Outdoor Air Ventilation and Work-Related Symptoms in U.S. Office Buildings - Results from the Base Study
Background: Recommendations for outdoor air ventilation rates in office buildings balance the need to dilute indoor pollutants for both health and comfort of the occupants against the costs of thermally conditioning the outdoor air. Although little scientific information has been available on the relationships between measured ventilation rates and health symptoms in office workers, a recently collected data set allows investigation of these relationships.
Methods: We performed analyses using data on work-related symptoms and ventilation rates collected by the U.S. EPA from a representative sample of 100 large U.S. office buildings — the Building Assessment and Survey Evaluation (BASE) study. Using multivariate logistic regression models for building-related lower respiratory and mucous membrane irritation symptoms, we estimated relative risks, as odds ratios, for three methods of estimating ventilation rate/person, adjusted for occupancy density and other confounders. The three ventilation rate measurement methods were based on CO2 ratio in airstreams, peak CO2 concentrations indoors, and volumetric estimates of flow rates.
Results: We found a general but irregular association of lower symptom prevalence with ventilation rates above the current recommended minimum for office space (about 20 cfm/person), but found no evidence for further increased benefits as ventilation rates continued to increase above 26, 32, or 37 cfm/person (depending on the measurement method). This relationship, however, did not hold for the volumetric method and lower respiratory symptoms. Also, for all measurement methods, even with ventilation per person held constant, medium to high occupancy density was associated with more symptoms than low occupancy density.
Discussion: These findings suggest, although not with complete consistency, that raising ventilation rates above current recommendations would reduce symptoms in office workers. The inconsistent findings for different measurement methods of ventilation were surprising. Occupancy density may play an unrecognized role in ventilation requirements. Further clarification of these relationships is necessary, as is the validation of accurate methods for measuring ventilation rates.