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I have been reading about many cases in history of lighting striking and killing dozens even hundreds of animals, to be more specific quadruples, at the same time. Apparently this doesn't happen with small animals, only with animals that have a significant separation between their legs. Why does this happen.

Here is an article reporting one of the cases and it has an explanation that I didn't understand. https://www.google.com.co/amp/s/motherboard.vice.com/amp/en_us/article/78kewb/a-very-simple-explanation-for-how-lightning-killed-323-reindeer-at-once

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  • $\begingroup$ What part of the explanation did you not understand? Lighting (i.e., an enormous electric discharge) hits the ground, electric current radiates out along the wet surface of the ground in all directions from the point of the strike, some of that current flows up one leg of a wet animal, through its heart, and down another leg on its way to wherever it was going. A big lightning bolt can peak at more than 100,000 Amperes. It only takes a few milliamperes to send an unlucky mammal's heart into fibrillation. $\endgroup$ – Solomon Slow Oct 31 '17 at 20:33
  • $\begingroup$ @James because it said that a squirrel could survive, and said something about the distance of the legs, that part is very unclear to me. $\endgroup$ – whatDoYouMean Oct 31 '17 at 20:35
  • $\begingroup$ One factor is the heart rate of the animal. The smaller mammals have a much higher heart beat frequency than the larger mammals. It is easier to stop a slower heart. The momentum for a fast beating heart would tend to more better return to beating after an interruption $\endgroup$ – 0tyranny 0poverty Nov 1 '17 at 2:50
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because it said that a squirrel could survive, and said something about the distance of the legs, that part is very unclear to me

Every electric conductor has a property called "resistance." You may have heard that "electricity always follows the path of least resistance." That's almost true, but really, its only most of the current that follows the path of least resistance.

When there's more than one path for current to follow, the fraction of current that follows each path is inversely proportional to the resistance of the path. The path with less resistance gets more current and vice versa.

The resistance of an overhead power line is extremely low compared to the resistance of the body of a squirrel. -Especially if you compare it to the resistance of a squirrel's dry skin. When a squirrel walks along a line that is carrying current on a dry, sunny day; virtually all of the current will stay in the line, and only a tiny, tiny amount will go through the squirrel's body.

You can ignore the part about the squirrel touching the tree and the power line at the same time. That's a case where the squirrel's body would be the only path for current to flow. That is unlike what happened to the caribou.

What happened to the caribou was that lightning sent a huge amount of current (could have been as much as 100,000 Amperes at the point of the strike) travelling along the surface of the ground. The caribou were wet. And the resistance of the path through their wet skin and their bodies probably was not very different from the resistance of the ground that they were standing on. Therefore, a significant amount of current took the detour, up one leg, through the animal's heart, and down another leg instead of staying in the ground.

Like I said, a big lightning bolt can carry more than a hundred thousand Amperes. It only takes a few hundredths of an Ampere to put an unlucky mammal's heart into fibrillation.


P.S., Sqirrels in front of my house usually walk on the telephone wires and TV cable which are closer to the ground than the power lines. Those wires are low voltage, carry very little current, and they're insulated (i.e., covered in very high-resistance material).

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I wouldn't be surprised if it has something to do with "ground step potential". When a high voltage source, e.g a downed transmission line, touches the ground, the voltage does not go from the high potential to zero (ground) over an infinitely small distance, but over a measurable distance. This is in addition to the factors that james large mentions.

One reference I found states the voltage drops by half every 2.5-3 feet away from the energized source. So a human, or a deer, with their feet spread 3-4 feet radially from the source would see a significant potential difference between their feet, leading to a large current flowing through the body as james large details. A smaller animal would experience a much smaller potential difference and less current, and in the extreme case of a squirrel or bird on a power line, there should be no real potential difference between limbs, and thus no current. Also if the potential difference is low enough, it's not enough to cause significant current to flow due to the resistance of dry skin.

As a side note, don't go close to a downed power line for this reason.

Here's a DOE report on an incident that describes some of the details. Here's some info on human electrical resistances.

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