Study On The Combustion Characteristics Of Underground Fire Of Larix Gmelinii Plantation In Daxing'an Mountains

Forest underground fire is a kind of forest fire which occurs in humus and peat layer.Forest underground fires account for only 1% of the total forest fires,but go with great damage to the forest.Forest underground fire has challenged the fighters for a long time because of the difficult to be monitored and fighted.There are great difficulties in the process of monitoring and fighting the "invisible and untouchable" forest fire.The Daxing'an Mountain is the frequent occurrence area of forest underground fire in China.In this paper,the typical vegetation Larix gmelinii Plantation in Daxing'an Mountain was taken as the research object,and the combustion characteristics of forest underground fire were studied through the indoor control simulation combustion experiment,correlation analysis,regression analysis,variance analysis and other methods.And the targeted and practical underground fire monitoring and fighting countermeasures were put forward.The main research results are as follows:(1)Through the control combustion experiment,it is found that there is no flame and spark in the whole process of forest underground fire combustion,and the humus after burning is brick-red.According to the content of organic matter before and after combustion,the underground fire in tatoudianzi and water wetland was fully burnt.In the vertical burning experiment of underground fire,the highest temperature increases with the increase of depth,in which the humus burning temperature of tatoudianzi is the highest.There are significant differences in the highest temperature of vertical combustion with different land classification and humus plasmid diameters(P< 0.05).(2)Because of the influence of oxygen content in the combustibles,the humus plasmids with the diameter ? 20 mesh and ? 40 mesh spread fastest than other diameters in all land classifications.The humus plasmids with the diameter?20 mesh,?40 mesh and ?80 mesh spread fast under agricultural land conditions,and the vertical spread speed is the fastest and3.45cm/h when the humic plasmid diameter is ?40 mesh.(3)In the process of horizontal combustion of underground fire,the combustion temperature of near surface layer fluctuates greatly,while the highest temperature of horizontal combustion of deep humus is positively correlated with the horizontal distance.Under sameland classification,the influence of different humus plasmid diameters and depths on the highest temperature of horizontal combustion is significantly different(P< 0.05).There are also significant differences in the highest temperature of flat combustion with different land classification and humus plasmid diameters under the same depth(P< 0.05).(4)The spreading speed of humus in sloping mountains,water wetland,flat mountains and agricultural land is slower in the near surface layer,faster in the deep layer,and there is a positive correlation between the spreading speed and the depth.The spreading speed of humus in tatoudianzi is faster in the near surface layer than in the deep layer.The spreading speed of horizontal combustion of underground fire is only affected by the land classification,and there is a significant difference(P<0.05).(5)The change of surface temperature is caused by underground fire,so monitoring surface temperature is an important means of monitoring underground fire.When the humus burning depth of sloping mountains is greater than 19.87 cm,or humus burning time of tatoudianzi is greater than 16.90 h,the surface temperature will be the same as room temperature.When the humus burning depth of flat mountains is 36.06 cm and the humus burning time is28.05 h,the change of surface temperature can still be caused.(6)For the monitoring and fighting of forest underground fire,we must implement the principle of “early,small,complete”.Once the monitoring of underground fire is delayed,it will be extremely difficult,and fighting risk factor will also increase.Digging fire-proof ditch is the main method of fighting underground fire.The depth of the ditch is 0.5-2m or the peat or humus layer is excavated until the mineral soil layer appears.At the same time,we must prepare for the tough and protracted battle,prevent reigniting,and pay more attention to the safety protection of firefighters.