Capture efficiency, eta, is defined as the fraction of contaminant generated which is captured directly by a local exhaust hood. The fraction of contaminant released into the workplace is (1-eta). The release of contaminant is directly related to workers' breathing zone concentration. A model which accurately predicts hood capture efficiency will allow industrial hygienists and ventilation engineers to design local exhaust systems to control breathing zone concentrations at a safe level. Capture efficiency models have been developed recently. These models predict capture efficiency as a function of hood geometry and air flow, location of the source of contaminant, and crossdraft velocity. Turbulence parameters of both the flow field generated by the hood and the crossdraft have not been considered in models developed to this point. The intensity and scale of turbulence affect the dispersion of contaminant around streamlines and therefore, both hood capture efficiency and the subsequent transport of uncaptured contaminant to the breathing zone of the worker. This research proposes to investigate the turbulence parameters of typical industrial flow fields and to modify existing capture efficiency models to quantitatively account for the turbulence level of the flow field.
