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

This research evaluated the effectiveness of screening methods in identifying obstructed branches in industrial ventilation systems. These methods were divided into two categories: pressure comparisons and pressure ratio comparisons. The first category contained techniques that compare measured static pressures with the corresponding design static pressures or with previously measured pressures. Certain aspects of the method suggested in the Industrial Ventilation Manual were also tested. The second category compares the ratios of two measured pressures and includes the new reference ratio method. Data were collected from six industrial ventilation systems. Four of the systems were used to control wood dust, and two were used to control metal shavings from a saw-sharpening operation. Each system was tested for naturally occurring or deliberately inserted obstructions. Appropriate static and velocity pressures were measured to calculate each troubleshooting method's parameter. The change in the parameter was compared with a range of thresholds for the test cases. Receiver operator characteristic curves and bootstrapping techniques were used to identify the best method for determining the presence of obstructions or alterations. The pressure ratio methods were found to be substantially superior to the pressure comparison methods at detecting obstructions.