In densely populated urban areas, in the event of the toxic gases leak, how to accurately determine the risky zone and take effective measures to evacuate inhabitants quickly out of dangerous areas and minimize the unexpected losses is a tropical topic in China. First, the ALOHA code defined any interested accidents scenarios. For any different exposure times and concentrations, the distances down wind direction could be determined, which eventually generated the dead zone, wounded zone, injured zone and evacuation zone. Then, it presented the procedure of an emergency evacuation routes selection, the choice of the principle of refuges and shelters for evacuated inhabitants, as well as evacuation traffic organizations, vehicle assignments, real-time communications and other traffic evacuation strategies. Finally, the OREMS code was proposed to study the sudden leak accident and design emergency response policies (ERP). A sudden gaseous leakage incident in Tianjin Olympic stadium was chosen as an example to verify the raw ERP including the evacuation road network design, the evacuation time for vehicles, vehicle running conditions and the possible road congestions. Results showed that when the radium of the emergency evacuation scope is about 3 km, the time for evacuation of 50% vehicles is proper. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.