木荷林带阻火性研究

ON EFFECTIVENESS OF SCHIMA SUPERBA FUELBREAKING

采用锥型量热计和野外火烧试验方法研究木荷林带的阻火能力。锥型量热计采用75 kw/m2辐射强度、外部点燃条件下,测试木荷(Schima superba)与马尾松(Pinus massoniana)落叶的燃烧过程。结果表明,马尾松落叶的热释放速率峰值高(146 kW/m2),能量释放快。木荷落叶燃烧缓慢且释放热量少。野外火烧试验对室内试验结果进行了验证。火烧前后分别测定木荷林带和马尾松林的可燃物分布,试验火以地表火为主,蔓延速度为2.2 m/min,火线强度168-2 961 kw/m。有些地段由于可燃物较多,发生了树冠火,火焰高度达到8-8.5 m,火线强度达24,881-28 379 kw/m。火烧后林带受害不严重,无树木死亡。试验证明,木荷林带可以有效阻隔地表火和树冠火的蔓延,浓厚树冠层也可以阻挡短距离的飞火。

The present article aims at testing and analyzing the effectiveness of the shaded fire-breaking power through both laboratory experiments and those in the wild fields. As is known, Schima superba has been widely used in south China for shaded fuel-breaking. Experiments have been done in laboratory and wild fields for testing the effectiveness of the shaded fuelbreaking. The cone-shape calorimeter testing results indicate that the pine (Pinus massoniana) needles are easy to burn under the condition of the incident radiant site in a flux of 75 kW/m2 and the fire-ignition source. The peak value of the heat release rate of the pine needles usually appears earlier (22 s) and higher (146 kW/m2). The schima leaves usually burn slowly and has a lower total heat release. The mass loss curves that may result in usually indicate that the peak value of pine needle would be higher than that of schima leaves, which is 0. 14 g/s versus the schima 0. 08 g/s. A fire experiment has been done in the suburb of Guangzhou, which measures the fuel loads and their distribution in the stand of pine and fuelbreak before and after the fire experiment. There is almost no grass and litter on the ground of the fuelbreak due to clearing litter every year at the beginning of fire season. In the pine woods there are shrubs, grass groves and litters in the testing fields. During the burning experiment, most parts of the pine woods has been swept by the surface fire with the spread speed 2. 2 m/min and fire intensity 168-2 961 kW/m. But in some areas along the exterior fire testing area, some crown fire took place due to the high fuel load on the ground. The flame rose to 8-8. 5 m high with a fire intensity of 24 881-28 379 kW/m. Some trees' crown of the fuelbreak fell into flame due to the crown fire spreading. However, the flame failed to go over the fuelbreak, and neither took place spotting fire. Thus, the experiment results indicate that the fuel-break has any effect on the mitigating or diminishing of the fire intensity or stopping the fire spreading to any degree, which has proved that the shaded fuelbreak has the ability of fire resistance and its dense crown can block the spotting fire resources.