Lightning Hazards to Mountaineers
Alvin E. Peterson*
Although statistics show that lightning is not one of the major hazards of mountaineering, enough casualties and near casualties have been reported that the matter is at least one of concern. Mountain climbers often find themselves on prominent peaks and exposed ridges, which are particularly subject to lightning strokes and lesser electrical discharges. There are two reasons for this: (1) the ridges help produce the vertical updrafts and the rain-cloud conditions which generate lightning, and (2) the prominences serve to trigger the strokes. There are protective measures that can be taken by the climber, and these should be more generally known.
Causes and Nature of Lightning
The lightning process is much the same as that in which a person’s body picks up a charge on a very dry day. Scuffing the feet across a carpet results in a separation of positive and negative charges; these are always present but ordinarily neutralize each other in pairs. The positive charges remain behind on the carpet; the body is left with a surplus of negative charges which may result in a potential difference of several thousand volts with respect to a nearby uncharged object such as a water pipe or another person. Bringing the finger close enough to the uncharged body results in a spark, with attendant flow of current, and a mild shock.
Natural lightning is similarly caused by separation of charges, this time between parts of a cloud and between cloud and earth. There has been much study of how the generation of charges and their gross separation are brought about, but the exact process still remains in doubt.(1,2,5)** The separation apparently is caused by the action of vertical updrafts on raindrops; the freezing of water can produce charge separation, and this probably plays a part. By whatever mechanism, parts of the cloud take on large potential differences (voltages) with respect to other parts of the cloud and to the earth.
The updrafts that appear necessary to generate an electrical storm are usually of thermal origin. Most commonly they are produced by unequal solar heating of adjacent parts of a landscape; variations in reflection and absorption because of soil, rock or vegetation, the presence of lakes or snowfields, or cloud shadows can cause such zones of unequal heating. Storms so produced are of the heat or convective type. Frontal storms are so-called because they are generated at the moving edge of either a warm or cold front.(5)
A storm generated by a mountain slope is sometimes called an orographic or mountain storm. A slope will push upward a horizontally moving air mass such as a warm front. Also, surface differences in soil, rock, vegetation cover, and snow patches may be quite marked on a mountain side and these, as mentioned above, can produce thermal updrafts and attendant lightning.
Whether or not a lightning stroke takes place between cloud and ground depends on whether or not a high enough voltage gradient exists to cause progressive breakdown or ionization of an air path between cloud and ground. Air is ordinarily a good insulator; subjecting it to a strong enough electrical stress or local voltage gradient causes it to "ionize” and become, in effect, a conductor. In other words, an electrical current will begin to flow between cloud and earth if the air is subjected to a high enough voltage difference, or stress, per unit length of air path. The gradient required to initiate breakdown in air near a charged body is about 30,000 volts per centimeter. Over a long path such as that of a lightning stroke the average gradient which would afterwards cause breakdown to propagate is probably about 5000 volts per centimeter.
If a sharp conducting point projects from the ground surface toward the charged cloud, the electrical stress is concentrated around the point at the expense of the flatter surfaces nearby. Such a point, therefore, promotes ionization or breakdown of the air about it and to some extent encourages the formation of a lightning stroke to it. This is the idea of the projecting "air terminal” of a lightning rod, which is intended to receive a stroke that would otherwise strike the roof. A prominent peak or an exposed ridge will act as such a point. A mountaineer standing exposed on such a peak or ridge may similarly receive a stroke. It also follows that if the mountaineer is near (but not too near) and well below such a projection, he will have considerable protection against being hit by a direct stroke; the preferred path for the stroke will be to the higher point; his chief hazard will then be from ground currents, discussed below.
The extent of the zone protected from direct strokes (see Fig. 1) may be inferred from experience with lightning rods.(5)* The top of the cliff or other prominence should have a height at least five or ten times one’s height. One should not be closer to the vertical cliff, horizontally, than at least one’s own length—preferably farther; when too close, the body may become an alternate path for the stroke. Likewise, one should avoid being under an overhang: this may act as a "spark gap,” and the shortest path for the stroke may well be from the edge of the overhang down through one’s body (Fig. 2). With the above as a guide for the closest distance, the safe zone then extends out to a distance about equal to the height of the local prominence above one. Thus, beneath a cliff 50 feet high, one is fairly safe from direct stroke if one is more than 5 feet and less than 50 feet from the cliff wall. The further need to protect from ground currents is discussed below.
