Lightning: Scary enough to kill you without even hitting you!

COLORADO SPRINGS, Colo. — A lightning strike indirectly killed a man who had taken cover inside a tent with three other people, reported KMGH-TV in Denver.

This story illustrates one of the hidden dangers of high-voltage electricity in general and lightning in particular: splash current. A lightning bolt can kill you without even touching you.

When a lightning bolt strikes an object, the object becomes strongly electrified and may emit electrical discharges itself. These bolts, called "side splash," will arc from the object that's been hit to just about anything nearby, or to the ground, or both. By now, you probably know better than to stand beneath a tree during a lightning storm (and if you don't, you should–don't stand beneath a tree during a lightning storm!). The danger is only partly in being struck directly; even if by some stroke of fortune the riser coming from the tree makes contact with a descending stroke before the riser coming from your head does, if the tree gets struck you'll quite likely get hit by splash.

People can also be killed by lightning even if the stroke lands nowhere near. When lightning goes to ground, there will be an enormous surge of current in the ground that can extend away from the point of impact for some distance in all directions. This "splash current" can electrocute people standing nearby even if there's no arc and the lightning stroke doesn't hit them directly. This is what happened to the unfortunate person in the news article linked above.

The risk of injury or death from splash current increases as the amount of surface area in contact with the ground increases. This is particularly dangerous to campers, who may seek shelter from a storm inside their tent–and lie down in the tent. If more of your body is in contact with the ground, you are more likely to be injured or killed by splash current.

There are a couple of lessons in here. First off, high-voltage electricity tends to seek ground any way it can. A lightning bolt carries tremendous voltage at incredibly high current, and it tends not to be neat and tidy about the way it seeks ground. It'll arc all over the place, sometimes in unpredictable and counterintuitive ways. It can jump from object to object, it can jump between nearby buildings, and it can even jump all over the inside of a metal shed. (If you're caught in a lightning storm, most buildings provide excellent protection, but metal sheds and similar structures are an exception. A metal shed won't act as a Faraday cage because it's not completely enclosed; they don't have metal floors. So when lightning hits a shed, it has a tendency to produce arcs all over the inside–which is bad news if you happen to be there!)

The second is that there really isn't a safe place to be outdoors during a lightning storm. Prevention is the name of the game. In the story above, it took rescue workers three hours to reach the hiker and get him to the bottom of the mountain after he'd been hit by splash current–and by then it was too late.