一次“晴天霹雳”致死事件分析

Analysis of a lightning strike fatality

中文关键词:  雷灾事故  晴天霹雳  旁络闪击  跨步电压

英文关键词:Lightning disaster  Bolt from the blue  Side flash  Step voltage

中文摘要:

      对2017年广州从化地区一次"晴朗"天气下的闪电致死事件进行调查分析发现，这次事件是闪电首先击中一棵大树，然后击中附近人员头顶致死。根据目击者描述的时间和位置，利用闪电低频电场变化探测阵列的定位数据和广东电力等系统的雷电定位数据，结合广州番禺雷达观测资料，确定此事件是由一次含有7次回击的地闪过程的首次回击造成，其电流峰值强度为-30.9 kA。闪电起始于13.0 km高度的云内，经约600 ms云内发展过程后闪电通道从云体延伸出来，云砧区边缘（0 dBz）到回击点水平距离约300 m，降水区边缘（18 dBz）到回击点水平距离约1.8 km。使用雷击现场等效电路模型，计算旁络闪击空气击穿场强可击穿空气与人头部连接为通路，根据电路分流原理，如果雷电流击中13 m高的大树后流经到"跳点"（树干上方1/4）处后，则有13.2 kA雷电流直接闪击到受害者身上，同时还承受了78.3 kV跨步电压伤害，而距离雷击点10 m远的目击者仅承受1.3 kV跨步电压。

英文摘要:

      This study investigate and analyze a lightning strike fatality occurred in a sunny day in Conghua of Guangzhou in 2017. The lightning first hit a big tree, and then hit the head of a nearby person and killed him immediately. According to the occurrence time and location of the incident described by witnesses, and using the location data of Low Frequency Electric Field Detection Array (LFEDA) and Guangdong Lightning Location System (GDLLS) location data as well as Radar data from Guangzhou CINRAD-SA radar, the incident is identified as one lightning strike fatality caused by a "bolt from the blue". The accident discharge is found to be the first Return-Stroke (RS) with the current peak of -30.9 kA, which belonged to a Cloud-Ground (CG) lightning flash with 7 RSs. The flash initiated at an elevation of about 13 km. After the cloud development process of about 600 ms, the lightning channel extended outward from the cloud. The horizontal distance from the edge of the cloud anvil (0 dBz) to the return point is about 0.3 km, and the horizontal distance from the edge of the precipitation area (18 dBz) to the return point is about 1.8 km. According to the equivalent circuit model of lightning strike, we calculated the air breakdown voltage of side flash and found that the "jump point" between 1/3 and 1/4 above the trunk could form conductive path to the head of the victim. This paper assumes that the "jump point" is at 1/4 above the 13 m height trunk. Based on the Circuit Shunt Principle, the process of the incident can be inferred to as:The flash hit the tree and the current flowed to the "jump point", then, the 13.2 kA lightning current blinked directly to the victim and the victim also experienced the injury of 78.3 kV, while the witness who was 10 m from the lightning strike point only experienced 1.3 kV step voltage.