Effects Of Density And Inclination On The Characteristics Of Ignition And Flame Spread Of Thermal Insulation Material Of Expanded Polystyrene

In recent years, due to the small thermal conductivity, light weight, low cost, low water absorption, high damp-proof property and other advantages, the thermal insulation material of expanded polystyrene(EPS) was widely used in exterior protected construction of different buildings,Such as wall insulation system in energy-saving buildings and sandwich panels in the wall of prefabricated house. However, EPS also had a high fire risk. At present, the fire characteristics of thermal insulation materials of EPS had been widely investigated and had made some achievements. Nevertheless, there were few studies on the characteristics of ignition and fire spread behavior of EPS under different conditions(density, width and angle of inclination). Meanwhile, the research on the related characteristic parameters wasn't deep enough. Therefore, in order to provide a certain basis for the evaluation of the fire hazard of EPS, it is necessary to carry out the corresponding experimental research, to further improve and reveal the fire hazard of insulation material EPS.In this paper, a series of lab-scale experiments was carried out with the densities of 6 kg/m3, 10 kg/m3, 15 kg/m3, 18 kg/m3 and 25 kg/m3, and widths of 4 cm, 8 cm, 12 cm and 16 cm respectively, to investigate the characteristics of ignition and flame spread of EPS. The results show that, the EPS's fire zone was divided into two parts including the surface fire zone and the pool fire zone, and the flame structure of EPS during flame spread process includes the typical type, the vertical type, the reverse type and the merged type. When the densities of EPS samples were 6 kg/m3 and 10 kg/m3, both the density and width of EPS had a great effect on ignition time, and it's difficult to maintain a stable flame spread process after ignition process. When the densities of EPS were 15 kg/m3, 18 kg/m3 and 25 kg/m3, the ignition time are similar between different EPS samples, and it could maintain a stable flame spread process. Both average length of pool fire zone and average height of surface fire zone of 15 kg/m3, 18 kg/m3 and 25 kg/m3 EPS samples were first increasing then decreasing with the rise of the density. In addition, for the density of 15 kg/m3, both the average length and the average flame height of pool fire zone of EPS samples were increasing with the rise of the width, and the average fire spread speed was fluctuates up and down with the rise of the width; for the density of 18 kg/m3 and 25 kg/m3, both average length and average flame height of pool fire zone of EPS samples were first increasing then decreasing with the rise of the width, same with average fire spread speed change rules with the increase of the width.Meanwhile, a series of lab-scale experiments was carried out with the angles of-30°,-20°,-10°, 0°, 10°, 20° and 30°respectively, to investigated the effect of the inclination on the characteristics of ignition and flame spread of EPS samples. It is found that, EPS samples go through three stage including the initial stage of solid phase, the preheating stage and the fire stage. Meanwhile, the preheating stage was consist of three parts including the shrinkage deformation stage, the molten stage and the pyrolysis stage. So we can know that, condensed phase structure of EPS samples including the solid phase zone, the contraction molten zone and the pyrolysis zone. And both the flame angle and the pyrolysis angle were decreasing with the increase of the angle of inclination. But the average flame spread speed of EPS sample was increasing in the same time. More over, the maximum length of pool fire zone of EPS samples was first decreasing then increasing. In the downward flame spread process, the flame length of surface fire zone was decreasing with the increasing of the angle of inclination;and in the horizontal flame spread process, the flame length of surface fire zone was increasing rapidly; and in the upward flame spread process, the lame length of surface fire zone was first decreasing then increasing with the increase of the angle of inclination. Furthermore, based on basics of both heat transfer theory and combustion theory, a downward flame spread model and a upward flame spread model were established, so that we can study the inherent law during the flame spread process.