Air Stuffiness and Air Exchange Rate in French Schools and Day-Care Centres

A pilot survey was undertaken from September 2009 to June 2011 in 310 schools and day-care centres distributed in all regions of France including overseas departments. This experimental survey was carried out as part of the preparation of the mandatory control of indoor air quality in public buildings. Three parameters were measured in 896 classrooms or child playrooms: benzene, formaldehyde and carbon dioxide (CO2). The last enables the determination of degree of air ‘stuffiness’ during children occupancy as well as the night-time air change rate. The level of air stuffiness was represented by a score from 0 (no stuffy air) to 5 (extremely stuffy air), which depends on both the occurrence and intensity of CO2 concentration. Moreover, a simple audit of each building was undertaken in order to describe its characteristics, the equipment, user behaviour and outdoor environment. Results show varying levels of air stuffiness from one room to another: low or no air stuffiness was recorded in 30% of rooms, medium to high air stuffiness in 48% of rooms, and very high to extreme air stuffiness in 21% of rooms. The air in day-care centres was generally found to be less stuffy than in schools, because of more favourable ventilation conditions and lower children density per square metre. At the opposite, the air in elementary schools was found to be generally more stuffy than in the other establishments. Air change rates were estimated from the decay of CO2 concentration by an automated method. The observed carbon dioxide values were low at a median level around 0.2 air changes per hour (ac/h) in day-care centres and 0.1 ac/h in nursery or elementary schools. Mechanical ventilation systems were installed in all the day-care centres and used for 60% of the time. They were also installed in the monitored nursery and elementary schools where they were used, on average, for 20% of the time. The most common mechanical systems were based on exhaust ventilation or balanced ventilation directly in the rooms.