ABSTRACT
This chapter provides useful information on the selection and operation of hoods and exhaust systems that can make this facility safe and liveable. Experience has shown that the most reliable, flexible, and easiest to maintain system is that in which an adequate supply of outside conditioned makeup air is provided to the laboratory to balance the air being exhausted. Air exhausted from a hood is never recirculated so that hood burden goes up. The relative cost of air conditioning is low because the amount of room air exhausted is reduced. All hoods should be equipped with safety devices such as a sail switch to warn personnel that the air volume exhausted from the hood has dropped to a point where it will not provide sufficient capture velocity for safe operation. The accepted method for containing and removing fumes, odors, and other contaminants emitted from laboratory work or chemical testing procedures is to restrict the operations to an enclosure.
