Engineered Local Exhaust
The early development of the technology of local exhaust began around 1928 with academic attention being paid to the air patterns developed by hoods intended to capture dust particles. The environment within which a local exhaust system is employed can affect its efficiency to a considerable degree. Exhaust hoods used in local exhaust systems are in close proximity to the process operation. Multisource systems are more common and have the complication of seeing that the proper air is exhausted from each exhaust hood. Exhaust air controls the movement of air into the chamber but in a pattern that does not cross the falling material, thereby avoiding removal of excessive production material. The chapter focuses on the exhaust hood, the design of which is the key to successful engineered local exhaust. Good duct design includes the use of wide radius elbows; flanged and sealed connections; and grounding to avoid the build-up of static electricity charges.