| Polyurethane(PU)foam is a versatile ordinary material,often used as thermal insulation material for building exterior facade to reduce energy consumption.Polyurethane used in this paper is light,low thermal conductivity and low cost and many other advantages,however,due to its organic macromolecular compound characteristics and highly flammable,containing large amounts of carbon chain internally,once a burning accident does happens,will produce lager quantities of harmful gas,including carbon monoxide(CO),hydrogen cyanide(HCN),etc.As the fire spreads polyurethane would also create melt-droppong circumstances,which led to many ignition sources,and then along the outside wall of building burned rapidly by the wind.In recent years,because the heat preservation material of the building facade caused fire often came up in interviews,posing a great threat to the safety of people’s property and lives.Consequently,examining typical parameters of fire spread for building insulation materials,will be able to provide technical guidance for fire prevention and fire rescue.In this paper,a double-fire-point reverse fusion experimental device for building insulation boards under variable wind speed conditions is independently designed.According to presence or absence of environmental wind,a series of experimental studies were performed in two experimental conditions.Through analyzing and processing the collected experimental data in the following six aspects,including from flame shape,mass loss rate,thermodynamic analysis,flame temperature,radiant heat flux,and fire spread speed.The experimental results show that the polyurethane foam board softens first and then melts during the fire,afterwards as the temperature rises further,the molten liquid polyurethane evaporates into a combustible pyrolysis vapor.Pyrolysis of combustible vapour instantaneous combustion occurs in contact with the surrounding high-temperature air to keep the fire from spreading continuously.The effect of ambient wind changes the shape of the flame,due to the stretching effect of the wind,the flame length is elongated,and the material surface is applied and tilted.Because the preheating area of the unburned area is increased,the pyrolysis rate of the PU foam board is increased,and the fire spreading speed is accelerated.Besides,compared with the no wind environment,the ambient wind enables the PU foamboard to reach the peak values of its flame temperature and radiant heat flux faster rapidly,the coefficient of the two peaks are also increased.When the dual ignition sources on the left and right sides finally converge and merge into a single ignition source,the temperature linear elevation and then drops suddenly,during this process,the temperature reached its peak,and the temperature on the upper side of the PU foam board always higher than the lower side.Under no wind conditions,the average mass loss rate of the PU foam board’s horizontal reversed dual-source fire spread at the lowest level.As the wind speed increasing,the average mass loss rate of the PU foam board increases firstly and then decreases,when the lateral wind speed is 1.5m/s reaching critical state.Under no wind conditions,the left and right sides fire in the PU foam board spread to the middle at approximately the same speed,under wind conditions,the speed of fire spread on the windward side increases as the wind speed increases,while the leeward side conversely.Similarly,during the spread of fire at the same time,the upper part of the windward side of the PU foam board migrated fastest,while the lower part of the leeward side was slowest.But on the whole,the average fire spreading speed is positively correlated with the lateral wind speed,the average fire spreading speed increases as the wind speed increases.By fitting the image of the relationship between the average fire spreading speed of the PU foam board and the lateral wind speed,the exponential function formula is obtained.Figure [50] Table [6] Reference [113]... |
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