Studies On The Charateristics Of Heat Melting And Downward Flame Spread Of The Organic Insulating Materials

With the increasing interest in energy utilization and saving, external wall insulation materials are expected to be used in most high-rise buildings. The issue of flame spread over a solid fuel is crucial since it relates to fire considerations in consumer products such as household furniture and building materials, and basic questions in combustion science. Nowadays, thermoplastic materials, which represent a high melt-flow fire spread risk, are widely used in construction industry. The flowing of thermoplastics’melt drips will accelerate the downward flame spread and fall down into the pool fire which appears at the foot of the wall fire. Large fire will be generated because of the wall fire and pool fire mutual enhancement mechanism. In this work, a new experimental setup is designed to quantitatively analyze the combustion characteristics of pool fires at different steady mass feeding rates. PP (Polypropylene), PE (Polyethylene) and PS (Polystyrene) thermoplastic polymers are selected as test materials and were heated into molten phase by electric furnace heater. N2 gas is continuously injected into the chamber to avoid a sudden ignition The characteristic parameters including dripping rate, flowing rate of hot molten liquids, burning rate and radiant flux of flowing pool fires are analyzed. The experiment results preliminarily suggest that the hot molten liquids induced by PP polymers are easier to drop and flow than that of PE and PS. Therefore, PP materials may be more dangerous for their faster pool fire flowing rate on the floor. Meanwhile, the burning rate of pool fires induced by PS is higher than PE and PP although the dripping rate and flowing rate of PS is the slowest since its large viscosity. As the mass feeding rate become larger, the dripping rate of three hot molten drips become faster. It also indicate the experimental phenomenon of surface tension flow, the flame front of pool fire does not concide with melt flow front except for PS at different mass feeding rate, the flame front of pool fire induced by molten PP or PE polymers is slower than the forward movement of the hot molten liquids. The reason for these combustion characteristics of molten thermoplastic polymers mentioned above may be related with viscosity and structures of thermoplastics, as well as the pyrolysis process of different thermoplastics.PU foam, as heat insulation material, has been widely employed due to its good energy saving properties. FPU (Flexible Polyurethane) and RPU (Rigid Polyurethane) are the two kinds most widely used PU materials, which FPU are more needed than RPU. However, the potential fire hazards of FPU larger than RPU subject to its melting-flow characteristic and structure transformation in combustion process. Therefore, it is necessary to conduct research on fire risk of Flexible PU foam. Downward-spreading flame over thermally thick flexible PU foam of various widths exposed to an external radiant heat source was studied in this work. The individual and combined influences of external radiation heat flux and width effect on the characteristic parameters, including the flame height, mass loss rate, flame spread rate and flame pulsation frequency were investigated. The experimental results show that the downward flame spread over flexible PU is an accelerated process under external radiation condition while the flame demonstrate steady state without external condition. As the flame spread over board, the amount of pyrolysis gases involved in the combustion process and showed a positive association with the external radiation heat flux. Compared with Rigid PU foam, the Flexible PU foam shows a more sufficiently combustion subject to its combustion characteristic and physical structure. The flame height is under a coupling effect of width and external radiation heat flux, while the flame pulsation frequency shows a negative correlation with the fuel width and the radiation heat flux. An approximation of linear pool fire was introduced to compare the burning behavior of FPU, which was validated by experimental data.RPU (rigid polyurethane) foam, as a heat insulation and thermosetted material, has been widely employed due to its lighter weight, greater convenience in modification, lower price and higher melting point compared to thermoplastic. On the other hand, it is found that in most fire scenarios, the materials which causing fire require external heating to enable flame spread. Therefore, the flame spread performance of RPU under simulated surrounding fire conditions must be taken into consideration. The downward flame spread is a complex process dependent on the important mechanisms for heat and mass transfer between a reacting and a non-reacting region. Downward-spreading flame over thermally thick RPU slabs of various widths exposed to an external radiant heat source was studied experimentally in this work. The influences of external radiation heat flux and width effect on the characteristic parameters, including the flame height, mass loss rate, flame spread rate and flame pulsation frequency were investigated. The experimental results show that the downward flame propagation accelerated process under external radiation condition, with the flame spread rate over RPU sample and the amount of pyrolysis gases involved in the combustion process being positively associated with the external radiation heat flux. When the external radiation heat flux reaches to a certain degree, the solid fuel is fully burnt out towards in the thickness direction. The flame height is under a combined effect of width and external radiation heat flux, while the flame pulsation frequency shows a negative correlation with the fuel width and a positive correlation with the radiation heat flux.