Fire safe elevator used for evacuation in supertall buildings

Abstract

Full evacuation is a key concern for supertall buildings due to the high population density and long travel distance. Using the elevator would speed up evacuation but there are fire safety concerns. In this thesis, fire safe elevator system for evacuation in supertall buildings is studied. Evacuation times in tall and supertall office buildings are estimated first by empirical expressions and software. The estimated evacuation time would be very long even if the evacuation design is based on the specifications in the fire codes. Evacuation by elevator is recommended and a new design is studied. Numerical studies are carried out to evaluate the fire hazards of this design in an example supertall building. Storing large amounts of combustibles in supertall buildings might cause big fires, particularly under wind. The heat release rate (HRR) could change significantly for the same load of combustibles under different ventilation conditions. Therefore, HRR in room fires is studied vigorously in this thesis by the Computational Fluid Dynamics software Fire Dynamics Simulator (FDS). Key points on applications of free boundary conditions and grid sensitivities are evaluated. Results measured from full-scale burning tests on wood and gasoline fuel in a room calorimeter are used to justify the numerical results. The effects of ventilation factor on HRR and mass flow rate through the door opening are analyzed. Some supertall buildings, especially residential flats, have openable windows on balconies for natural ventilation provision. Strong wind at height would supply more air to burn the fuel and hence give rise to a bigger room fire at higher levels. The geometric properties of fire plume and smoke movement under different wind speeds are simulated by FDS. The predicted results show that the lateral spread of flame and smoke is proportional to wind speed both in the leeward and cross-wind direction. Wind effects on HRR of wood chipboard with a gasoline fire in a room with opposite wall openings are investigated numerically. Results show that wind speed affects HRR changes at different stages of the fire. A design of fire safe elevator system combining the refuge place with fire safe elevator is studied. A variety of factors, such as the complex structure of the rooms in the supertall buildings or wind effect, can significantly affect HRR for the same load of combustibles. Therefore, in the proposed design, fire safe elevator is surrounded by the refuge places with at least 2 hours fire resistance rating. During the fire, the elevators would be controlled to stop only at the storeys with refuge places. This arrangement can protect both the occupants and the elevators. Occupants can first evacuate to the refuge places, and then take elevators to evacuate from the refuge places to the ground quickly. In this way, occupants can have a better psychological feeling on using the elevators in the refuge places in a fire incident. Smoke spread to the system is also considered. The effect of ventilation of the shaft, stack effect and wind effect in the system are studied by theoretical equations and FDS. Different arrangements of smoke extraction with pressurization systems are evaluated by analyzing the smoke dispersion and pressure distributions in this fire safe elevator system. Finally, the effect of location of the fire floor in the building on smoke spread is investigated.