Capture efficiency of local exhaust ventilation systems.

A new technique to measure the performance of local exhaust ventilation systems has been developed and tested in both the laboratory and the field. The technique involves the measurement of the capture efficiency of exterior hoods, defined to be the fraction of contaminants given off by a process captured by the exhaust system serving that process. Capture efficiency measurement can be a powerful tool in the evaluation of local exhaust systems, since it is a direct, quantitative measure of system performance; in contrast, indices of performance now in use are either qualitative or measure quantities which may not be related directly to system performance. A basic theory for capture efficiency has been developed, and a prototype system for measuring capture efficiency has been constructed and tested. Preliminary laboratory and field measurements using the system have demonstrated the power of the method, which should find widespread use in the design of new ventilation systems and the evaluation of existing ones.