Ventilation Rates and Sick Building Syndrome Symptoms
Many studies have investigated the linkage between ventilation rates and the proportion of the occupants reporting sick building syndrome (SBS) symptoms. Most studies have collected symptom and ventilation rate data from sets of five to 160 buildings or building spaces and assessed how symptom reporting rates were correlated with ventilation rates, using statistical models to control for other factors. A few studies experimentally manipulated ventilation rates in one or a few buildings and assessed how symptom reporting rates or symptom severity varied with changes in ventilation rate. Occupants were unaware of the ventilation rates during the various experimental periods. Considering the full set of studies, ventilation rates spanned a very broad range from zero mechanical ventilation and an uncharacterized amount of infiltration to total ventilation of more than 100 cfm per person. In many individual studies, building ventilation rates spanned a smaller range from approximately 10 to 35 cfm per person.
Two critical reviews of this literature have been performed. In the review by Seppänen et al. [21], 20 out of 27 studies found a statistically significant increase in reporting of at least one SBS symptom among occupants of the study buildings with lower ventilation rates. In nine of these studies, there was at least an 80% increase in the fraction of occupants reporting at least one of the types of SBS symptoms in the buildings with lower ventilation rates. The second critical review [28] was performed by an interdisciplinary group from Europe and concluded that "increasing the ventilation rate .....decreases the prevalence rates of SBS symptoms" This interdisciplinary group also concluded that "ventilation rates below 25 liters per second per person [50 cfm per person] in offices can increase the risk of health and comfort problems".
The largest U.S. study of building characteristics and occupant symptoms is the EPA Building Assessment Survey and Evaluation (BASE) Study of 100 representative office buildings. Analyses of data from this study [29] indicate a general decrease in SBS symptoms as study space ventilation rates increase from as low as 10 cfm per person up to approximately 25 to 35 cfm per person, while current U.S. building codes and professional standards generally require a minimum of 15 to 20 cfm per person in offices. Twenty percent to 30% fewer occupants reported SBS symptoms in study spaces with ventilation rates above 20 to 25 cfm per person, compared to study spaces with lower rates typically ranging between 10 and 20 cfm per person.
Many of the studies of how ventilation rate affects SBS symptoms have measured indoor CO2 concentrations. In the majority of these studies, a larger fraction of occupants reported SBS symptoms in buildings with higher CO2 concentrations [21].