Home Hiking hints Health & safety Lightning strikes
Caught in a storm ...
Though not one of the principal perils of hiking, lightning has caused a number of serious, and most avoidable, accidents. The very nature of this pastime places hikers on or near the most frequent targets, peaks and ridges help produce the vertical updrafts and rain cloud conditions which generate lightning, the prominences serve to trigger the strokes. Hikers therefore should understand the basic mechanisms involved and fix their minds to the fundamentals of evasive action.
For all practical purposes the hazards are three:
- a direct strike,
- ground currents, and
- induced currents in the immediate vicinity of a strike.
Electrical potential builds up in a cloud in somewhat the same manner one’s body picks up an electrical charge on a dry day. Air is normally a very poor conductor (good insulator) of electricity; trees, rocks or earth are better conductors, more so when wet; the human body is still better; and most metals are best of all. Lightning seeks the path of least total resistance between the cloud and earth – the shortest possible line through the air. Ordinarily the closest ground point is directly below the cloud, but a summit off to one side can be closer and become the bull’s eye.
Air ceases to be a good insulator when subjected to a sufficiently high electrical pressure; it ionizes and thereupon loses its insulating quality and becomes a conductor. The ionizing breakdown around a conducting projection often gives off a crackling noise caused by small sparks. The distinctive odor of ozone is usually noted. A bluish glow or corona (St. Elmo’s fire) may be seen. If a person’s head is the projection, the hair (if any) crackles and stands on end. Corona discharges have often been observed with the nearest cloud seemed too far away to be at all relevant. The sound or sight of corona does not necessarily indicate danger, but lacking more precise indication should be regarded as a warning, especially when thunderclouds are nearby. Additionally, any atmospheric activity symptomatic of commotion should stir suspicion. A sudden rush of cold air perhaps announces a strong cold front with possible lightning. A cloudburst of enormous raindrops or monster snowflakes or huge hailstones almost certainly means a cumulonimbus is overhead.
Lightning is, of course, electricity, which is a stream of electrons. When the more than 100 billion billion electrons in an average bolt strike a peak or a tree, they do not just lie there in a puddle, but immediately spread out in all directions. In the process, considerable damage can result. Two factors determine the extent of human injury; the quantity of current and the part of the body affected.
The worst threat is the passage of electricity through the body in a way which impairs some vital function such as heart, brain or breathing action. A current from one hand to the other through the heart and lungs or from head to foot through virtually all organs, is most dangerous, even if relatively small; one can survive a larger current from one foot to the other through the legs.
Hikers face potential hazards: large currents can cause deep burns at points of entry and exit; a mild shock may momentarily startle them or set off muscular spasms, or they may move about in semi-consciousness.
First thought should be given to avoiding areas which might be hit. The governing rule is to seek a location with nearby projections or masses which are somewhat closer than one’s own head to any clouds which may drift by. In a forest, the safest shelter is amid the shorter trees. The middle of a ridge is preferable to the ends: avoid shoulders.
An electrical discharge at a strike point instantly radiates outward and downward, with the intensity of a flow, and consequently the danger to hikers, decreasing rapidly as the distance from the strike increases. On firm rock, especially when wet, the major path in most cases, is along the surface. Lichen patches, cracks, or soil may hold moisture and thus provide easy paths. High-voltage currents tend to jump across short gaps, as in a spark plug, rather than take a longer path around.
Current flows because of a voltage difference between two points along its path. A person bridging two such points, with some part of his body, presents a second and probably better path for the current, some portion of which is therefore diverted through the body. The wider the span the greater is the voltage difference and the greater the flow through the body.
With this background, several precepts can be listed:
- Avoid moist areas, including crevices and gullies.
- Span as small a distance (occupy as little area) as possible. Keep the feet close together; keep the hands off the ground.
- Sit, crouch or stand on insulating objects, if possible – a pullover or sleeping bag, preferably dry.
- Stay out of small depressions; choose instead a narrow slight rise. A small detached rock on a scree slope is excellent.
- Stay away from overhangs and out of small case. Large caves are very good if one keeps clear of the walls and entrance. However, a cave might well be the lower terminus of a drainage crevice and in such case, should be avoided.
- When on a ledge, crouch at the outer edge, at least 1m from the rock wall, if possible.
- Contrary to popular belief, metal objects do not attract lightning as such. However, in the immediate vicinity of a strike, metals in contact with one’s person may augment the hazard from induced currents, the nature and mechanism of which lie beyond the limits of the present discussion. Induced currents usually are quite small, but when added to ground currents may mean the difference between life and death. Thus, it is best to set aside all metals, but to keep them close by (don’t worry about articles buried in the pack). A metal pack frame might well be positioned to provide a more attractive path for ground currents besides the past one’s body. At distances greater than 50m from a possible strike, there is no need to divest oneself of metal objects.