Image copyright © C. Doswell, all rights reserved, used by permission
To stand against the deep dread-bolted thunder?
In the most terrible and nimble stroke
Of quick, cross lightning?
----King Lear, Act 4, Scene 7 -- William Shakespeare
Lightning is the second-most potent weather-created killer in the United States. It has been estimated that between 75 and 150 individuals are killed and up to 1,500 are injured each year from lightning strikes. From 1992 to 1995, the National Lightning Detection Network identified an average of 21,746,000 cloud-to-ground lightning flashes per year in the United States. Even though golfers living in Florida are the most likely victims, the fact that SAR teams regularly work on or near high peaks and ridges, the geographical features that help create the thermal clouds that generate lightning as well as providing lightning one of its most inviting targets, makes this phenomenon a serious safety concern.
Lightning creation begins with the formation of cumulonimbus (thunderhead) clouds. This process begins with warm,moist air near the earth and cooler air above. As this air is heated, usually by the sun, it begins to rise. This rising column of warm, moist air causes the air pressure and temperature to decrease. As this air begins to cool, it condenses and forms a cloud. As the air is pushed higher, it cools further and water droplets that can no longer be supported by the updrafts in the cloud begin to form. These droplets will eventually fall as rain, or if they are held high and long enough, hail will form.
During the formation of these thunderheads, it is thought by some scientists that the particles within the cloud suffer numerous collisions. The resultant larger particles acquire a negative charge, while the smaller particles become positive. Because of updrafts and gravity within the cloud, the larger and heavier negative particles tend to accumulate in the lower part of the cloud, while the smaller and lighter positive particles are carried towards the top. Another theory is that condensation and evaporation of water vapor, and the resultant negative or positive energy release is the cause of the energy build up that causes lightning.
The fact that opposite electrical charges attract each other while like charges repel allows the most common type of cloud-to-ground lightning. Once the negative electrical charge in the cloud becomes powerful enough, the air in between the cloud and the ground begins to ionize.
This allows the air, which is normally a poor conductor, to carry an electrical charge. This process begins at the bottom of the cloud and moves towards the ground (at 136,000 mph). The air initially ionizes in thin, tenuous paths. Each of these individual paths continuously branch out as they move towards the ground. Also, as the paths branch out, they move in separate steps, rather than as a smooth flow. All of these paths are therefore called the "stepped leader." Each time a new step is propagated (once each 50 millionth of a second), the entire stepped leader briefly lights up. But since the stepped leader moves so fast and the actual lightning stroke is so bright and occurs so soon after the stepped leader, it is not usually visible to the human eye.
Once this stepped leader gets close to the ground, the air also begins to ionize from the ground up. Since like charges repel each other, some of the negatively charged particles on the ground are pushed away by the approaching negatively charged stepped leader. This leaves an overall positive charge on the ground. This positively-charged electrical path, that then moves upward from the ground, is called a "leader." When a downward moving, negatively-charged branch of the stepped leader contacts a upward-moving, positively-charged leader, the connection is made. The intense heat created by this "first return stroke" (traveling at 62 million mph) lights up this path and creates visible lightning. (Even though it appears to the naked eye that the lightning is traveling from the cloud to the ground, it is in fact moving from ground to cloud.) In a narrow channel no wider than one inch, for approximately 1/1,000 of a second, a lightning strike can generate temperatures up to 50,000 degrees F, which is approximately 40,000 degrees hotter than the surface of the sun. During its 1 to 10 mile trip to the earth, the combined electrical output of a lightning bolt can be as much as one billion volts and 100,000 amps.
If more electrical charge flows into the bottom of the cloud immediately after the first return stroke, it will be forced into the original ionized connection path in a smooth rather than a stepped motion. When this "dart leader" reaches the ground, another return stroke is initiated. Since this process takes approximately 1/30th of a second, the individual dart leaders are invisible to the human eye. Therefore, if the dart leader process is repeated several times, it makes the lightning along the main connection path seem to flicker.