The highest point on a landscape is generally the most likely to initiate a stroke, but this is not always true. Much depends on where the charged part of a cloud is located with respect to prominences on the ground. A cloud with its attendant charges might be well below a summit, so some minor projection on the side of the mountain could trigger the stroke to it. The terminal point of a ridge leading away from a higher peak could easily initiate a stroke to it(3) (Fig. 3).
Under some conditions it is quite possible that the initial point discharge may drain off the charges as rapidly as they are formed and so may actually prevent the formation of a lightning stroke. This cannot be predicted. If one is personally concerned, he should not rely on this taking place.
The local breakdown of the overstressed air about a projection gives off a crackling noise due to small spark streamers. If it is dark enough, a bluish glow may be seen. In sunlight the noise may be the only evidence. It is the repetitious noise that is heard when combing one’s hair with a rubber comb on a very dry day. Engineers give the name "corona” or "corona discharge” to this glow; navigators often use the more poetical name "St. Elmo’s Fire.” If a person’s head is the projection referred to,— and it still possesses hair,—the hair will crackle and stand on end.
The writer and others have noted such corona discharges on peaks when the nearest thunderclouds seemed too far away to have any local effects. The near vicinity may even have been in bright sunshine. Possibly the atmospheric charges in these cases were left by thunderclouds that had been in the vicinity but had evaporated, leaving their electrical charges isolated on the air molecules.
The sound or sight of nearby corona does not necessarily indicate hazard but lacking a more precise indication, it should be regarded as a danger sign. This is especially true if there are nearby thunderclouds.
Nature of Personal Hazards
Two things govern the injury done to the body by the lightning electricity: the quantity of electricity and the part of the body affected.
Electrical quantity is proportional to the amount of current and the time during which it flows. Unlike contact with a power line, exposure to a lightning stroke lasts only a few thousandths or millionths of a second. Several amperes may pass through the body in such a short time and do no more damage than a few hundredths of an ampere when in contact with a power line.(13) The term "current” is used in this paper because it is a term best understood by the average reader. Its time of duration is as important as its amount, but this is a factor not under one’s control.
The basic hazard in electrical exposure lies in the passage of electricity through the body in a way to impair some vital function such as heart action or breathing. A current through a muscle causes muscular spasms or involuntary contractions; with the heart muscle it may cause stoppage or a destruction of the natural rhythm. A current through the brain, spinal column or other nerve center may block its functioning and cause unconsciousness or stoppage of breathing. If currents are large enough and last long enough, they can cause deep burns and tissue damage.
It is obvious that where the current flows in the body has much to do with its damage. A relatively small current through a vital spot,—as from hand to hand through the heart, or from head to foot through brain, spine or heart is most dangerous. One could survive a larger current from foot to foot through the legs, from shoulder to hand, or from feet to pelvis; here the heart, brain and spine are not involved, or are involved to a lesser extent.
The mountain climber in an exposed place may encounter an additional hazard: a mild shock, not too serious in another place may, merely by startling him or by causing him to lose muscular control for just an instant, throw him off balance and cause a serious fall. Likewise a person may move about while unconscious, or in the twilight zone of returning consciousness, and so fall off the cliff.
Ways in which electrical currents may be caused to pass through the body are as follows: 1. By a direct stroke. This is most likely to happen if the person is on or near the top of a peak or ridge or out in a flat open space. He may act as a lightning rod terminal to initiate the stroke. Such a stroke would nearly always be fatal. 2. By electromagnetic induction. The body is a fairly good conductor and if very close to the path of the main stroke, circulating or "eddy” currents will be set up in it by magnetic induction.(6) Distances involved are within a few feet of the main current path, so usually one cannot disassociate this from the direct stroke. 3. By electrostatic induction. A lightning stroke redistributes the voltage gradients in its vicinity; nearby objects, though not in the path of the stroke, must take on new charges in keeping with the changed conditions. Another way of saying this is that the body has a certain capacitance with respect to the cloud and the earth; the voltage changes due to the stroke cause capacitance currents to flow, bringing the body to the new potential or voltage. Such currents are usually small. They may manifest themselves by a stinging sensation in the soles of the feet or other points of contact. 4. Through earth currents caused by a nearby stroke. This aspect of lightning is the one the mountaineer is most likely to encounter. It is the one against which he can most readily take precautions, and an understanding of it is helpful. (For an excellent survey of this subject the writer recommends citation (3), which relates to the well-known "Bugaboo Accident.”)
