Ventilation Rates and Absences in Offices and Schools
Three studies have investigated linkages between ventilation rates and absentee rates; two were performed in offices [26, 27] and one in elementary grade classrooms [19]. The two large studies, one of 40 offices [26] and the second of 434 classrooms [19], assessed absence over 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 [27] 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 the classroom study, on average, absence rates decreased by 1% to 2% for each 100 ppm decrease in the difference between indoor and outdoor CO2 concentration. Given the relationship of CO2 concentrations with ventilation rates, it is estimated that absence rates decreased 0.4% to 0.9% for each 1 cfm per person increase in ventilation rate. 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.