Recirculation of Exhaust Air -- An Overview.
NIOSH 1976 Feb:5-24
A study to develop technical performance criteria for recirculated exhaust air systems is described. These criteria reflect contaminant toxicity, the requirements for air monitoring and air cleaning equipment, reliability analyses of fail-safe systems, and theoretical modeling of system performance. Based on contaminant toxicity, 356 of the 514 compounds that are listed in the body of the American Conference of Government Industrial Hygienists- Threshold Limit Value table are potentially recirculatable. Carcinogenic compounds and compounds with ceiling concentrations are to be excluded from recirculation systems. Air monitoring equipment should be online, automatic, and specific for individual contaminants. Reliability analyses indicate that recirculation systems that incorporate backup or redundant air cleaning equipment have a lower probability of failure for all operating times that systems without backup. Systems without backup air cleaners should contain provision for exhaust bypass to the atmosphere in the event of an air cleaner or monitor failure. Analytical recirculation models are developed to predict the transient response of workroom concentration as a function of contaminant gereration rate, room volume, general and recirculated air flows, and the air cleaner and local exhaust hood capture efficiencies. The effect of air cleaner failure and bypass of exhaust air to the atmosphere are also modeled.
Air-quality; Air-contamination; Circulation; Control-measures; Toxic-substances; Carcinogens; Environment; Safety-engineering; Contaminants; Ventilation-systems;
Recirculation of Exhaust Air, Division of Physical Sciences and Engineering, NIOSH, HEW Publication No. (NIOSH) 76-186