Associations between Indoor CO₂ Concentrations and Sick Building Syndrome Symptoms in US Office Buildings: An Analysis of the 1994-1996 BASE Study Data

Higher indoor concentrations of air pollutants due, in part, to lower ventilation rates are a potential cause of sick building syndrome (SBS) symptoms in office workers. The indoor carbon dioxide (CO₂) concentration is an approximate surrogate for indoor concentrations of other occupant-generated pollutants and for ventilation rate per occupant. Using multivariate logistic regression (MLR) analyses, we evaluated the relationship between indoor CO₂ concentrations and SBS symptoms in occupants from a probability sample of 41 U.S. office buildings. Two CO₂ metrics were constructed: average workday indoor minus average outdoor CO₂ (dCO₂, range 6-418 ppm), and maximum indoor one-hour moving average CO₂ minus outdoor CO₂ concentrations (dCO₂MAX). MLR analyses quantified dCO₂/SBS symptom associations, adjusting for personal and environmental factors. A dose-response relationship (p<0.05) with odds ratios per 100 ppm dCO₂ ranging from 1.2 to 1.5 for sore throat, nose/sinus, tight chest, and wheezing was observed. The dCO₂MAX/SBS regression results were similar. Implications: large increases in ventilation rate or improvements in ventilation effectiveness and/or indoor pollutant source control would be expected to decrease the prevalence of selected symptoms by up to 70-85%.