Anvil lightning is a particularly dangerous type of cloud-to-ground lightning, mainly because it is the most likely generation area for a "positive stroke." As the upper, anvil shape of a thunder cloud develops, a positive charge is created, and the cloud-to-ground process is repeated, except that the polarities are reversed. This is significant because these positive bolts can be ten times more powerful than the negative strikes, and can also last longer. More importantly, however, instead of traveling more or less straight down, this form of lightning arcs as far away as twenty-five miles from the main cloud. Therefore, anvil lightning can strike under blue skies. This is where the expression "a bolt from the blue" originated. As many as 20% of cloud-to-ground lightning strikes can be positive. They occur most often during the last part of a thunderstorm's life, during the winter months, and when pollution is high.
At the time of the first return stroke, the super-heated air within the channel expands rapidly, intensely, and explosively. Therefore, a shock wave is created. The initial shock wave moves faster than the speed of sound and can knock a person to the ground. It can also puncture a person's eardrums and render them deaf for a time.
The sound of thunder varies, depending on how far an individual is from the main connection channel. If the sound heard is a very loud, high-pitched clap, that is the sound of the shock wave. That obviously indicates an uncomfortable nearness to the strike point. If a person is close to the flash, but beyond the shock wave, thunder will sound high-pitched. Conversely, the further one is away from the flash, the more low-pitched will be the sound. Since lightning is jagged and crooked, the sound waves do not arrive at quite the same time, and the sound will seem to rise and fall.
The flash of lightning and its resultant thunder occur at virtually the same time, but because the speed of light is considerably faster than the speed of sound, lightning will be seen before it is heard. Therefore, the distance to the lightning bolt can be calculated, in miles, by counting the seconds between the flash of the lighting and the sound of the thunder and dividing the result by five.
Before Leaving Home
- Know that you CAN be struck by lightning. Never deny or minimize the possible danger. No one has a guardian angle that protects him/her from objective dangers.
- Be prepared for the possibility of lightning with appropriate knowledge, training, and equipment.
- Understand that activities undertaken in the mountains are generally goal-oriented. It is absolutely essential that these goals be kept in perspective. Extrinsic goals include making the summit, completing the route, getting to the next planned campsite, and, in the case of SAR, rescuing the victim. During the development of a thunderstorm, subjective emotional reactions ranging from mild stress to total panic can develop in an unprepared person. These reactions can be more hazardous than the thunder and lightning.
For example, as a climber, stress could begin to develop with a late start, and increase as he/she notices the beginnings of the formation of cumulus clouds. As the clouds get larger and darker, stress increases further. This can cause a climber to compromise her/his margin of safety regarding objective dangers. He/she might move a little faster than normal, place protection a little further apart, etc. Finally, total panic can develop if the climber sees lightning strikes on nearby peaks, hears deafening thunder, develops tingling feelings on his/her skin, hears a buzzing sound, has her/his hair stand on end, sees St. Elmos fire, etc. Therefore, added to the real risk of a lightning strike is panic which can, and probably will, result in reckless decision making and reflex actions that could likely cause a serious accident that would not be the direct result of an actual lightning strike.
Be prepared to turn around before this happens!
- Get a current weather report. A weather report can never be absolutely relied on, but it will provide a general idea of the conditions to expect.
In the Field
- Be aware of your surroundings. Be especially aware of any cloud buildup. If what you thought was puffy, fair-weather cumulus begins to exhibit vertical development and dark bases, it must be assumed that thunderstorms are likely. A tall cloud that begins to flatten out at the top is definitely a thunderhead.
- Never assume, even in the Sierra, that there will be a day without thunder and lightning. Begin the climbing or hiking portion of your trip in the early morning and plan to be in camp by early to middle afternoon.
- When you set up camp, make sure your tent isn't the highest object in the area or right next to it. If you do set up an unsafe camp and thunderstorm conditions develop, don't take the time to move camp. Just move yourself to a safer area until the danger has passed.
