This thesis studies the following four topics by CFD simulation. First, the detailed airflow patterns and pressure characteristics of a semiconductor fab were analyzed and verified by available experimental data. Second, both transient and steady state simulations of a fire incidence were conducted to study the influences of fire source volume, fire source altitude, and clean room filter face velocity on the temperature distribution around the vicinity of fire source. Note the temperature distribution at the altitude of fire distinguisher (close to the height of ceiling) is very related to the action mechanism of fire distinguisher. Third, the mean trajectories of various particle sizes in the very early stage of a fire occurrence were simulated to provide substantial information to properly locate the VESADs (very early smoke detect active). Fourth, the performances of three commonly adopted smoke control/exhaust systems for semiconductor fabs were evaluated. An appropriate smoke control/exhaust system is provided and discussed.