At the Tritium Process Laboratory (TPL) in Japan Atomic Energy Research Institute (JAERI), the three-dimensional "TBEHAVIOR" code has been developed and improved to understand initial tritium behavior and tritium confinement performance in a ventilated room of a fusion reactor in case of tritium leak event. The purpose of this study was mainly focused to; 1) investigate the effect of atmospheric exchange time per hour on the tritium confinement performance in an actual scaled tritium handling room after off-normal tritium release; 2) investigate the effect of atmospheric exchange time per hour on the time necessary for detecting tritium release; 3) investigate the suitable location of exhaust ducts and alarm monitors. The simulated room used in the present analysis is approximately 3000 m3 of tritium handling room (12.00 mW, 29.00 mD and 8.50 mH) with six supply ducts and six exhaust ducts. Atmospheric exchange time per hour is changed as a parameter from 0.67 to 3.33 times per hour.