When Trouble Comes Your Way
Any time you see lightning and/or hear thunder, it is time to take action. It is generally recommended that you take shelter if the sound of the thunder arrives less than thirty seconds after the lightning flash. Since it takes five seconds for the sound of thunder to travel a mile, a thirty-second interval would indicate that the lightning strike was six miles away. Since a thunderstorm travels about twenty-five miles per hour (you can't outrun it), it could be overhead in about fifteen minutes.
If you can't see movement, it is a good idea to time the thunder and lightning again in about five minutes to determine whether or not the thunderhead is coming towards you. If it takes less time for the sound to reach you on this second check, you know you're about to have an unwelcome visitor. Last, but definitely not least, it is critically important to remember that positive cloud-to-ground lightning from the anvil area can strike as far as twenty-five miles ahead of a thunderhead and can appear to originate in a clear, blue sky.
In the last analysis, it should be understood that there is no distance from a visible thunderstorm that you can see that is completely safe.
It is also recommended that you not resume your activities until at least thirty minutes have passed since you last heard thunder.
Before It Gets Here
Remember that there is no place that is absolutely safe from a lightning strike. However, some places are safer than others.
If you are obeying the thirty-second rule described above, you will have approximately fifteen minutes until the storm arrives. Use this time to find the best available spot. However, action must be taken immediately if your hair begins to stand on end, your skin begins to tingle, or a buzzing is heard. If you hold your arm close to a color TV screen, you will know what it feels and sounds like. Blue halos, which are called St. Elmo's Fire, can also begin to form around objects. In any case, once you decide on the best spot, stay there. You made this decision when you had some time to plan and think.
Avoid being the tallest object(s) in your immediate area. Lightning tends to directly strike the tallest object in a given area because, whatever that object is, it is a better conductor than the surrounding air.
Avoid being near the tallest objects in your immediate area. Current from the strike can jump from the object struck to you (side flash or splash strike). Also, when lightning hits the ground, especially wet ground, the current spreads out like ripples on water (ground current or step voltage). Since the human body is also a better conductor than the earth, if you're close enough to the object struck, a considerable amount of current will travel up the leg closest to the stroke, and back down the other. Lastly, the shock wave, because of its violence, can cause various types of injuries (blunt trauma).
Avoid shallow caves, alcoves, big isolated rocks, and overhangs. Electricity tends to take the shortest path, and this shortest path might be from one edge to the other through you. A crevice or crack, especially when wet, also provides an excellent electrical path.
Avoid water. It is an excellent ground current conductor.
If below timber line, try to find a large area where the trees are generally the same height and put yourself in the middle of it. This makes all the trees more or less equally vulnerable to a strike, and thus lowers the odds. It is also a good idea to observe the trees in the area to see which ones have been struck before. This could give you a good idea of areas to avoid. In any case, do not place yourself any closer to a tree than is absolutely necessary. Stay out of clearings or meadows. Pick the driest possible area.
If above timber line, descend as quickly as possible as low as you can in the time you have. You never want to be so high on a peak that you're actually in the cloud. If you're in the cloud, in addition to cloud-to-ground lightning, there are the addition problems of cloud-to-cloud and intra-cloud lightning which are both much more common occurrences. If the thunderstorm catches you on a ridge, place yourself at its lowest point, which will usually be towards the middle.
If you find yourself just below the summit or near a pinnacle or other high point, place yourself on a flat ledge or gentle talus slope (avoid steep slopes) that will allow you to be a minimum of four to six feet away from the nearest vertical wall, but no further than the height of the pinnacle or high point. Sit parallel to the wall. If you are anywhere near an edge, tie yourself in. Even a small amount of electricity can cause you to lose control of your muscles and balance for an instant. The noise and flash of a strike can distract you and also cause a loss of balance. Avoid large, flat areas. Again, pick the driest possible area.
