The Danger of Lightning

Advice on Staying Safe

The recent tragic death of a hillwalker who was struck by lightning near a summit in the Southern Highlands has served as a reminder that, even though the chances of being struck by lightning are small, high on a mountain is a dangerous place to be during a storm. The advice below is taken from the book 'Hillwalking', published by Mountain Leader Training UK, and reproduced with their permission.

Lightning strikes rarely come as a 'bolt out of the blue'. Towering clouds build up as unstable air spirals upwards and condenses, giving a good warning to the observant walker. 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. A six-second delay therefore 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. These are the areas of greatest risk, and at the first sign of an approaching lightning storm, the party should evacuate 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. Retreat should definitely not be by abseil, because the wet rope provides an excellent conductor. 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.

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.

A projection such as a pinnacle or post 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.