Thermal Decomposition Combustion And Fire Spread Characteristics Of Typical High-speed Train Interior Materials

In recent years,high-speed trains have become the most important route for people to travel.Once a fire accident occurs,serious casualties and environmental pollution will occur.Although the interior materials of high-speed trains are flame-retardant materials,which are difficult to ignite in normal environment,they can still be ignited under the action of electric fire or arson and even cause fire spread.Flame-retardant polycarbonate board as luggage rack and tray table and flame-retardant rubber floor cloth as an important part of the floor are the main interior materials of high-speed train.Their pyrolysis,combustion and fire spread characteristics are quite different from those of wood,non-carbonized polymers and carbonized EPDM,hence they are chosen as the main objects of this study.The pyrolysis,combustion and fire spread characteristics of samples in different environments were studied by experimental and theoretical methods,and corresponding models were established to facilitate fire hazard assessment.(1)Based on experimental methods to study the pyrolysis characteristics of samples from microcosmic and macroscopic perspectivesThe micro-pyrolysis characteristics of samples at different heating rates and ambient atmospheres are studied by TG-FTIR.The results show that the pyrolysis and mass loss curves of flame-retardant polycarbonate and rubber floor cloth move to the high temperature zone with the increase of heating rate.Kissinger method is used to calculate the activation energy of the samples.Flame-retardant polycarbonate mainly has a decomposition stage.The pyrolysis products of flame-retardant polycarbonate mainly include water,carbon dioxide,phenolic substances,methane,ethylene and aromatic ring organic substances in nitrogen atmosphere.The main functional groups are C-H,-CH3 or-CH2.There are two main stages in the pyrolysis of flame-retardant rubber floor cloth.The main pyrolysis products are water,carbon dioxide,methane and ethylene.The main functional groups are-CH3 or-CH2,C=C.The macro-pyrolysis behavior of samples was studied by means of fire propagation apparatus(FPA)under the nitrogen atmosphere with different the external radiation heat flux.Flame-retardant polycarbonate expands and foams during the whole pyrolysis process,and forms charring layer.Flame-retardant rubber floor will foam with the cracking of foam rupture.Under low external heat fluxes,the sample will break,while the external heat flux increases,this phenomenon gradually disappears.The relationship between mass loss rate and external radiation heat flux at nitrogen atmosphere was established to determine the latent heat of vaporization.(2)Based on experimental and theoretical methods to study combustion characteristics of samples under combined action of oxygen concentration and external radiation heat fluxFPA was used to study the combustion characteristics of samples in different atmospheres and external heat fluxes.The relationship between mass loss rate and external heat fluxes under different atmosphere was established,and the heat blockages under different atmosphere were obtained.The limiting oxygen concentration of samples under different heat fluxes was measured by oxygen-changing technology.When the minimum heat flux replaced the critical heat flux and the convective heat transfer coefficient of samples was a function of external heat flux,the calculated values by the ignition temperature model established were consistent with measured values.The relationship between ignition time and external heat flux under different oxygen concentration was established.It was found that the ignition time of expanded and foamed charring materials in different atmosphere was no longer strictly in accordance with the classical formula of thermal thin materials.The mass loss rate,heat release rate and CO and CO2 production rate of samples under different atmospheres and external heat fluxes were analyzed.There will be a distinct truansition zone in the combustion process,from oxygen control to external radiation heat flow control.(3)Based on experimental and theoretical methods to study flame spread characteristics of samples under combined action of oxygen concentration and external radiation heat fluxFPA was used to investigate the upward flame spread characteristics of samples under different atmospheres and external heat fluxes.The flame spread rate of the sample increases with the increase of oxygen concentration and external radiation heat flux,which obey the power exponential relationship.At the same external heat flux,the power exponent in the relationship between the flame spread rate and the mass fraction of oxygen at different oxygen concentration is about 2;at the same oxygen concentration,the minimum power exponent in relationship between the flame spread rate and external heat flux occurs at the 30%oxygen concentration;the relationship between the mass loss rate and the pyrolysis height of the sample is greatly affected by the type of the sample and obeys the power.For flame-retardant polycarbonate,the fitting index is mainly about 1.3 at low external heat flux and 2.5 at high external heat flux.For flame-retardant rubber floor cloth,the fitting index is mainly about 1.4 at low external heat flux and varies greatly at high external heat flux.For flame-retardant rubber floor cloth,the fitting index of mass loss rate and sample pyrolysis height fluctuates around 1 with different oxygen concentration and different external heat flux.The relationship between mass loss rate and flame height for flame retardant polycarbonate and rubber flooring cloth is basically in accordance with the"adherence theory",and there is a power relationship between them,with an index of about 2/3.The results of this study are beneficial to prevent high-speed train interior material fire,provide basic data and technical guidance for high-speed train fire safety design,and enrich the fire science theory to a certain extent.