The advisability of having a recirculation exhaust system is discussed, the merits of various systems, system components, component arrangements, controls and monitoring arrangements are considered and, finally, operating and maintenance procedures are examined. It is brought out that the two most important factors in the design of recirculation exhaust systems are safety and energy conservation. A photograph of a typical heat recovery centrifugal is given, a maximum heat warmup cycle is diagrammed, air cleaning equipment recommended for various industrial processes are listed, as are labroatory test determinations for major contaminants, the relative adsorptive ability of activated carbon filters for several compounds are listed and diagrams of cleaning systems are given. Of the 514 chemical compounds commonly found in the industrial workplace and for which the American Conference of Governmental Industrial Hygienists has established threshold limit values, 94 have been classified as not potentially recirculatable and an additional 64 are not recommended for recirculation systems. Cleaners and monitors have been established for only 68 of the remaining compounds. It is emphasized that each recirculation exhaust system must be based upon the contaminants produced by the industrial process being considered, and sufficient data are considered available to allow a conservative approach with all potentially recirculatable compounds.
Recirculation of Exhaust Air, Division of Physical Sciences and Engineering, NIOSH, HEW Publication No. (NIOSH) 76-186