Wilderness and Rescue Medicine 8th Edition

Chapter 22: Lightning Injuries

Lightning is nature’s way of equalizing the dif- ference in electrostatic charge that develops between regions of the atmosphere and between the atmosphere and the earth’s surface during violent weather. Convection caused by ground heating, the advance of a cold front, or air pass- ing over hills and mountains tends to cause an accumulation of positive ions in the cloud tops, negatively charged electrons in the mid-level cloud, and a weak layer of positive charges in the cloud base. The more violent the convection is, the more rapidly the charges will develop and the more frequent the lightning. Cumulus clouds showing progressive vertical development indicate the potential for lightning. As the lower regions of a thunderstorm become more negatively charged, the earth’s surface below becomes more positively charged. The tendency of similarly charged objects to repel each other explains why your hair stands on end when you are about to be struck by lightning. Other signs of accumulating electrostatic charge include small rocks jumping about and the buzzing and glowing of the air around metal objects. A lightning strike occurs when these charges build up enough potential difference to overcome atmospheric resistance. A conductive column of ionized air is created by stepwise progressions of upward streamers, usually from a negatively

charged region, that ultimately meet shorter streamers from the opposite side. The connec- tion allows an electrical discharge generating mil- lions of volts and tens of thousands of amperes. Fortunately, about 95% of lightning passes from cloud to cloud, which means that only about 5% of lightning activity involves ground strikes. Lightning Injuries Despite its immense power, lightning is extremely brief in duration. The average discharge lasts for only about 0.001 seconds. This is not enough time for much of the electrical energy to overcome skin resistance and enter the body. Fewer than 20% of lightning victims die of their injuries. Most of the current passes over the skin surface on its way to the ground. As a result, the types of internal injuries typical of human-made electrical current are rarely seen with lightning. The energy in lightning dissipates in the form of heat and light. The instantaneous heating and expansion of the column of air through which the current passes generate the shock wave we hear as thunder. Like any explosion, if you are close enough, the shock wave can rupture ear drums, fracture bones, and damage internal organs. You can also be injured by flying rock, splinters, and other debris.