A lightning discharge between cloud and earth is usually triggered by a preliminary small pilot stroke; this is followed by one or several heavy current components, each passing a current with a peak value of as much as 100,000 amperes; each component may last only 1/10,000 of a second or less. Lower values of current (50 to 1000 amperes) follow the same discharge path during the intervals between the large components. The whole discharge occasionally lasts as long as several tenths of a second. On striking a projecting rock this current seeks the easiest ways through or over the rock and into the surrounding landscape. The "easiest” path is that one having the lowest electrical impedance, or combination of resistance and inductance; this path may not be readily apparent by inspection. On firm rock, especially when wet, the path of lowest impedance will in most cases be over the surface and downward. There will be a tendency for the discharge to jump across short gaps rather than go around them by way of the longer surface path (Fig. 4). Lichen patches, or cracks in the rock that hold moisture, mineral salts, soil and plant roots may give lower impedance paths that most of the current will follow (Fig. 5).
The flow of current over the rock surface, or through a wet fissure near the surface, means that there is a voltage difference between two adjacent points on such a surface. (The term "voltage gradient” expresses the voltage per unit length of path.) A person bridging two such points with some part of his body will present a second, and often better, path for the current, and so some part of the current will pass through his body. This might be only a minute fraction of the main stroke. How much current goes through the body depends on several things, such as (a) the amount of current over the rock, (b) the impedance of the rock path compared to the body path, (c) one’s insulation from the rock due to the skin, gloves, clothing or other material, and (d) on the spacing between points of bodily contact. With regard to spacing, the farther apart the points of bodily contact, in the direction of the current, the larger will be the potential or voltage available to put current through the body.
The human body, it may be noted, has an electrical resistance of the order of 100,000 ohms from hand to hand when the skin is dry; when wet and salty this reduces to 5000 ohms or lower. Much of the body’s resistance thus lies in the surface of the skin. The figures also indicate that one is relatively safer from earth currents when dry than when wet. In the short time duration of a lightning stroke the body may recover from momentary currents amounting to a hundred amperes or more.(13)
The hazard from earth currents decreases greatly as one gets farther away from the prominence that was struck (Fig. 3). Likewise, a broad peak presents less danger than does a sharp spire. To illustrate: assume the rock surface to be uniform and that there are no wet fissures to divert the current. Then, near the top of the peak, because of the smaller circumference, the current is squeezed into a narrower path than it is farther down; so the current density and voltage gradient are correspondingly higher. Thus, a person 500 feet down from the peak would be exposed to gradients only one-tenth as large as if he were 50 feet below the peak. (Much closer than 50 feet, the chance of being involved in a direct stroke becomes increasingly great.) By the same reasoning, a very sharp spire presents greater hazards due to ground currents than does a broader peak.
Types of Lightning Accidents
Perusal of reports indicate that mountain lightning accidents may be classified into three groups by location, as follows. Illustrative citations are noted.
1. Peak accidents.(7,8,10) In these, the climbers were on top of the actual peak when the lightning struck. The writer believes that in the cited cases they were exposed to some fraction of the main stroke and not the entire stroke. The victims were knocked unconscious or paralyzed and suffered severe burns. Clothing was ripped in one case. In two of the accidents added injuries from falls were reported.
2. Accidents just below peaks.(3,4,11) These cases appear to have involved only shocks and injury due to earth currents. Again, unconsciousness, severe burns, spasms and further injury from falls were reported.
3. Accidents in relatively flat places.(9) The cited case occurred in a fairly flat area below a saddle. The two persons immediately killed had taken refuge under a rock overhang and received a discharge from the lip of the overhang. Lightning struck 50 feet away. The third person, ten feet from the rock, received shock and burns from earth currents; he walked away but later died. This situation is similar to the common one in which lightning strikes a golf course and the victims take refuge under a tall tree or in an unprotected small building.
1 The most obvious way of avoiding lightning in the mountains is not to be on exposed peaks or ridges, or in an unprotected flat expanse, during an electrical storm. If such a storm can be predicted, it is sensible not to climb.
2. If you are caught in an exposed place, and you have some time before the storm reaches it, you should get as far down the mountain and away from the exposed ridges as you can (Fig. 3). Especially avoid those that dominate the skyline. The middle is preferable to the end of a ridge. A lower scree slope, with a seat on a small discontinuous rock (Fig. 6), is very good; you should not, however, be the high point in a flat plane, as noted below. Avoid being under prominent or isolated trees.
