How lightning kills and injures victims

A burst of lightning in the western sky behind the Lincoln Memorial, August 5, 2005. (Kevin Ambrose)

A burst of lightning in the western sky behind the Lincoln Memorial, August 5, 2005. (Kevin Ambrose)

If you’ve ever thought about being hit by lightning you probably assume that a lightning flash would come down from the sky, hit you, and that’s it. You’re dead.

First, lightning injures more people than it kills. In fact, approximately 90 percent of those lightning hits survive, but often with long-lasting neurological damage, says Dr. Mary Ann Cooper, a leading expert on lightning injuries.

Second, lighting that hits someone directly from the sky is called a direct strike, “which hardly ever happens,” says Ron Holle, a meteorologist with Vaisala Global Atmospherics, Inc., in Tucson, Arizona, which operates the National Lightning Detection Network.

You’ve probably heard that lighting which strikes a building can get into wiring or water pipes to kill someone talking on a phone with a cord or who is taking a shower. This happens, but such “contact strikes” are as rare as direct strikes. Direct and contact strikes each account for only 3-5 percent of lightning deaths and injuries.

lightning-chartGround currents, which spread out over the ground after lightning strikes, are the the big danger, accounting for 50-55 percent of all lightning deaths and injuries, says the National Oceanic and Atmospheric Administration.

When a lightning stroke, containing maybe 20,000 or more amperes of current, hits the ground all of this electricity doesn’t just disappear into the earth. It spreads out in the ground as a potentially deadly current with its voltage decreasing with distance from where it hit.

Such currents are lightning’s biggest danger because they affect large areas in circles extending out from where lightning reaches the ground, such as at the bottom of a tree.

High-speed, lightning research photos have shown ground-current arcs (sparks) as far as 60 feet from where lightning hit the ground.

If  you happen to be standing in a place affected by a ground current, it can travel up one leg, through your body―possibly stopping your heart or breathing―and down the other leg.  Ground currents are especially dangerous to animals, such as cattle, because the current passes through the entire body between the front and rear legs.  The greater the distance between where current enters and leaves a body, the more serious the damage.

The second most deadly kind of lightning strike after ground current is called “side splash” or “side flash,” which accounts for 30-35 percent of lightning deaths. This refers to lightning that jumps from an object to a person, or even from one person to another.

Side splash occurs because lightning follows the path with the least resistance to electrical current to the ground.

If you’re standing within a foot or two of a tree hit by lightning the lightning is likely to jump from the tree to you because to a lighting stroke you are a nothing but a bag of salty water with much less electrical resistance than a tree.

The red positive charges rising from the ground in this diagram are flowing along a channel known as a streamer. (National Weather Service)

The red positive charges rising from the ground in this diagram are flowing along a channel known as a streamer. (National Weather Service)

The third most common cause of lighting deaths and injuries are the upward leaders, also called “streamers,” that rise from high objects and the ground before lightning strikes.

To see how this works, let’s look at what happens in most lighting flashes that hit the ground.

A great difference between negative charge in a cloud and positive charge on the ground below causes a negatively charged stepped leader to begin zig-zagging toward the ground, breaking molecules of nitrogen, oxygen, and other gasses into positive ions and negative electrons. This creates a highly conductive path through the air, which otherwise has very high electrical resistance.

As a stepped leader nears the ground many streamers, with a positive charge, begin coming up, mostly, but not all, from high areas. When a leader and streamer connect a huge negative current begins flowing from the cloud to the ground. At the same time positive charge zips up the leader, creating the light we see as lightning.

If a streamer that connects with the stepped leader happens to be where you happen to be standing or crouching, a direct strike hits you. But, with many stepped leaders trying to connect, the odds are better that a streamer or streamers nearest to you don’t connect (with the stepped leader).

Nevertheless, you aren’t home free. Even the streamers that don’t connect can carry several hundred amperes of current, more than enough to kill or injure you even though you’re not actually hit by lightning.

All of this adds up to the safety rule that today’s lightning experts agree on: “When thunder roars, go indoors” to a building with plumbing and wires or into a metal vehicle with the windows rolled up.,

Forget what you might have seen or heard in now-outdated safety advice about squatting to avoid being the highest object around. While this might protect you from a direct strike, it won’t keep a more likely ground strike or a streamer from zapping you.

Related:

Don’t rely on folklore for lightning safety

Fishing leads U.S. lightning death activities

Ten shocking things that can happen if you are struck by lightning

Record low for lightning deaths in 2011 but tornado deaths third highest; why the disparity?

Stacking lightning bolts over Washington, D.C.

Dissecting a derecho bolt: more to lightning than meets the eye (and camera lens)

Lightning gone wild during Washington D.C.’s derecho

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