Wilderness and Rescue Medicine 8th Edition

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Section V: Environmental Medicine

General Principles

General Principles

Useful Information • Isolation and height determine the likelihood of being struck. • Enclosed, grounded structures or vehicles are protective (surface effect). • Ground current is the most common source of injury. • Metal and water can conduct current great distances. • Leader strokes travel about 30 – 50 meters. 5 *

Risk Management • Sit on an insulator to reduce contact with ground current • Spread your group out to avoid a multiple casualty strike • Inside a vehicle is best, on or under a vehicle is bad. • If moving toward safety; keep moving • Don’t lean on a wire fence • Lower is safer

© 2018 WMA

© 2018 WMA

Because lightning can travel considerable dis- tance, you should evacuate hazardous areas as soon as thunder is heard, or lightning is seen. The rapid development of cumulonimbus clouds is an early warning, although orographic convection (air passing over high terrain) can cause lightning from a clear sky in dry climates. Lightning also can strike during snowfall in higher elevations. Risk Versus Benefit Although there are ways to reduce the probability of being struck by lightning, as indicated in this chapter, there is no truly safe place during a thun- derstorm. The physics of lightning have, so far, defied complete understanding and predictability. Fortunately, the overall probability of being struck is low, even if you do everything wrong. Some lightning myths have been successfully debunked. For example, the fear that carrying met- al objects or using a cell phone attracts lightning has been proven to be unfounded. Your trekking pole or ice axe will not increase your probability of being struck unless you pack it so that it proj- ects above your head, making you taller. Devices marketed as lightning repellents or ion diffusers to reduce strikes do not work and will actually increase the probability of a strike if they project above the masthead or building. Unfortunately, the incidence of side flash renders the “cone of protection” concept unreliable for humans seek- ing shelter near tall trees or structures.

For raft guides, the perennial question is wheth- er to stay in the raft on the river or to go ashore. Going ashore makes you higher, but if it allows for a large crew to spread out it might be worth it. If you choose to stay on the river, being close to the bank may reduce your isolation. There are few options for boats on open water. The only way to reduce your probability of being struck is to reduce the time of exposure. If the storm cannot be avoided, at least set a course to take you clear of the storm as quickly as possible.