Additional levers
Outdoor air, adapted filtration and reduction of emission or occupancy.
02Inland air
Indoor Ventilation: Improving Air Quality
In an occupied space, air renewal dilutes pollutants emitted indoors, including respiratory particles. Ventilation complements other preventive measures; it cannot by itself establish that a place is risk-free.
AnswerThe essential first
In practice
The short answer
Start by checking that air inputs and outlets are not obstructed. When conditions permit, open several openings to create a renewal air, reduce density and occupancy time, and maintain mechanical systems as directed. A CO2 sensor helps to detect an accumulation related to occupation, but it does not detect viruses.
indicator, no virus detector
It mainly provides information on the accumulation of expired air in occupied space.
system maintenance
Filters, mouths and settings must follow the manufacturer's and building's instructions.
01Understanding the situation
When to strengthen air renewal
The need increases with the number of people, duration, vocal or physical effort, the volume of the room and the presence of symptomatic or vulnerable people.
Prior to occupation
Return the system to operation and prepare the ventilation before a meeting, course or extended reception.
During a heavy occupation
Strengthen the intake of outdoor air and avoid blocking the mouths with furniture or objects.
After dense activity
Continue the air renewal after a meeting, physical exercise or prolonged occupation.
In the presence of symptoms
Cleaner air mix, reduced contact, respiratory hygiene and applicable health recommendations.
During work or outdoor pollution
Adapt the strategy: Open can be counterproductive in case of smoke, heavy pollution or external contaminant.
02Step by step
Diagnosing before buying a device
A lasting improvement begins with the existing building. A mobile device does not correct a ventilation failure or a poor air distribution.
Identify openings and mouths
Locate windows, input grids, extraction and blowing, without changing the technical settings at random.
Observe occupation
Note how many people use the premises, how long and for what activity.
Test a safe ventilation
When outdoor air is compatible, open in such a way as to promote renewal without creating a danger of extreme fall or discomfort.
Check the mechanical system
Check hours, maintenance, filters and absence of obstruction with the responsible person.
Interpret CO2 in context
Follow the trend during occupation rather than a single measurement; place the sensor according to its instructions, away from a face or window.
Document and adjust
Compare situations, record actions and ask for expertise if the problem persists.
03Decision points
Choose a proportionate action
The context determines the right measure. Use these markers to choose the next action and when to ask for help.
Natural ventilation
Immediate solution if weather, outdoor pollution, safety of openings and comfort allow.
Mechanical ventilation
It must function according to the design of the building. Any major change is the responsibility of a competent professional.
Mobile filtration
A properly sized HEPA device can complete the ventilation; check the useful flow, noise, location and maintenance.
Comparer deux purificateurs
Pour la pièce réellement utilisée, comparez le débit d’air propre (CADR) adapté aux particules fines, la surface annoncée, le bruit à la vitesse prévue et le coût des filtres. Écartez les appareils qui produisent intentionnellement de l’ozone. Un filtre ne traite ni une source d’humidité ni une panne de ventilation.
Arbitrer entre fenêtre et filtration
Si l’air extérieur est chargé de fumée ou de pollution, évitez de traiter l’ouverture des fenêtres comme une règle automatique : suivez l’alerte locale, limitez les sources de particules intérieures et faites vérifier le fonctionnement de la ventilation du bâtiment. Revenez à l’aération habituelle lorsque les conditions extérieures le permettent.
In practiceObserve and understand
Air renewal and filtration: two different approaches
Airflow must be considered relative to room volume. Ventilation brings in outdoor air; filtration removes particles from the air passing through a filter. They complement each other, but HEPA filtration does not remove CO₂.
| Approach | What it provides | What to check |
|---|---|---|
| Outdoor air | Dilution of indoor pollutants. | Openings, ventilation, safety and outdoor air quality. |
| HEPA filtration | Removal of particles from the treated airflow. | Rated clean air delivery, operating setting, maintenance and placement. |
| Organization | Less time or fewer people in the same space. | Possibility of moving an activity outdoors or limiting occupancy. |
Keep in mind
The calculation illustrates only airflow divided by volume. It measures neither actual fresh air, CO₂ nor infection probability; building design requires a technical assessment.
References for these explanations
04Not to be done
Frequent errors
- Interpret a CO2 figure as a direct measure of infectious risk.
- Condemning an air intake because it causes a sensation of air current.
- Buy a non-dimensional purifier for the volume and occupancy of the premises.
- Create a powerful airflow directly from one person to another.
- Open without regard to external pollution, smoke or a risk of falling.
Important limitVentilation of a building is a subject of safety and engineering. Do not alter a collective system, extraction or safety device without authorization. In the event of persistent doubt, mould, unusual smell or repeated symptoms, have the room evaluated by the appropriate interlocutors.
Frequently Asked Questions
Does CO2 measure the presence of viruses?
No. A CO2 sensor does not detect viruses or bacteria. In an occupied location, the CO2 trend can help to assess the exhaled air accumulation and the efficiency of renewal, but it must be interpreted with the occupancy and configuration of the space.
Is opening a window enough for a few minutes?
The effect depends on the volume, number and position of the openings, wind, temperature difference and occupancy. Opposite openings often encourage faster renewal when they can be used safely.
Does a purifier replace ventilation?
No. A suitable HEPA filter can reduce some particles in suspension, but it does not replace the minimum intake of outdoor air, does not correct a failed extraction and does not eliminate all contaminants.
Le CO2 baisse après la mise en marche d’un purificateur : est-ce une preuve que l’air est plus sûr ?
Non. Le CO2 renseigne surtout sur l’air expiré et le renouvellement par l’air extérieur. Un purificateur peut retirer des particules sans faire baisser le CO2. Inversement, un CO2 plus bas ne prouve pas l’absence d’agent infectieux. Évaluez séparément l’occupation, la ventilation, le débit de filtration et les autres mesures de prévention.
Do you need to change the settings of the VMC or heating itself?
Not if you don't know the system. The settings, filters and flow balances can affect several locations. Consult the package leaflet, the manager or a competent professional.
Check implementation
These points serve as a reminder to prepare the action. The boxes are not registered.
Sources used
These institutional references provide a means of checking the guide and accessing the full recommendations.
PratiqueCheck before deciding
Votre liste de vérification
- Locate air inlets and outlets and keep them unobstructed.
- Vérifier l’entretien de la ventilation mécanique.
- Consider the number of occupants and the time spent in the room.
- Read a CO2 measurement as an indicator of air renewal, not as an infection test.
Use alongside the guide’s steps, limitations and sources.
Folder Illustrations
Images generated by artificial intelligence to put the subject in context.
Image generated by artificial intelligence. Fictional AI-generated scene, not medical evidence or a diagnosis.