3. If strokes seem imminent, or are striking nearby, seek at once for a place that will protect you from direct strokes and from ground currents. Waste no time. A flat shelf, a slope or a slightly raised place dominated by a nearby high point would give protection from direct strokes (Figs. 1 and 3). The space should allow you to crouch at least four feet, preferably more, from any vertical rock; the rock above you should be at least five to ten times your crouched height; you should be no further out from the base of the prominence than its height above you. You should be well down from the top of any sharp spire,—say 50 feet as a minimum, preferably much more. If there is any choice, select a spot on dry, clean rock in preference to damp or lichen-covered rock. A scree slope, as noted above, should be very good. Keep away from an earth-filled or damp crevice that leads upward. Avoid taking shelter in a crevice or cave(3,12) unless it is quite large and high: it should allow you to sit four feet or more from any vertical walls, and there should preferably be ten feet or more above your head (Fig. 7). A cave might well be the lower terminus of a drainage crevice leading upward, and such a one should be avoided. Also do not sit close to the cave entrance, thereby avoiding surface currents tending to bridge the opening. Where lightning is involved, a small cave or protective overhang conveys a false sense of security. Avoid sitting in a shallow depression or hole (Fig. 4) whose sides are closer to you than four or five feet; in such a place the charge may well jump across the opening and so enter your body.(10) (This is again the "spark gap” situation.)
4. A crouched position, or a seated one with the knees drawn up and feet close together, seems best (Figs. 2 and 6). The smaller the distance spanned by your contact points with rock or ground, the better off you are. Especially avoid having two contact points so that head or torso is included between them. For instance, do not stand or sit with hand, shoulder or head touching a surface.
5. You should use any insulating material you might have to sit on (Fig. 1) and insulate yourself from the rock or ground surface. A coil of nylon rope is an excellent insulator when dry and even a fairly good one when wet. Other things which might be used are: a wooden pack-board, rubber soled shoes (preferably without nails), a poncho folded several times, a rubberized rain jacket, a folded sleeping bag, a pack, a folded woolen shirt. Dry items are always better than wet ones; if it is raining, a poncho might well be used to keep one’s clothing and skin dry. A metal pack frame, laid flat on the ground, should be good if you can sit on it within its compass: ground currents would follow the metal frame in preference to one’s body. Sitting on a small, flat, loose rock,—one large enough to keep your feet on as well,—is also good; it should be a piece lying loose on the main body of rock or earth; such a seat, in the middle of a broken scree slope, should be good.
6. If you are caught on a cliff where you may fall off if you lose consciousness or suffer muscular spasms, you should tie yourself in (Fig. 8). Nylon cord or rope is preferable to manila or cotton. The tie should be to a point close by to reduce the voltage gradient along the rope; also, leaving some slack length in the tie, if otherwise allowable, increases its insulation value. It would seem that a tie to one’s ankle would be preferable to one about the waist. Avoid a tie under the armpits.
7. If caught in a large flat area, try to get within the zone shielded by a projection as discussed above (Fig. 1). You should not be too close to the high point. If there are no dominant points, you should crouch as flat as possible; i.e., "sit small.”
8. Rappelling when lightning is imminent may be a calculated risk. It might be the quickest way to escape a danger zone. Minimum hazard is presented when the rope is of nylon and is dry, when one moves down with only feet touching the rock and when feet are close together. A shock could make one fall out of a rappel.
9. The writer disagrees completely with the common belief that you should discard ice axes, pitons and all other objects containing metal when lightning seems imminent. Their presence adds little or nothing to the electrical danger, and they may be badly needed in getting home over slippery and wet terrain. Metal as such does not "attract electricity.” The climber’s body, because of its greater height and lower electrical resistance, is much more likely to act as a lightning rod than is the ice axe.* You should not wave the axe high above your head. When carried normally, below the level of your head, it will contribute nothing to the hazard. The ice axe is best laid flat while sitting out a storm. A cluster of pitons carried in a pack or laid a little distance to one side will likewise do no harm.
10. No previous mention has been made of the effect of the kind of rock in a terrain on lightning hazards and their assessment. The writer does not believe that a correlation exists unless in a very secondary way. For example, variations in surface resistance caused by the rock have minor significance in comparison to the size of the stroke and one’s closeness to the point of impact.
