A Study On The Smoke Movement Pattern And Smoke Control In High-rise Building Fire

With the contradiction between population explosion and limited land in urban area increasing, high-rise building is an inevitable choice for urban development. High-rise building has the characteristic "six more" that stories, interior finishing materials, electric installations, functions, pipe shafts and the staff are more. Due to these characteristics, it will spread rapidly once fire occurs and personnel evacuation and escape will become a hot potato. According to statistics available, more than 70 percent of casualty is choked to death by smoke in high-rise building fire. Therefore it is very significant to study on the smoke movement regularities and smoke control in high-rise building fire.Evacuation by stairs takes long time and leads to congestion and confusion easily in high-rise building fire. Also it is difficult for personnel evacuation and escape. It has great capacity for descending personnel evacuation by elevators. With the development of science and technology and the improvemt of management, advantages and possibilities of evacuation by elevators is increasingly outstanding. Based on the theoretical analysis of piston effect and its influence on smoke, hoistway pressurization, lobby pressurization and pressure fluctuations are analyzed. The pressure difference between lobby and building is dependent upon the piston area-rate, elevator car velocity, the flow paths and position of elevator car. The regularities of air flow between the shaft, the building and the outside are analyzed which is caused by elevator piston effect in high-rise buildings with pressurization and without pressurization. Thus we can determine the critical mass flow rate that smoke infiltration into the lobby can occur. For most modern elevators, especially those in multiple car shafts, it is feasible to deal with the piston effect by designing so as to prevent smoke from being pulled into the lobby. Smoke can be kept under effective control with reasonable smoke control systems to improve the safety of evacuation by elevators.Numerical model is established with field model FDS and smoke movement is simulated in high-rise building fire. Based on simulated results, factors influencing effect of natural smoke exhaust, mechanical smoke exhaust and lobby pressurization are analyzed. Factors influencing effect of natural smoke exhaust include heat release rate of the fire source, position of the fire room, size of windows and length of corridor. Factors influencing effect of mechanical smoke exhaust include smoke extraction volume, position and number of smoke vent, position of the fire room etc. Factors influencing effect of lobby pressurization include the position of the fire, air output supplied by pressurization, the stories that open doors, the storey that the elevator door open and the position of the fan etc.Natural smoke exhaust is subjected to the position of the fire room, plane layout of the building and size of windows. When the fire is located at one end of the corridor, smoke produced by the rapid growth of fire can't be exhausted by the nearby window and the remote window can't play an effective role in exhausting smoke. When the fire is located at the middle of the corridor, it accelerates exhausting smoke, therefore smoke exhaust is relatively stable. Effect of natural smoke exhaust is improved obviously when the height of windows is increased. Shorter corridor makes natural smoke exhaust more effective. Natural smoke exhaust is more effective as auxiliary facilities when corridor is much longer in high-rise building.Effect of mechanical smoke exhaust is more stable, not subjected to natural factors. To increase smoke extraction volume per unit area will improve its ability to remove smoke. Effect of smoke exhaust is more stable when smoke vent is located on ceiling than on sidewall. Sidewall smoke exhaust is directly bound up with the clear height from floor to smoke vent, but it is not suitable because the ceiling is only 2 meters high in practice. Considering the model, mechanical smoke exhaust is not much restrainted by the number of smoke vent for straight corridor. But a concrete analysis should be made for other buildings with diffierent construction patterns to make sure that mechanical smoke exhaust is effective. For straight corridor, it is better when the fire room is located between the two smoke vents than located at one end with the same smoke extraction volume.In the floors below the fire floor, the pressure of the elevator door crack and the lobby increases as the floor ingcreases. In the fire floor, the pressure of the lobby decreases quickly due to pressure loss caused by opening the lobby door. In the floors above the fire floor, the pressure of the lobby decreases as the floor increases. The pressure of the lobby and pressure differences across the elevator and lobby door increases as the air output supplied by pressurization ingcreases. When the air output is 4m3/s, the pressure difference keeps at about 60-80Pa. When the air output is 5m3/s, it keeps at about 120Pa. When the air output is 6m3/s, it keeps at about 180Pa. Opening the lobby and elevator door is apt to cause pressure loss, so personnels in the building should avoid opening doors in the fire floor and its adjacent floors and evacuation by other floors can be considered. The floor above or below the fire floor can keep at positive pressure even its lobby and elevator door is opened. If the lobby and elevator shaft can keep at a certain positive pressure with pressurized smoke control system, elevator can stop at the floors except the fire floor so that personnels in the building can be evacuated by elevator.The results provides a certain theoretical instructions and technical support for effective control of smoke, smoke control design, personnel evacuation and fire fighting in high-rise building fire.