Tilman on Tuesday and Thursday mornings between 9am and 12pm.

20220119 180412 (002) 

More information on portable detectors

More information for their loan 

Service Universitaire de Protection et d'Hygiène du Travail (SUPHT)

+32 (0) 4 366 22 47


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