Experimental Studies On The Effects Of Spacing On Vertical Flame Spread And Dripping Behavior Over Thermally Thin PMMA

With the global scientific/technological progress and the rapid development of urbanization,thermally thin polymer materials are increasingly used in housing decoration,including large entertainment mall decoration supplies and all types of billboards.Thermally thin polymer materials are also used in public gathering places.Once ignited the thermally thin polymer materials,characteristics of high heat and rapid combustion,will increase the fire load,the fire flame will quickly spread to neighboring areas to form a large area of a three-dimensional fire.The burning of polymer materials will produce a large number of toxic and harmful gases,destroying life and propety.Most of the previously published studies dealing with fire spreading behavior of thermally thin materials are based on medium-sized material suspension combustion or wall burning.However,the qualitative and quantitative analysis of the limited conditions of space distance between the material and the wall are still not yet investigated.The combustion of polymer materials during the fire to the state of melting and dripping raised questions about the ability of these materials to limit the spread of fire.In this study,the most widely used thin-type polymethyl methacrylate(PMMA)was thus employed to examine the fire spread and dripping behaviors of the material by changing the space distance between PMMA and the wall.Thermogravimetry analyses(TGA)were first used to measure the pyrolysis characteristics of PMMA materials in an effort to determine the basic parameters for the follow-up material fire propagation.A cone calorimeter was then utilized to measure the PMMA combustion performance to analyze the impact of different radiation intensities on the fire parameters,such as ignition time of the material,heat release rate,and effective heat of PMMA with different thicknesses.Afterward,self-built thin material vertical fire spread combustion and dripping behavioral combustion testing platforms were employed to evaluate the upward flame spread,downward flame spread,and dripping behavior of thermally thin PMMA sheets.Also,experiments were performed to study the effect of spacing between the wall and thin fuels on the upward flame spread.Uniform PMMA samples of 1 mm thickness were utilized for that purpose.The results suggested that as the spacing between the wall and thin fuels increased,the front flame height,back flame height,pyrolysis height and burnout length followed similar trajectories.First,they showed an increasing trend followed by a decrease.The maximum trajectory was observed at a spacing of 13 mm,where the trajectory curve reached a maximum value.The length of the pyrolysis region was gradually stabilized as the fire propagation rose.The pyrolysis velocity and the burnout velocity were also theoretically verified,and mathematical models representing the change in heat flux on the back surface was presented.In the contrast upward flame spread experiments,similar experimental platforms with a 1 mm thick PMMA plate were used to evaluate the effect of the distance between the material and the wall on the downward flame spread.The results indicated that by increasing the space distance,the flame height,the pyrolysis length,and mass loss rate values first increased then decreased.The mass loss rate showed a linear relationship with the pyrolysis length.Comparison between the flame spread rates of PMMA sheets of different widths revealed that the influence of the width of the model on the downward flame propagation characteristics of the thin PMMA sheet could be neglected.It was found that the flame radiation reflected from the wall could affect the heat of the preheating region temperature,which was first increased and then decreased.The dripping behaviors of vertical burning thermally thin PMMA with different spacings parallel to the wall were examined using a UL94 experimental study using a small scale combustion of the polymer.It was found that by increasing the spatial distance,the dripping time,dripping mass and burnout growth distance first decline then followed by a rose.The mechanical equilibrium equation between gravity,material viscous force and melt strength was evaluated.It was demonstrated that the dripping behavior of PMMA board followed the large size dripping behavior.This conclusion was reached by assuming that the dripping behavior was related to the net heat flow of the material,the material tensile viscosity,and mass of the PMMA melt.