Carbon Dioxide Levels and Ventilation Rates in Schools

In the following, measurements of CO2 levels in seven classrooms in four schools are reported. Measurements were taken for approximately one week in each classroom during the heating season and the time-varying ventilation rates estimated. The results of the experiments show CO2 concentrations which are far beyond the guideline value of 1000 ppm (the average concentration during the occupied period was 1957 ppm). In some classrooms the level exceeded the range of the detector (4000ppm). Calculated air supply rates vary from unacceptably low levels to rates which are in line with guidance (the average occupied rate was 0.84 ac/h or 1.38 l/s.p). The occurrence of periods with acceptable supply rates, and the rates found during purge ventilation, show that the surveyed classrooms have the potential to provide adequate fresh air. Anecdotal evidence from the classroom teachers suggest that the reason enough fresh air is not being provided is the reluctance of staff to open windows: firstly because of the draughts this might cause, and secondly, because they are unaware of a problem.