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Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Lightning Precautions

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Spring, summer (peak season), and autumn are the seasons during which we witness most thunderstorms, and during which people and animals are struck by lightning. The National Oceanic and Atmospheric Administration indicates that approximately 50 Americans are struck and killed each year by lightning.

One of the world's experts on lightning injuries is Dr. Mary Ann Cooper, who is Professor of Emergency Medicine and Director of the Lightning Injury Research Program at the University of Illinois at Chicago. This year, Dr. Cooper was the recipient of the Research Award from the Wilderness Medical Society at its annual scientific meeting held in Snowmass, Colorado. She is also senior author of the chapter on lightning injuries in the textbook Wilderness Medicine.

As Dr. Cooper has noted, most people seriously underestimate the risk of being struck and do not know when or where to take shelter. NOAA data indicate that of persons struck and killed by lightning, 25 percent were standing under a tree and 25 percent occurred on or near the water. It is logical that nearly all persons killed by lightning are struck outdoors, so it is very important that everyone who might be caught in a thunderstorm be able to make a rapid assessment of the risk, and seek the best shelter or protective positioning possible. This is a personal responsibility for most, and a very important skill for group leaders.

Here is some information intended to help you understand the behavior of lightning in order to improve avoidance techniques:

1. Lightning strikes the earth at least 100 times per second during an estimated 3,000 thunderstorms per day. Fortunately, the odds of being struck by lightning are not very great. The wise traveler respects thunderstorms and seeks shelter at all times during a lightning storm.

2. Thunder, which is always present with lightning, is attributed to the nearly explosive expansion of air heated and ionized by the stroke of lightning. To estimate the approximate distance in miles from your location to the lightning strike, time the difference in seconds between the flash of light and the onset of the thunder, and divide by five.

3. Lightning can injure a person in five ways:

A. Direct hit, which most often occurs in the open.
B. Splash, which occurs when lightning hits another object (tree, building). The current seeks the path of least resistance, and may jump to a human. Splashes may occur from person to person, or from a metal fence.
C. Contact, when a person is holding on to a conductive material that is hit or splashed by lightning.
D. Step (stride) voltage (or ground current), when lightning hits the ground or an object nearby. The current spreads like waves in a pond.
E. Blunt injury, which occurs from the victim’s own muscle contractions and/or from the explosive force of the shock wave produced by the lightning strike. These can combine to cause the victim to be thrown, sometimes a considerable distance.

4. When lightning strikes a person directly, splashes at him from a tree or building, or is conducted along the ground, it usually largely flows around the outside of the body (flashover phenomenon), which causes a unique constellation of signs and symptoms. The victim is frequently thrown, clothes may be burned or torn (“exploded” off by the instantaneous conversion of sweat to steam), metallic objects (such as belt buckles) may be heated, and shoes removed. The victim often undergoes severe muscle contractions—sufficient to dislocate limbs. In most cases, the person struck is confused and rendered temporarily blind and/or deaf. In some cases, there are linear (11/2 to 2 in, or 1.3 to 5 cm, wide, following areas of heavy sweat concentration), “feathered” (fernlike; keraunographism; Lichtenberg’s flowers—cutaneous imprints from electron showers that track over the skin), or “sunburst” patterns of punctate burns over the skin, loss of consciousness, ruptured eardrums, and inability to breathe. Occasionally, the victim ceases breathing and suffers a cardiac arrest. Seizures or direct brain damage may occur. Eye injuries occur in half of victims.

5. A victim struck by lightning may not remember the flash or thunder, or even recognize that he has been hit. The confusion, muscle aches, body tingling, and amnesia can last for days. With a more severe case, the skin may be mottled, the legs and/or arms may be paralyzed, and it may be difficult to locate a pulse in the radial (wrist) artery, because the muscles in the wall of the artery are in spasm. First-, second-, or third-degree skin burns may be present. Broken bones are not uncommon.
If a person is found confused, burned, or collapsed in the vicinity of a thunderstorm, consider the possibility that he was struck by lightning. The victim is not “electrified” or “charged”—you will not be jolted or stunned if you touch him.

6. If you are in the vicinity of a thunderstorm, seek shelter for the victim and yourself. Lightning can strike twice in the same place!

Lightning Avoidance

1. Know the weather patterns for your area. Don’t travel in times of high thunderstorm risk. Avoid being outdoors during a thunderstorm. Carry a radio to monitor weather reports. Lightning can lash out from 10 miles in front of a storm cloud, in seemingly clear weather. If you calculate (see above) that a nearby lightning strike is within 3 miles (5 km) of your location, anticipate that the next strike will be in your immediate area. The “30-30 rule” specifies that if you see lightning and count less than 30 seconds prior to hearing thunder, seek shelter immediately. Since thunder is rarely heard from more than 10 miles away, if you hear thunder, it is best to curtail activities and seek shelter from lightning. Do not resume activities outdoors for at least 30 minutes after the lightning is seen and the last thunder heard.

2. If a storm enters your area, immediately seek shelter. Enter a hard-roofed auto or large building, if possible. Tents and convertible autos offer essentially no protection from lightning. Tent poles are lightning rods. Metal sheds are dangerous because of the risk of side splashes. Indoors, stay away from windows, open doors, fireplaces, and large metal fixtures. Inside a building, avoid plumbing fixtures, telephones, and other appliances attached by metal to the outside of the building.

3. Do not carry a lightning rod, such as a fishing pole or golf club. Avoid tall objects, such as ski lifts and power lines. Avoid being near boat masts or flagpoles. Do not seek refuge near power lines or tall metal structures. If you are in a boat, try to get out of the water. If you are swimming in the water, get out. Do not stand near a metal boat. Insulate yourself from ground current by crouching on a sleeping pad, backpack, or coiled rope.

4. Move off ridges and summits. Thunderstorms tend to occur in the afternoon, so attempt to summit early and be heading back down by noon. In the woods, avoid the tallest trees (stay at a distance from the tree that’s at least equal to the tree’s height) or hilltops. Shelter yourself in a stand of smaller trees. Avoid clearings—you become the tallest tree. Don’t stay at or near the top of a peak or ridge. Avoid cave entrances. In the open, crouch down or roll into a ball.

5. Stay in your car. If it is a convertible, huddle on the ground at least 50 yards (46 m) from the vehicle.

6. If you are part of a group of people, spread the group out so that everyone isn’t struck by a single discharge.

7. If your hair stands on end, you hear high-pitched or crackling noises, or see a blue halo (St. Elmo’s fire) around objects, there is electrical activity near you that precedes a lightning strike. If you can’t get away from the area immediately, crouch down on the balls of your feet and keep your head down. Don’t touch the ground with your hands.

8. The StrikeAlert Personal Lightning Detector (Outdoor Technologies, Inc.) is the size and configuration of a pager and uses an audible warning and LED display to show the wearer how far away lightning is striking and if a storm is approaching or leaving.

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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.

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