An evaluation of industrial ventilation branch screening methods for obstructions in working exhaust systems

This research evaluated the effectiveness of screening methods in identifyi ng obstructed branches in industrial ventilation systems. These methods wer e divided into two categories: pressure comparisons and pressure ratio comp arisons. The first category contained techniques that compare measured stat ic pressures with the corresponding design static pressures or with previou sly measured pressures. Certain aspects of the method suggested in the Indu strial Ventilation Manual were also tested. The second category compares th e ratios of two measured pressures and includes the new reference ratio met hod. Data were collected from six industrial ventilation systems. Four of t he systems were used to control wood dust, and two were used to control met al shavings from a saw-sharpening operation. Each system was tested for nat urally occurring or deliberately inserted obstructions. Appropriate static and velocity pressures were measured to calculate each troubleshooting meth od's parameter. The change in the parameter was compared with a range of th resholds for the test cases. Receiver operator characteristic curves and bo otstrapping techniques were used to identify the best method for determinin g the presence of obstructions or alterations. The pressure ratio methods w ere found to be substantially superior to the pressure comparison methods a t detecting obstructions.