Cost benefit analysis of local exhaust ventilation systems

Abstract

The objective of this investigation was to demonstrate that a cost benefit analysis approach, a versatile decision making tool, can be utilized by the Professions of Industrial Hygiene and Safety Engineering to justify costs involved in developing and implementing engineering controls of occupational exposures to physiologically harmful materials and/or conditions. A simplified and adaptable step-by-step cost benefit analysis approach is presented in this dissertation. To illustrate the efficacy of this approach, a local exhaust ventilation system was analyzed using a cost benefit analysis method. An experiment was conducted to evaluate the effects of three variables on the total cost (initial cost + continuing operating costs) of a local exhaust ventilation system. These variables were: 1. The cross section of the duct work (circular and rectangular ducts), 2. The radius to diameter (R/d) ratio of the elbow, and 3. The angle of entry of the branch duct into the main duct of the system. Two local exhaust ventilation systems, one with circular ducts and the other with rectangular ducts, identical in all respects, were designed, constructed and evaluated. For both systems, three 90° elbows, one each with R/d ratio of 1.5, 2.0 and 2.5, for the main duct and four angles of entry of 30°, 45°, 50° and 90° were used for the branch entering the main duct. The angles of entry were through properly designed expansion joints. Experiments were performed for capture velocities of 100, 125 and 150 feet per minute at distances of 6, 9, and 12 inches from the main duct opening at the centerline for each velocity.