Study On China Fir Board Vertical Flame Spread And Suppression With Lateral Water Spray

Lining material is an important approach of flame spread while water spray is an effective way to control flame spread.China fir boards of four different thickness (10mm,12mm,15mm,18mm) were chosen to conduct the thermal gravimetric analysis experiments and Full scale experiments according with ISO9705 standard. The behavior of the china fir board vertical flame spread and its suppression with lateral water spray were studied.Moreover,the calculation method of lateral critical water flow rate was improved and was verified.The experiments were conducted to make the thermal gravimetric analysis of the china fir board from the microcosmic angel.The pyrolysis behavior of the china fir board and the changes of construction and ingredients of the material were studied using the TG-DTA analyzer.Considering the effect of heating rate on the prolysis process,according to the ISO TG curve key temperature representation,the pyrolysis characteristic temperature was determined to divide the preheat zone and prolysis zone.The infrared thermography was used to research the relation of china fir board vertical flame spread.By setting several equidistant scale marks with equal length in the real-time observation window of the infrared thermography,the time when the average temperature on every scale mark arise to the prolysis characteristic temperature was recorded to get the data of displacement of flame spread.Based on the data of displacement of flame spread the average velocity of flame spread was calculated.So the conclusion is:the vertical flame spread process of china fir board is divided into three stages:kindling stage,transition stage and developing stage.And the effect of thickness on the vertical flame spread was concluded.The method of curve fitting was selected to get the function of displacement of flame spread.Based on the relationship of velocity and displacement,the function of displacement of flame spread was differentiated to get the function of velocity of flame spread.The curves of the function of displacement of flame spread and the function of velocity of flame spread were plotted in matlab. The image processing method was introduced into the experiments.Flame height was acquired by the video frequency taken by the camera to give the parameters of lateral critical water flow rate.First,single frame image was processed by threshold segmentation and background noise reduction to extract the fire target;second,the height of the fire was calculated and calibrated;finally,to eliminate the errors of flame flutter,15 flames images in one second were chose to calculate the mean flame height.Full scale experiments were conducted according with ISO9705 standard to study the fire behavior of four china fir board of different thickness on the wall when the water spray acted on the preheat zone of the board,and the parameters such as heat release rate,board surface temperature and concentration of CO/CO₂ were measured.The bottom limit of the action area of the water spray was marked in the infrared thermography and the isothermal line(280℃～300℃) were set according to the pyrolysis characteristic temperature.When the isothermal line spread to the bottom limit the water spray started which acted on the preheat china fir board to the moment.If the pressure of the sprayer was adjusted to keep the isothermal line neither rising nor falling,it was the lateral critical water flow pressure of the preheat zone.So the experimental value of the lateral critical water flow rate could be calculated according to the jet characteristics of the sprayer.The calculation method of lateral critical water flow rate on the preheat zone of the china fir board was improved:The parameters such as fire height and heat release rate was modified;the criterion of preheat zone and prolysis zone was proposed;the thickness factor was added.The computation value of the lateral critical water flow rate of four china fir board with different thickness was calculated to compare with the experiment data.The result proved that the experimental data matched well with the model values.