Study On The Evolution Of Fire In The Confined Underground Space

Since the 21st century,with the rapid development of global economy and the accelerating process of urbanization,the underground space becomes an important part of urban construction.Due to its special structure,underground space fire brings more serious damages,as well as new problems and challenges for fire safety.Especially in the underground parking garage and other special underground confined space,the environment is relatively close in structure and there are many flammable substances inside,the fire evolution in confined underground space presents special rules.A3.6m×1.5m×1.5m small experimental models is set up in this paper with 0#diesel oil as fuel under the condition of natural ventilation.Based on the test and analysis of the fire flame temperature,hot smoke layer temperature and the radiation heat flux near the fire source on the floor,the evolution process of fire in the underground confined space is analyzed.First of all,in natural ventilation environment,800 ml,900 ml,1000 ml of diesel is placed in the 500 mm diameter of main oil basin respectively,and a 145 mm×145 mm×3 mm rubber is placed in the auxiliary fuel pan in 200 mm diameter.Experiment results illustrate that the strong heat storage capability and the confined underground space cause the huge accumulation of fire flue gas in the confined underground space,the thermal radiation of flame and hot gas layer,as well as the wall heat feedback makes a dramatic increase in the temperature of the fire,burning into the vigorous stage,the main oil basin oil flame root size is beyond its diameter,the behavior of the flame has spread from the fuel surface,which illustrates as a ghosting fire.When the upper hot smoke layer temperature reaches 450?,the radiant heat flux accepted by the floor reaches 17 kw/m2,the rubber in the auxiliary fuel pan was ignited,which marked the flashover phenomenon.The underground confined space fire experiments show that in the process of fire evolution in the relatively closed environment and strong heat resistance space,much heat and smoke are unable to escape,which make the whole space temperature rise sharply and make it extremely easy to the formation of flashover critical condition.Furthermore,the fire dynamics simulation software FDS is applied to analyze the fire evolution rules in the confined underground space.A 18 m×6.9 m×2.9 m underground space fire model is established,the evolution process of fire is simulated and compared with the experiment results.The results found that the early fire stage coincides a lot with each other,but after the occurrence of flashover in the simulation,fuel combustion are greatly influenced by ventilation environment,and illustrates unstable combustion state of fluctuation,swim conflict phenomenon found in this one phase at the same time.And in the same conditions of fire area,by changing the natural vent size,it is found that the emergence time and duration of ghosting fire is not a simple relationship with the increase of the natural ventilation opening size,the increase of fire source area improves the fire heat release rate,resulting in ghosting fire more easily.Ghosting fire means the serious spread of fire,especially in the confined underground buildings with high density of fire load.In the further numerical simulation study,water mist suppression of the underground space fire is processed.Results show that under the direct effect of water mist,the fire heat release rate is reduced in straight line,the temperature of in the whole of the limited underground space is reduced simultaneously,inhibiting the flames in the natural air vents.Under the effect of water mist,the scope of fire and the formation of the fire behavior of more complex is controlled.