The recirculation of industrial exhaust air is only one of a number of engineering approaches that can be used for energy conservation. For industry, a recirculation system refers to any ventilation system in which air is removed from an operation, cleaned where required, and reintroduced back into the building. Recirculation has a potentially wide application throughout industry, since it can help reduce the tempering of large volumes of make-up air. Although the practice of recirculation can result in a substantial reduction in the volumes of make-up air required, a safe and healthful workplace must be maintained at all times.