First aid involves the usual treatment for electrical shock and burns; the normal problems of a mountain rescue will also be present. When breathing has stopped, artificial respiration by the mouth-to-mouth method is indicated. Electrical shock may be further complicated either by convulsions or by the irregular contractions of the heart muscle called fibrillation.(14) The latter may be suspected when one cannot detect a pulse. In the last few years a system of external chest massage to arrest fibrillation has become fairly common knowledge. It is taught in some first-aid courses, especially among power-company workmen. The patient is put on his back on a solid surface and a quick, heavy pressure momentarily applied to the lower breast bone, using the heel of one hand backed by the other hand. The ribs on either side of the breast bone should not be pressed as they may be fractured. The pressure is repeated at about one-second intervals for some minutes. Artificial respiration should also accompany this treatment. After the immediate first aid and safety measures, one may have to keep the patient out of traumatic shock and keep him as warm and comfortable as conditions allow. Also, later, treatment for burns may be necessary; electrical burns can be deep. The writer is not medically trained and submits this as only a general outline.
The hazards of lightning vary with circumstances. It is difficult to make statements that fit all cases. Conjecture has had to be applied in some cases in translating knowledge gained from the laboratory and other sources into another milieu. Thus the distance figures given above as guides can only be "educated guesses.”
When caught out in an electrical storm, take precautions quickly. Avoid direct strokes and their effects as best you can; insulate and place yourself to keep the momentary currents that flow over rock surfaces and along crevices from also going through your body; tie yourself in if you are where a severe shock might cause you to fall; and keep your ice axe! The simple act of seating yourself on a coil of rope—a few feet away from a rock wall instead of against it—could keep you from becoming a lightning statistic.
List of Citations
1. The Thunderstorm, U. S. Department of Commerce Publication, June 1949.
2. Thunderstorm Electricity, by Byers, Univ. of Chicago Press, 1953.
3. (a) "Lightning and the Mountain”, by James R. Wilson and Robin Hansen, (b) "Still a Bugaboo”, by Robin Hansen, Sierra Club Bulletin, V. 34, No. 6, June 1949, pp. 27-30 and 68-73.
4. "Accident on Bugaboo Spire, Purcell Range”, Appalachia, V. XXVII, No. 2, December 1948, p. 243.
5. The Lightning Book, by Peter E. Viemeister, Doubleday, 1961. L.C. No. 61-8908.
6. Protection of Non-Metallic Aircraft from Lightning. Part IV; Electrocution Hazards from Inductive Voltages, NACA Wartime Report W85. (Originally issued March 1945 as Advance Restricted Report No. 4128.)
7. ’’Lightning on Mount Adams, 1895”, Appalachia, V. XX, No. 4, June 1934, P. 149.
8. "On the Lightning Accident on Mt. Stuart in the Cascades”, by Ome Daiber, Appalachia, V. XXIX, No. 3, June 1953, p. 416.
9. "Colorado, Arapaho Glacier”, Accidents in North American Mountaineering; 1961, American Alpine Club, New York City, p. 27.
10. "On Rumford Whitecap”, by Charles B. Fobes, Appalachia, V. XXXII, No. 4, December 1959, p. 562.
11. "Wyoming, Wind Rivers—Koven”, by John Oberlin, Accidents in American Mountaineering; 1958, p. 13, American Alpine Club, New York City.
12. "Wyoming, Grand Teton National Park”, by William Siri, Accidents in American Mountaineering; 1959, p. 8, American Alpine Club, New York City.
13. "A Study of the Hazards of Impulse Currents”, by Charles F. Dalziel, Power Apparatus and Systems, No. 8, October 1953, American Institute of Electrical Engineers.
14. "Cardiac Arrest”, by James R. Jude, William B. Kouwenhoven, and G. Guy Knickerbocker, Journal, American Medical Association, V. 178, No. 11, pp. 1063-1070.
* The author is an electrical engineer in the High Voltage Section of the National Bureau of Standards, Washington, D. C. Illustrations are by Tom Culverwell, Southwest Harbor, Maine.
** See citations at end of article.
* The correlation between lightning rods and less definite conditions found in mountain climbing presents some complications. A lightning rod is a very good metallic conductor of a definite configuration. A mountain peak is a poorer conductor, variable in structure, and it may not be easy to analyze; no two are exactly alike. The statements made are necessarily generalizations but should fit most conditions.
* Measurements on two well-used ice axes showed resistance values of 500,000 ohms or more between the head and spike when wet and 1000 times this when dry. Thus the ice-axe handle has 100 to 5000 times the electrical resistance of the climber’s own body. Soaking the handle in linseed oil, or waxing it, will improve its resistance when wet.