Lightning Hazards & Safety

Lightning Hazards & Safety

by Rick Curtis

I always teach our student leaders how to deal with lightning. It's never a very popular protocol, being crouched in the lightning position in the middle of the night in a thunderstorm, but the recent tragedy involving a Boy Scout troop backpacking in the Sierras which left a Scout Master and a child dead points out how serious the danger can be. Summer storms are common, particularly in the mountains so everyone should be prepared to react quickly and decisively when a thunderstorm approaches. The following information is adapted from my chapter on Weather in the Second Edition of The Backpacker's Field Manual.

Rick Curtis

Where does lightning come from?

In a mature thunderhead strong negative charges form in the base of the cloud, while a layer of positive charges forms at the top. Since like charges repel each other, the negatively charged base of the cloud has an effect on the electrical charges on the ground beneath it, 'pushing' the negative electrons on the ground away and leaving an area of positive charge directly beneath the cloud that follows the cloud as it moves.

Normally air is normally a poor conductor, however when the electrical differences between the cloud and the ground become great enough, even air molecules will conduct an electrical current. That's what a lightning flash is, a flow of these separated positive and negative charges back together again along ionized air. About 85% of lightning occurs within a cloud. You see this as cloud flashes, often referred to as sheet lightning. This is nature's way of trying to 'equalize' the electrical differential between positive and negative charge.

Cloud-to-ground lightning, (10-15% of lightning strikes), begins at the base of the cloud. An invisible stroke of negatively charged electrons known as a stepped leader zigzags tens of thousands of feet down towards the ground. When the negatively charged stepped leader gets to within a few hundred feet (50 to 100 meters) of the ground, a positively charged upward leader or streamer leaps off the ground toward the stepped leader, typically from a tall object like a building or tree. There actually may be a number of streamers trying to make contact with the leader, only one will connect. Once the connection is made the electrical circuit is complete; a rush of positive charges from the ground flows up into the cloud and negative charges flow from the cloud into the ground. The lightning flash that you see is the flow of charges from the ground to the cloud. The suddenly electrical charge releases an incredibly amount of heat (more than 43,000°F (24,000°C)). The air immediate around the lightning expands violently, and then contracts creating a sound wave--thunder.

Storm Distance and the 30/30 Rule

Thunder, the sound of the super-heated air around the lightning strike travels about one-fifth of a mile per second (1/3 of a kilometer per second). To determine the distance between where the lightning strike hit and your position count the number of seconds between the lightning flash and the thunder, and divide by 5. (For kilometers divide by 3.)

If the thunder happens within 30 seconds of the lightning, then the storm is within 6 miles (10 kilometers) of your location. Lightning safety experts consider this the strike danger zone and advise people to follow the 30/30 rule. Take immediate precautions when thunder is heard within 30 seconds of the lightning flash and wait for 30 minutes after the last thunder is heard to resume your activity. In most backcountry settings you simply can't 'stop' being in the outdoors, but you should find a safe location and stay there until the storm has passed. While the lightning is still miles away some storms move at 35 to 40 miles per hour (56 to 64 kilometers per hour), so the lightning can be right on top of you within minutes. If you see a lightning flash and don't hear any thunder then the storm is 15 miles (24 kilometers) or more away (the sound waves won't travel past that distance). So you don't need to start taking precautions, yet, but continue to monitor the storm.

Warning Signs of Lightning

Any or all of the following may indicate the possibility of imminent lightning:

• Thunder, even without any visible lightning.
• A sudden cloudburst of enormous raindrops or huge hailstones.
• A fast-moving cold front; these often trigger thunderstorms along a squall line ahead of the front as it pushes warm moist air upward. A change in wind direction with a sudden blast of cold air is often an indication of an incoming cold front.
• Signs of highly charged air--any of the following signs is an indication of serious lightning potential: hair standing on end or crackling; crackling noises or buzzing in the air; small sparks given off around metal objects; bluish glow around objects, known as Saint Elmo's fire.

Lightning Dangers

A Direct Strike

Direct lightning strikes are rare, but like the Boy Scout situation described above, they do occur. Almost anything can send up an upward leader. Typically the upward leader that 'wins' will come from the point with the least resistance to conducting electricity and/or the closest point to the stepped leader. High and relatively sharp points like radio antennas, mountain summits, sharp ridge lines, trees, or a standing person are most susceptible.

Side Flashes

Side flashes are extremely dangerous and account for a significant percentage of lightning injuries. As the return stroke travels to the ground, the object that sent up the upward leader may not be the best conductor of electricity. If the return stroke encounters electrical resistance it may 'arc off' that object to something else looking for an easier path to ground. Depending on how well grounded the object is, a side flash can arc 30 to 50 feet (10 to 15 meters). The arc distance for a 'moderately' well-ground tree is 16 feet (5 meters). Unlike ground current, which dissipates as it spreads out, a side flash carries a full electrical current. Side flashes can arc through the air or along the ground. Standing too close to a tree that is struck by lightning can result in being hit by a side flash with the same dangerous result as a direct strike.

