The use of exhaust air recirculation to conserve energy was analysed. Recirculation decision logic, design and assessment, worker exposure, and system evaluation were outlined. Recirculation without premixing, air recirculation system monitoring, and recirculation air bypass were described. Costs, safe exposure concentrations, dilution, monitoring devices, systems flexibility, airflow rates and patterns, ventilation, and air cleaner efficiency calculations were discussed. The authors conclude that adherence to these guidelines is necessary, and caution that if the air contains human carcinogens, recirculation should not be attempted.
Division of Physical Sciences and Engineering, NIOSH, Cincinnati, Ohio