Improved local exhaust control by directed push-pull ventilation system.

Experiments using the directed push-pull ventilation technique were conducted on a general type of local exhaust ventilation installation. The exhaust (pull) system consisted of a square hood, while the push system consisted of one or two slot jets or two round jets. The two slot or round jets were located behind and beside a mannequin (the mannequin simulated the worker's position). The one slot jet was located between the smoke source and the mannequin. Under experimental conditions, the push-pull system reduced the amount of smoke in the mannequin's breathing zone even when the exhaust system volume flow rate necessary for capture of the smoke decreased approximately 50%. Generally, no difference between the slot and round jet control performance was found. The experiments showed that the directed push-pull ventilation system can be used effectively to reduce the contaminant emission into a workroom, if the jets are located so that the eddy currents induced by the worker or other obstructions are minimized or eliminated.