Carbon dioxide (CO2) in indoor air

Carbon dioxide (CO₂), which exists naturally in the atmosphere, is a molecule produced by the human body through breathing. Its concentration in indoor air in buildings depends on human occupancy and air exchange rates, and is an indicator of air quality in closed spaces.

This is why the concentration of CO₂ in indoor air is a criterion on which regulations for building ventilation are based. The current regulatory and normative limit values usually vary from 1000 to 1500 ppm. They are applicable to school premises as well as buildings for housing and office use and have no significance in terms of the health quality of indoor air. 

The Agency's work

In support of the updating by public authorities of the regulations on building ventilation, the Agency published today an expert appraisal which provides a status report on the concentration levels of CO₂ in indoor air and its links to effects on health. 

Based on an analysis of the scientific literature and one of the levels of CO₂ and other air pollutants detected in France in housing, schools, daycare centres and offices, several conclusions and recommendation have been issued by ANSES.

• the Agency declares that CO₂ can be used as an indicator of air quality in closed spaces and recommends basing strategies for sampling CO2 in indoor environments on the French NF EN ISO 16000-26 standard;
• the Agency recommends that indoor air quality guideline values (IAGVs) for CO₂ not be set, neither for its intrinsic effects nor for "closed space" effects on health. It emphasises the fact that CO2 measurements cannot be considered as the only indicator of indoor air health quality due to results of studies which show that:
  • the available epidemiological data do not enable setting a threshold value for CO₂ that would protect individuals from the effects of closed spaces on health, on perceived comfort and on cognitive performance; 
  • in the air of housing, schools and offices in France, the probability of surpassing the health target values for various chemical pollutants (formaldehyde IAGV, etc.) is not inexistent even at low levels of CO₂.

As regards the intrinsic effects of CO₂, a recent experimental study on humans suggests that CO₂ may affect psychomotor performance (decision making, problem resolution) starting at 1000 ppm. Since there are no other studies which concur with these findings and no consensus on the related mode of action, the Agency recommends improving knowledge on these suspected effects. 

The available data found higher levels of CO₂ in the air of school rooms than in the other indoor environments studied (housing, offices, day care centres), and certain studies emphasised a link between these levels and effects on pupils’ health (asthma-like symptoms), cognitive performance and their perception of comfort.

The Agency therefore wishes to emphasise the importance of heightening the awareness of municipal technical services, school directors and teachers about the measures that can help to effectively reduce the effects of closed spaces on health, performance and perceived comfort, including ventilation through opening windows and doors. The ventilation strategy must take into account certain elements such as noise pollution, the transfer of outdoor air pollution, thermal comfort, etc. 

This  ventilation strategy must be used in addition to controlling sources of pollution, especially the choice of building, decoration and furnishing materials, cleaning products, school supplies, etc. 

Finally, ANSES recommends assessing the relevance of revising the occupational exposure limit (OEL) for CO₂, and in particular the relevance of setting a short-term OEL.