Ventilation Rates and Absences in Offices and Schools

Elementary school classroon, an office and CO2 molecules

Four studies have investigated linkages between ventilation rates and absentee rates in offices and schools; two were performed in offices [29, 30] and two in elementary grade classrooms [21, 31]. The three large studies, one of 40 offices [29], the second of 434 classrooms [21], and the third of 162 classrooms [31] assessed absence over at least full year periods. In the large office study, a 35% decrease in short term absence was associated with a doubling of ventilation rate from 25 to 50 cfm per person, corresponding to a 1.4% decrease in absence per 1 cfm per person increase in ventilation rate. The second office building study [30] found no association of sick leave with building carbon dioxide concentrations as indicators of ventilation rates; however, this study included only two buildings and had experimental periods that did not integrate over the yearly cycle of respiratory disease. In one classroom study [21], on average, for each 100 ppm decrease in the difference between indoor and outdoor CO2 concentrations there was a 1% to 2% relative decrease in the absence rate. Given the relationship of CO2 concentrations with ventilation rates, for each 1 cfm per person increase in ventilation rate, it is estimated that the relative decrease in absence rates is approximately 0.5% to 2%. This relationship applies over an estimated ventilation rate range of 5 to 30 cfm/person, and should not be applied outside those limits. In the second classroom study [31], for each 2.1 cfm per student increase in ventilation rate, on average illness absence decreased by 1.6%. Data relating building ventilation rates and absence rates are very limited. In summary, the limited available data suggest that modest decreases in absence rates could be obtained by increasing building ventilation rates. The expected decreases in absence rates in offices are large enough to be financially significant (see the section of this web site on Impacts of Indoor Environments on Human Performance and Productivity). In some school districts, income from government sources is linked to days of student attendance; thus, increased ventilation rates may increase school district income.