Studies On The Inhibition Mechanism Of Vertical Ejecting Fire Spread Under Different Building Facade Fire Protection Constructions

For a fully developed under-ventilated compartment fire, the hot gases and smokes with flame eject from the facade broken window that caused by hot pressing and high temperature radiation. Thus, the special phenomenon of flame ejecting behavior has been formed. The hot gases and smokes with flame spread to upper floors under the effect of buoyancy, and burst the upper floors glass, leading to further spread of the fire to adjacent floors. In this case, the three-dimensional building fire spread is finally developed.The flame ejecting behavior is the initial stage of formation the three dimensional flame spread. It is very necessary to inhibit the vertical fire spread and avoid the formation of three-dimensional fire, depending on the fire protection construction itself, not only improving the fire-resistant level of the building facade. Because the shape of flame ejecting behavior is not the same under different fire protection constructions, the temperature distribution of the combustion chamber and building facades and heat transfer characteristics (such as heat radiation and heat convection, etc.) are also different. In order to ensure the fire safety of high-rise building, Grasping the building facade fire occurrence and development mechanism, determine the appropriate fire protection technical requirements, and developing the fire protection construction method to inhibit the vertical spread of ejecting fire, according to the actual situation of construction, have become issues needed to be resolved in the field of fire safety.This paper presents experimental investigation, numerical simulation research and theoretical analysis on flame ejecting behavior upon building facade under different fire protection constructions. A series of experiments for different window size, window aspect ratio, vertical position of the window, the width of the fire canopy, fire canopy’s position, as well as the source of fire power were carried out by using test facility and simulation software, to study on the block mechanism of fire spread vertical. At last, combined with the width of fire canopy, the height of wall between the up and down windows and window size, the calculation method of building facade temperature distribution and the optimum combination schemes with specified range of use were put forward to inhibit the vertical spread of building facade ejecting fire. The specific work includes the following four aspects:(1) Reduced scale model of 1:2 was designed and established as fire simulation test facility. The test bench consists of adjustable window, adjustable fire canopy, stair, side door and temperature measuring system. In order to study the behavior of the building facade ejecting fire under different fire protection construction restrict conditions, and reveal the regulations of the distribution temperature inside the combustion chamber and above the building facade, the window size, vertical position of the window and the width of the fire canopy were altered.(2) The behavior of building facade ejecting fire and characterization of the mathematical model under free boundary conditions were revealed. We conduct the investigation on influence mechanism of the flame ejecting behavior and measure the distribution of temperature inside the combustion chamber and above the building facade, considering emphatically window aspect ratio and vertical position of the window, not only the ventilation factor. Based on the energy conservation equation, the model of average temperature distribution inside the combustion chamber was revealed. Coupled the factor of window aspect ratio, the dimensionless overflow heat release rate and the model of temperature distribution under free boundary conditions were proposed.(3) The behavior of building facade ejecting fire and characterization of the mathematical model under fire canopy restrict conditions were revealed. Firstly, the temperature profile inside the combustion chamber and above the building facade was studied by changing the fire simulation test facility in width of the fire canopy. Then, the characteristic parameters (temperature profile inside the combustion chamber and above the building facade, thickness of ejecting flame, horizontal velocity of ejecting flame and overflow trajectory) under the different of position of the fire canopy and the power of the source were illustrated by numerical simulation method. Based on the above research, the dimensionless temperature gradient was introduced here to establish the model of building facade temperature distribution under fire canopy restrict conditions.(4) Put forward the combination plan to inhibit the vertical spread of building facade ejecting fire. Considering the model of temperature distribution established above and numerical simulation software, the feasibility study that inhibit the vertical spread of building facade ejecting fire was executed, while the distance of the wall between windows and the widenth of the fire canopy less than the specification requirements. The process of predict the temperature distribution of building facade was established, and meanwhile, combination plan that inhibit the vertical spread of building facade ejecting fire was proposed, considering the influence of fire canopy and wall between windows under different overflow heat release rate.In this paper, the research results are benefits to understand the basic principles of building facade ejecting fire under different fire protection constructions. The combination plan that inhibiting the vertical spread of building facade ejecting fire was proposed, and can effectively reduce the fire risk of the building facade and the probability of serious fire accidents. At the same time, the research results can provide a theoretical fundation for fire protection designer to design the building facade, and have reference value and guidance significance to revise the related content in the National Norm of Building Fire System.