A mode/has been developed to predict dust concentrations in industrial operations that use a recirculated air system. The model accounts for system airfow rates, multiple particle sources, fractional collector efficiencies, and fractional hood capture efficiencies in determining the respirable dust concentration in the working zone. Three examples are considered. One of the examples is used for a parametric study of the recirculated air system. From these parametric studies, it has been found that the hood capture efficiency is the most important factor in the system when high-efficiency dust collectors are used. A 10% change in the hood capture efficiency may change the respirable dust concentration by as much as 50%.