Assume the position: Crouch down as low as possible, on the balls of your feet with your feet close together. Place an insulating layer, such as a sleeping pad, coil of rope, backpack, etc. under your feet for ground insulation. Lower your head so that it is below your shoulders.
Cover your ears with your hands to help protect your eardrums from the shock wave of the thunder. If you're in a group, put as much distance as possible between each person. Remove any metal objects. Metal does not make it any more likely that you will be struck, but if you are struck, any metal on your body can cause serious burns through induced current.
If There are Victims
- The most important rule of response, as in all emergency situations, is to create no more victims. If the victim is in a high-risk area and/or there is still a thunderstorm in the area, wait! Lightning can, and usually does, strike the same places more than once. If rescuers violate this most basic rule and approach the victim while lightning danger is still high, to protect the rescuers from themselves, it is best to immediately move the victim to a safer area before initiating first aid procedures. While in the strike area, rescuers should remain as low as possible.
- Once a victim can be safely approached, he/she must be protected, as much as possible, from further injury. The victim is safe to touch; she/he does not carry an electrical charge. A decision must immediately be made as to whether or not to move the victim to an area less likely to be struck by lightning. This decision would be based on the victim's injuries and the likelihood of another lightning strike in the immediate area. Again, while in the strike area, rescuers should remain as low as possible. If there is more than one injured person, treat the ones with cardiopulmonary problems first, since this is the highest risk factor.
- Perform primary survey. The brain is the organ most negatively affected by lightning. While it's true that a lightning strike can cause a cardiac arrest, it is initially, in most cases, in the form of asystole instead of fibrillation. Therefore, the heart will normally begin beating again relatively soon. The brain, however, takes longer to recover. Since the brain controls respiration, rescue breathing may be necessary for at least an hour or more. If rescue breathing is not continued long enough, hypoxia can force the heart into ventricular fibrillation which will result in death. Victim may also lose consciousness, but unless there is a head injury, it will normally return spontaneously. Hearing loss can occur because of the close proximity of the shock wave from the thunder. Mental confusion and memory loss, paralysis of extremities, and seizures may also be present.
- Perform secondary survey and treat the symptoms. Lightning is direct current which is much less dangerous than household alternating current. Also, even though there is extremely high voltage and amperage associated with lightning,contact is of very short duration. Therefore, while some of the electrical energy from lightning does penetrate the body, most of it flashes around the outside of the body, especially if the body is wet. (If the body is wet enough, the moisture can be vaporized so quickly by the extreme heat that it will literally blow the clothing off the victim.) This means that there is not likely to be serious, deep burns. Thermal burns might be present if the victim had metal on his/her person, or if her/his clothing caught fire. Serious electrothermal burns are possible if the lightning passes completely through the body. The vascular and nervous systems are the usual pathways. If this is the case, there will be deep burns at both the entry and exit points and wherever there was direct body-to-metal contact.
- Treat for hypothermia, especially if the victim is wet.
- Do not administer fluids unless absolutely necessary.
- Get the victim to a doctor. Because the treatments are very different, make sure that the doctor understands that the victim has suffered a lightning strike and not an accident with man/made, AC electricity.
For additional information about Lightning visit these sites:
- Storm Safety! - for Kids - includes links with information about different types of severe storms, as well as preparedness checklists that families can use at home. (Thanks to Claire Watkins, Girl Scout Leader, for this link)
- NOLS Backcountry Lightning Safety Guidelines in Acrobat PDF format.
- National Lightning Safety Institute
- National Lightning Safety Institute Personal Lightning Safety Page
- National Severe Storm Laboratory (NSSL) section of the National Oceanic and Atmospheric Administration
- The NASA Global Hydrology and Climate Center Lightning Team site
- National Geographic Society Lightning site
- View a current map of lightning activity in the United States at Lightning Explorer
- The Science Behind Lightning - extensive resources and training materials