Indoor particles and symptoms among office workers: Results from a double-blind cross-over study

Background. We studied the effects of removing small airborne particles in an office building without unusual contaminant sources or occupant complaints. Methods. We conducted a double-blind crossover study of enhanced particle filtration in an office building in the Midwest United States in 1993. We replaced standard particle filters, in separate ventilation systems on two floors, with highly efficient filters on alternate floors weekly over 4 weeks. Repeated-measures models were used to analyze data from weekly worker questionnaires and multiple environmental measurements. Results. Bioaerosol concentrations were low. Enhanced filtration reduced concentrations of the smallest airborne particles by 94%. This reduction was not associated with reduced symptoms among the 396 respondents, but three performance-related mental states improved; for example, the confusion scale decreased (-3.7%; 95% confidence limits (CL) = -6.5, -0.9). Most environmental dissatisfaction variables also improved; eg, stuffy air, -5.3% (95% CL = -10.3, -0.4). Cooler temperatures within the recommended comfort range were associated with remarkably large improvement in most outcomes; for example, chest tightness decreased -23.4% (95% CL = -38.1, -8.7) for every 1degreesC decrease. Conclusions. Benefits of enhanced filtration require assessment in buildings with higher particulate contaminant levels in studies controlling for temperature effects. Benefits from lower indoor temperatures need confirmation.