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.