Rabiah and Welkenbach (1993) point out that:
Laboratory fume hood operations vary widely, depending primarily upon the level of activity required for the hood and the work practices of the individuals using the hoods. In an attempt to address these issues, the facilities planning office of a large university initiated a study. This study followed a protocol intended to determine a diversity factor to be used in downsizing the mechanical equipment and establish the concept of a diversity in variable-air-volume system design for laboratory buildings. This diversity factor will provide the backup support to reduce the capital cost of installing VAV laboratory controls.
The study involved six major recently built or renovated research buildings. A total of 300 fume hoods, equipped with variable air volume exhaust/make-up air systems, were randomly selected in the study, and a questionnaire was filled out by each fume hood user. Statistical data, derived from questionnaire answers by students, researchers, and professors, were established on the basis of percent sash opening of each fume hood in hours per day.