Fundamental Study of Wood Ignition Medchanism under High Voltage and Large Current Discharge Condition for Development of Control Method of Forest Fire

众所周知，闪电确实会点燃森林，尽管我们不知道闪电是如何点燃森林的细节，森林的哪些部分是森林火灾的始作俑者。我们也不知道森林火灾中由小火到大火的发展过程，也不知道闪电如何产生点火能量。为了确定阿拉斯加森林中闪电痕迹的存在，并阐明闪电引起火灾的特征，我们在阿拉斯加进行了实地研究。它们大约占15%，这表明在北方森林中有可燃材料或燃料。2.北方森林中的燃料包括黑云杉的嫩枝和针叶，覆盖地面的苔藓厚度约为10厘米，树枝和森林地面上的地衣。在通常的森林火灾条件下，树干和粗树枝不会燃烧。3.对这些燃料分布测量的重力测量表明，阿拉斯加北部森林火灾产生的最大（理想）热量为72.4MJ/m^2。当假设树的平均高度为6.4m时，这变为每米树11.3MJ/m^3。电压发生器（1Gs）用于进行冲击电压测试。关西技术的1.2MV 1G主要用于进行基础实验，以评估放电对树木的损害，代表闪电，以及引发火灾的条件。CRIEPI的12 MV 1G被用来验证标准雷电脉冲电流是否会引起干草着火。用摄像机拍摄的两个爆炸现象将用Uman和Voshall（1968）得到的理论结果来解释。最后，结合野外调查和实验结果，提出了森林雷击着火机理，并进行了理论思考。

It is well known that lightning does ignite forests, although we do not know details of how lightning ignites forests, what parts of a forest act as the starter of forest fires. We also do not know the growth processes from small to large flames in a forest fire, or how lightning produces the energy for ignition.Field research in Alaska was carried out to establish the existence lightning scars in forests there, and to elucidate the characteristics of lightning-caused fires Results of the field research in Alaska may be summarized as follows :1.Ignition probabilities are not small in boreal forests near Fairbanks, Alaska. They are around 15 % that suggests that there are flammable materials or fuels available in the boreal forest.2.Fuel in this boreal forests includes twigs wish needles of black spruce, moss which covers the ground at a thickness of about 10cm, and lichen on branches and forest floor. The trunks of trees and thick branches do not burn under usual forest fire conditions.3.Gravimetry of distribution measurements of these fuels shows that the maximum (ideal) heat generated by boreal forest fires in Alaska would be 72.4MJ/m^2. This becomes 11.3MJ/m^3 per meter of tree, when an average height of 6.4m is assumed.The voltage generators (1Gs) were used to carry out impulse voltage tests. The 1.2MV 1G of Kansai Tech was mainly used to carry out basic experiments to evaluate the damage to trees due to discharges, representing lightning, and the conditions causing fire ignition. The 12MV 1G of CRIEPI was used to verify whether standard lightning-impulse currents cause ignition in dry grass. Two explosive phenomena taken by a video camera will be explained by using theoretical results obtained by Uman and Voshall (1968). Finally, a forest ignition mechanism by lightning based on the field research and experimental results, and theoretical consideration was obtained.