Ground Currents

Once the lightning hits the ground, the electrical current spreads out in all directions along the ground following numerous paths of least resistance, dissipating as it goes. This is known as ground current, and injuries from ground currents are much more frequent than direct strikes. Ground current pathways include cracks and crevices filled with water, wet rock, wet climbing ropes, root systems, and cables along the ground. In some cases the easiest path may be to 'jump' across a gap of ionized air. This is known as a spark gap. This can occur at the openings of caves or under overhangs, where it is easier for the current to jump across the gap than to travel all the way around. If you are between the two sides of the gap, the current will flow right through you, so taking shelter at the opening of a cave may be more hazardous than being out in the open. When lightning strikes the water it dissipates in all directions; being in or on the water can put you in the path of ground current. Ground currents can be as dangerous as direct hits if you happen to be in their path and can result in thermal burns or cardiac arrest.

Protection from Lightning Strikes

To minimize your risk from lightning, your goal is to find the location that is least likely to send up an upward leader. Obviously, the major sources for upward leaders are things like mountain peaks, exposed ridges, and tall trees. You want to get away from these objects, but if you get too far away--out into an open field, for example--you may set yourself up as another likely source. For example, if you are near a pinnacle, stay inside a zone where your horizontal distance from the pinnacle is about one to one-half less than the pinnacle's height above you. It is best if the pinnacle is five to ten times your height to get a reasonable distance away from the potential strike location. This assumption is based on how a lightning rod works.

• Get off of summits, ridges, pinnacles, or any other place that is the highest location around. Even a few yards (meters) lower may offer some protection.
• Stay away from taller trees. If you are in a forest, try to find a group of lower trees that are less likely to be a strike site.
• If you are in the middle of an open field, the best thing to do is get into a low-lying area and assume the lightning position.
• If you are on the water, get to shore.
• Stay out of depressions, gullies, or drainages that may have water flowing in them.
• Find a position partway down a slope. Dry or well-drained ground is best.
• Avoid caves and overhangs unless they are clearly dry and spacious. These are usually part of a larger system of cracks and fissures, which are likely conduits for ground currents, especially if they are wet. Don't seek shelter in caves, under boulders or overhangs, or in bunkers unless they are dry and unless you have at least 20 feet (6 meters) of headroom and 4 feet (2 meters) of space on every side.

Where You Want to Be

• In the lighting position.
• Crouching on top of your pack.
• Crouching on top of a boulder that is resting on top of other rocks.

What to Do in a Severe Lightning Storm

Most lightning storms move away fairly quickly. With good rain gear, you should be able to stay relatively dry until the storm has passed, even out in the open. Hypothermia could be a problem if you become wet, but that's a secondary problem compared to imminent lightning danger. Here is what you should do if you are in immediate danger from lightning:

1. Spread Out If the group is in an area of high lightning danger, the group should not wait out the storm huddled together. Split up but still be within sight of each other--20 feet (6 meters) apart or more--unless this puts some people in a site with a higher strike potential. The survival of one person whose heart or breathing has stopped as a result of a strike may depend on prompt action by companions. If you don?t already know it, learn CPR.
2. Assume the Lightning Position Anytime thunder is 30 seconds or less from the lightning, the storm is within 6 miles (10 kilometers), and you should assume the lightning position. There are two basic positions, one is a crouch position with your feet close together and your butt off the ground. The other is sitting down with your arms crossed at your chest. In either position your hands should not be touching any part of your body below your waist (such as your knees). Don't lie down on the ground. Don't put your hands on the ground. If possible, you can crouch on top of a dry, insulating material like a foam pad or your pack.
   
   The idea behind the ligtning position is to channel any electric current through less critical areas of the body (the legs). In the lightning position if you were in the path of a ground current, it would travel up one leg and out the other, minimizing the parts of the body affected. If a hand is on the ground (or on any other part of your body below your waist), the current could just as easily flow up through the arm and out a leg traveling directly through the major organs, including your heart, potentially causing significant organ damage including cardiac arrest.

Crouch Position

Seated Position

Lightning Injuries

Electrical currents can cause the heart to stop, respiration to cease, thermal burns, muscle spasms, brain and nerve damage, and initial blindness. The extent of injury depends on the amount of current, the duration of the current, and the current's path through the body. With a direct strike or side flash, the current is usually so large that the results are fatal. Ground currents can be significantly less powerful, and the current path makes a major difference. If person is lying down, the current can enter through an arm and exit through a leg traversing all the major organs and causing significant damage and frequently stop the heart. If the person is crouching in the lightning position with hands off the ground the current could go up one leg and down the other without passing directly through the heart. Other injuries from lightning include ruptured eardrums, burns and even traumatic injuries since a direct strike can literally hurl a person many feet/meters through the air.

Treatment

The most dangerous situation in a lightning strike is that the heart may stop beating. Be prepared to administer CPR. Lightning is one of the few CPR situations where you may be able to revive someone without advanced life support so continue to do CPR as long as possible. Also, there may be electrical burns that can cause volume shock. Anyone who has been struck by lighting or ground current must be evacuated for advanced medical care.

Lightning Resources

• National Weather Service: ­ www.nws.noaa.gov
• The Weather Channel: www.weather.com
• Colorado Lightning Resource Center - www.crh.noaa.gov/pub/ltg.shtml
• Lightning Resources USATODAY.com - www.usatoday.com/weather/resources/basics/wlightning.htm
• National Lightning Safety Institute - www.lightningsafety.com