Study Of The Downward Flame Spread And Combustion Toxicity Of Typical Thermoplastic Materials

With the development of technology and material science, thermoplastic materials are widely used because of their light weight, easy manufacturing and other advantages. But thermoplastic materials have the characteristic of easy to melt and burn, accelerating the fire spread, and generating a large amount of CO and other toxic gases. So the thermoplastic materials have a lot of fire hazards, which seriously affects people’s life, property and social stability. Hitherto, the intensive analysis on the fire hazards of thermoplastic materials is still scarce. To carry out the study on flame spread and toxicity of thermalplastic materials is of important significance both in theoretically and practically, for a comprehensive understanding of thermalplastic material combustion characteristics. It is also meaningful for preventing fire expand and choosing low toxic material. Therefore, a series of experiments were performed to investigate the flame spread behavior characteristics and combustion toxicity of thermalplastic materials in this paper. Based on hierarchical analysis method, the fire risk assessment of thermoplastic material in the flame spread behavior is also studied.A series of experiments are conducted to study the combustion characteristics and the effects of width and thickness on the downward flame spread of thermalplastic materials, while polypropylene (PP) and polymethyl methacrylate (PMMA) are chosen as the representative materials of thermalplastic materials. Many characteristic parameters are measured under different widths and thicknesses, such as flame spread rate, flame height etc. The influence of widths and thicknesses on flame spread rate are discussed combined with heat transfer theory. It shows that the flame spread forms of PP and PMMA are different because of the different pyrolysis mechanism. Due to the comprehensive influence of sample size and mobility, there are some differences in the variation of flame parameters of PP and PMMA.The toxic products is the main factor of killing people in fire. We analyze and compare O2 reduction and combustion products CO,CO2 of PP,PMMA and PE under different fire stages by the steady-state tube furnace (SSTF),and evaluate FED(the fractional effective dose) model of combustion products toxicity. The results show that the maximum combustion toxicity is appeared in the combustion stage of small under-ventilated. The influences of global equivalence ratio (φ) and temperature on the combustion toxicity are also studied. It shows that with the increase of global equivalence ratio and the decrease of temperature, production of CO increases and production of CO2 reduces.Finally, based on the analytic hierarchy process (AHP), the evaluation of PP and PMMA in the downward flame spread process is conducted. The flame height, flame spread rate and toxic gas generation rate are selected as the basic evaluation index parameters to establish a comprehensive evaluation model of fire risk. The single index evaluation and comprehensive evaluation are conducted. Due to the influence of mobility, the fire risk of PP is greater than PMMA. Results are of great significance to enrich the material fire risk evaluation database.