This paper describes the measurements of the air change rates and air flow patterns in two large single-cell aircraft hangar buildings. The decay of the tracer gas sulfur hexafluoride was used to measure the air change rates. It was possible to achieve a uniform mixture of indoor air and the tracer gas in the hangars using the air circulation fans of the heating system. Stratified air layers characterized the air flow patterns within the hangars. For the test conditions, measured air change rates for the two hangars are in the range 0.32 to 0.47 air changes per hour. Results also suggest that five sampling locations at about 1.8 m (6 ft) height are sufficient to obtain a representative air change rate for large single-cell buildings. Crown