Ventilation Rates and Absences in Offices and Schools

Eight studies were identified that investigated linkages between ventilation rates and absence rates. Three studies were performed in offices [28-30], four studies were performed in elementary grade classrooms [31-34], and one study assessed ventilation and absence in day care centers [35]. Most of these studies tracked absence over a period of a full year or more [28, 29, 31-34] although only one of these studies [32] also monitored ventilation rates over the full time period. 

Among the three studies in offices, only one [28] found a statistically significant increase in absence with lower ventilation rates. In this study, a 35% decrease in short term absence was associated with a doubling of ventilation rate from 25 to 50 cfm (12 to 24 L/s) per person, corresponding to a 1.4% decrease in absence per 1 cfm (0.47 L/s) per person increase in ventilation rate. The two other studies in offices had high ventilation rates which might explain the lack of associations. In one study [30], weekly mean worktime CO2 concentrations were only 37 to 250 ppm above outdoor air CO2 concentrations indicating very high ventilation rates. For reference, some ventilation standards recommend ventilation rates that maintain indoor CO2 concentrations no more than about 700 ppm above the outdoor air CO2 concentration. The second study reported very high ventilation rates, mostly between 34 and 90 cfm per occupant (16 and 42 L/s per occupant).

Among the five studies from schools or daycare buildings, four found statistically significant decreases in absence rates with more ventilation or lower carbon dioxide concentrations. The strongest study, which followed 162 classrooms for two years [32], found a 1.6% decrease in absence for each 2 cfm (1 L/s) per person increase in ventilation rate. Because ventilation rates in most classrooms can be increased by at least several cfm (a few L/s) per person, the study indicates a potential to reduce absence by several percent. A second classroom study [31], reported a 1% to 2% relative decrease in the absence rate for each 100 ppm decrease in the difference between indoor and outdoor CO2 concentrations. A third classroom study [33] reported that absence increased by 0.4 days per year for each 100 ppm increase in time average indoor CO2 concentration, while the fourth classroom study [34] found no statistically significant association of ventilation rates with absence. In the study of day care centers [35] there was a statistically significant 12% decrease in sick leave per each 1 h-1 increase in air exchange rate. There was also a 2% increase in sick leave per each 100 ppm increase in indoor CO2 concentration, but the association was not statistically significant. Overall, the available research indicates that increased ventilation rates in classrooms are associated with reduced student absence. For elementary and middle school students, reduced student absence has been shown to be associated with higher grade point averages and higher scores in academic achievement tests [36].

In offices, even very small decreases in absence rates from increases in ventilation rates would be financially significant (see the section of this web site on Human Performance). In some school districts, income from government sources is linked to days of student attendance; thus, increased ventilation rates may increase school district income.