Abstract: Smoke movement is numerically simulated using FDS (Fire Dynamic Simulator) developed by NIST in a clean room with an upper-supply and bottom-exhaust air-conditioning system. The velocity field and temperature distribution in the early stage of a fire is analyzed. The effect of the air flow pattern on smoke movement as well as the effect on early stage fire detection are discussed. The temperature and concentrations near the ceiling are affected significantly and the detector activation time will be delayed for dozens of seconds compared with that of the room without air-conditioning systems.

Key words: smoke, detector, air-conditioning system, clean room, airflow pattern