Study On Radiation Law Of Open Fire Overflow In Different Directions With Distance

With the rapid development of China's economy,people's living standards and needs are increasing,and there are more and more accumulated combustibles in our homes and offices which will led to a significant increase in fire safety hazards.In particular,large-sized fire accidents have occurred frequently in recent years,which have a great impact on people's work and life,and will often lead to terrible injury or death or huge property losses.When a fire occurs in building,it often spreads outside of the building by the window or door of the room.The flame overflowing from the opening transfers heat to objects around the opening by radiation,and poses a great threat to combustibles in nearby rooms,floors or even the opposite buildings.When the radiation intensity reaches a critical level,it can not only ignite flammable materials without contacting each other,but also can cause discomfort or even death accidents.At present,the research on the external fire of the building mainly focuses on the height of the flame and the influence of the opening on the flame spread.There are few comparative studies on the influence of radiation in different direction of the opening and the opposite building.Therefore,it is necessary to study the spread law of radiation intensity in external building fires to know more about of the safe critical distance for human body and combustibles under different conditions.Many domestic and abroad scholars have already conducted researches on flame overflow,mainly focusing on the characteristics of flame overflow and its various influencing factors,including opening factor,wind speed,emissivity and so on.There are few studies on the influence of radiation distribution.At the same time,considering the difficulty of replicating the disaster situation,this paper uses the FDS(Fire Dynamic simulator)software to simulate the fire in the building with an open which is 2 meters wide and 1 meter high.And the burning rate is based on the real fires accident,the variation law and difference of external radiation intensity in the three typical directions of external:vertical,horizontal and radial of the fire chamber are compared.It is concluded that the radiation intensity in three typical directions is positively correlated with the power of the fire source and negatively correlated with the distance.The vertical direction is most affected by the power of the fire source and the distance,followed by the horizontal direction and the radial direction.In the vertical direction outside the opening,the radiation intensity conforms to the semi-Gaussian distribution,and as the power of the fire source increases,the height of the radiation attenuation increases.In the horizontal direction,the radiation intensity conforms to the Gaussian distribution,but the results on both sides are not equal all the time due to the flame fluctuation.In the radial direction,the radiation intensity accords with the exponential distribution,and the empirical formulas of the radial radiation intensity of the fire floor and the upper layer with greater radiation influence are obtained respectively.Finally,the critical distance in different fire source power for people and objects are proposed.On the other hand,based on the building fire code and the common building spacing conditions in the real situation,the change of the fire building itself and the adjacent building's external radiation intensity with different distance are studied,and the result is compared with the single building.It is obtained that for the adjacent buildings,the change of the building distance does not have much influence on the indoor combustion of the fire building itself,but the combustion around the opening were influenced.As the distance between two buildings decreases,the change of the radiation intensity outside of the fire building itself is not obvious.If the distance is reduced to a 2-3 meters,the flames from the opposite building will cause the flame fusion to have a strong influence on the radiation intensity.For the opposite building,there were combustibles right behind the window.The relationship between the radiant heat accumulation velocity of the combustible surface and time is obtained.Comparing the single-building and adjacent buildings,the distribution of the external radiation intensity shows that the existence of the opposite building will affect the entrainment condition of the flame outside of the building,and the flame burning condition near windows is suppressed.The external radiation intensity of the adjacent buildings is lower than that of one building.