Study Of Fire Suppression Mechanism Of Water Spray On Typical Building Facade Material Flame Spread

For the past few years, high-rise building fires have become one of the most disastrous accidents that threaten the personal and property security of urban residents. The combustible material used in building exterior construction and decoration is one of the key parameters that lead to building facade fire spread. Since it always links to fast fire propagation, the upward flame spread is the most rapid and most hazardous, among upward flame spread, lateral flame spread and downward flame spread. As the requirement of improving fire safety condition and reducing potential fire loss in high-rise building, it is important to investigate the fundamental principles of the fire spread mechanism and the applicable fire suppression technique of high-rise buildings. Water spray is one of the most efficent methods for fire suppression of morden buildings. Fire water supply of high-rise buildings is limited and difficult to guarantee. The exploration of water spray fire surression mechanism on building facade fire spread has significance for building exterior water spray system study.To understand the basic law of upward flame spread, this work first carried fire spread experiments to obtain the basic characteristic of ignition, combustion and flame spread behavior of typical building exterior combustible material, which provided the fundamental reference for application of water spray fire suppression system. Typical sample used in present work is polymethyl methacrylate (PMMA), which is one of the most common building adornment materials. On this basis, water spray systems that could be used to suppress flame propagation was designed and developed. The fire suppression efficiency and detailed rules of its influence was further analyzed. This provided necessary guidance for the development of building exterior water spray systems. The specific contents this work focus are as follows:Theoretical analysis and discussion of the ignition process, combustion behavior and fire spread process of building facade combustible was carried out to understand the basic rules of combustion and fire spread on building exterior wall. Model used to predict the relationship between ignition time and external heat flux was developed and was further confirmed with experiment. For the flame spread process, relationship between average flame height and heat release rate was analyzed and discussed both theoretically and experimentally. Besides, the functional relationship between average flame spread and average pyrolysis height, and the accurate solution of theoretical model regarding pyrolysis height and burning time were also discussed. The results from the experiment verified the analysis and proved the reasonability.For the fire suppression process, water spray system which was applicable for the experiment scene was developed and was used to study the fire suppression effectiveness. This mainly includes the influence of different spray discharge angle, spray pressure and water supply. Results showed that for combustion process, cooling effect of spray droplet on the burning surface was the main mechanism of the fire extinguishment behavior. The spray discharge angle affected the effective action area. And as a result, the extinguish time decreased with the increase of spray discharge angle. For burning samples with large aspect ratio, the fire extinguishment mainly relied on the water film formed on the burning surface. Heat was exchanged via water flow through conduction and convection. Result showed that the key parameter of this process was spray flow rate. In addition, numerical analysis was carried out to supplement and verify the experimental results. The discussions included the influence of different flow rate and spray parameters on wall surface temperature, flame height and pyrolysis height. Results predicted by the model agreed with data obtained from experiment. This further provided reference for actual water spray system design and development of modern high-rise buildings.Based on the above theoretical and experiment work, building facade water spray system based on water curtain spray was discussed. To verify the practicality and reliability, the fundamental characteristic of water curtain and the spread behavior of water film on vertical wall were analyzed first. To solve the high energy loss problem of existing spray nozzle, a new kind of curtain nozzle based on centrifugal and deflector was designed. In the end, one type of designing scheme of building exterior water spray system was presented and the quantitative analysis of its feasibility was proved to be workable.