The paper describes using a vapor degreaser at Wright-Patterson AFB to evaluate various modifications to reduce 1,1,1-trichloroethane (TCA) emissions. The modifications included freeboard extension, refrigeratedchiller, lip vent removal, covers, and combinations of each. The evaluation was aimed at maintaining a safe industrial hygiene environment. The lip vent, installed to maintain the breathing zone concentration of solvent at below the OSHA PEL (permissible exposure limit), also enhanced the discharge of solvent to the atmosphere. The solvent concentration of the discharge duct averaged 300 ppm solvent during normal operation. Freeboard extension reduced emissions by up to 50%, but at the expense of increased breathing zone concentration when the lip vent was off. Using extended freeboard combined with a below-zero freeboard chiller reduced the discharge of solvent by more than 75%, while keeping the breathing zone solvent concentration at 10 ppm and below, although the freeboard fan was turned off. Study results show that both industrial hygiene and air pollution concerns can be satisfied with proper engineering and operation of the degreasing system. The involved degreaser was a 26 sq ft (2.4 sq m), open-top vapor system. Approximately 93,000 lb (42,222 kg) of TCA solvent is used each year in the system. Premodification breathing zone solvent concentration averaged 10 ppm.