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Knowing the risks: lightning

Direct lightning strikes on people are relatively rare, but can be extremely violent and often fatal. More common is a partial strike, either through induction from an adjacent or nearby conductor, or through the ground as the earth currents dissipate outwards. The actual power of the stroke is a combination of the current and the contact time.

Look out for mention of thunderstorms in the mountain weather forecasts when you are planning your hill trip, especially after a prolonged period of warm humid days. 

While out on the hill you will get a good warning of the potential build up of an electrical storm as they are usually accompanied by the formation of towering clouds which will start to develop as unstable air spirals upwards and condenses.

As a storm approaches, its location can be estimated by noting the difference in time between lightning flashes and the rumble of thunder. The light appears almost simultaneously, while sound travels at a speed of 1 km per 3 seconds. So, a six-second delay means that the storm is about two kilometres away.

Lightning strikes are quite frequent on summits and other projections such as pinnacles, because lightning takes the shortest route to earth. 

  • At the first sign of an approaching lightning storm, it would be advisable to move to a safer area

  • Scrambling terrain is particularly hazardous in lightning, and difficult to escape from quickly. A strike could easily knock somebody from his or her footing. Steep or exposed ground should therefore be avoided if storms are forecast, or at least be pre-empted by a very early start and finish. 

  • Retreat should definitely not be by abseil, because the wet rope provides an excellent conductor.

  • A projection such as a pinnacle acts as a lightning conductor that services an area with a radius corresponding approximately to its own height. This means that the area within this circumference is a relatively safe place to wait because the projection will deflect lightning strikes on itself.

  • Sheltering under an overhang or a tree is a hazardous course of action because a lightning strike will bridge the gap, taking the most economical route, in this case through the people and into the ground. 

  • It is much safer to sit out in the open wearing waterproofs.

  • A walking party sitting out a lightning storm should ideally crouch or sit upright on top of insulating material such as rucksacks and sleeping mats. Hands should be kept on knees rather than touching the ground. 

  • Metal items of equipment do not significantly increase the risk of attracting a strike, but if they start to hum and spark, it would be wise to accept the hint and lay them to one side until the storm passes.

The advice on this page is informed by the book 'Hillwalking', published by Mountain Leader Training UK, and reproduced with permission.