The Study Of Wind Effect On Flame Spread Behavior Of Polystyrene Insulation Materials

Since the organic external insulation materials have the characteristics of low thermal conductivity, low density, high corrosion resistance, etc. They are widely used in building facades, such as polystyrene insulation board, polyurethane rigid foam board. However, organic insulation materials, for example the polystyrene insulation material, are easy to ignite. Once the fire occurs, the flame will spread fast, and the combustion process will releases large amounts of toxic and noxious fumes which makes it be a great risk for the people. In recent years, the fire caused by the building’s exterior insulation materials happened frequently. The flame spread behavior, the phenomenon of combustion and the flame-retardant properties of the insulation materials have drawn the attention of researchers. At present, more and more studies were about the effect of environmental pressure, samples angle, sample size and other aspects on the insulation materials flame spread. Few studies discussed the effect of the opposed environmental wind during the insulation materials fire spread which closely related to the real fire. This paper intended to study the flame spread of polystyrene insulation material in opposed environmental wind at the very beginning. While the pyrolysis angle appeared during the horizontal flame spread, thus a new study point was introduced. This study focused on two major research points as follow:(1) The study of flame spread over polystyrene insulation material without external wind. To explore the effect of external wind on polystyrene insulation material during flame spread, a large number of small scale experiments without wind were carried out firstly. In this part, the study not only focused on the basic parameters of the flame height, the temperature, the rate of fire spread, but also paid close attention on the new study point pyrolysis angle. The relation between the angle and flame spread rate was investigated. The results show that the dimensionless flame height and the sample width displays a negative-power function which means the dimensionless flame height shows a downward trend with the sample width increasing. The pyrolysis angle and fire spread rate is negatively correlated with the width increasing. And the pyrolysis angle first decreases and then increases, however the flame spread rate presents the inverse law. The extreme point is obtained at the with size of 8 cm. The width of the sample has affect on the heat transfer mechanism, which leads to the changes of the parameters above.(2) The effect of opposed wind on the inclined flame spread over polystyrene insulation material. The width dimension of 6 cm polystyrene insulation material sample was selected. The direction of the opposed wind was horizontal, the value of the wind was various and the inclined angle was various from horizontal to vertical. The results reveal that, regardless of how the sample tilt angle changes, the dimensionless flame height and Froude number shows a negative power function, and thus it can be obtained that the dimensionless flame decreases with the speed of opposed wind increasing. While the value of flame spread rate at different conditions shows some diversity, which is mainly due to the coupling effect of the opposed wind and the inclined angle which leads to the different of the heat transfer mechanism. The environmental wind affects the sample thermal convection and thermal radiation, and then makes the rate of flame spread changes. Because the polystyrene insulation material is a kind of thermoplastic material, the solid material become molten liquid first during the combustion process. When the inclined angle of the sample is small, the molten liquid does not change the basic position due to the existence of friction between sample and ceramic fiber. While, when the inclined angle is large enough, the gravity downward along the inclined surface of the molten liquid will be larger than the friction which causes the molten liquid volume roll down. Thereby the rolling molten liquid makes the mandatory heat conduction occur at the flame front which accelerating the rate of fire spread. In addition, it could be obtained that the squares of the opposed wind speed was a function of the non-dimensional flame spread rate, and the value of flame spread rate decreased with the wind speed increasing.