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

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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.