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In Jurassic Park when Tim, Dr. Grant and Lex are climbing the fence and Tim gets shocked, he immediately goes flying off the fence.

How realistic was this behavior?

enter image description here

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Unrealistic in every possible way

It follows the standard film trope of electric shock - a bright spark, smoke, and the character blown backwards by an "invisible hand". It also assumes mere contact with the electric cable is required, not considering the circuit as a whole. And finally it assumes CPR will work miracles afterwards. None of these are correct.

1) Electric sparks do not look at all like that, for starters. Anyone who's jump-started a car knows what sparks look like. The film version is pretty, but simply incorrect.

2) Smoke is rarely a feature of electric shocks. In order for smoke to occur, something needs to have burned. If that had happened to Timmy, he would have a continuous burn path through his body following the path of the current. This would be clearly visible at post-mortem. And he would very much be "mortem", because this would have been a large amount of current.

This relates to comments on the other answer - electric fences are intended to be painful but not fatal. The saying in the elec-eng world is "it's the volts that jolts, but the mills (milliamps) that kills". If it has to be more powerful to get through dinosaur skin, the voltage can be increased substantially, but the current must not be, otherwise you'll have dead dinosaurs. Electric fences do not appear threatening, so animals need to touch them at least once to discover that they are painful and learn to stay away from them.

3) An electric shock will certainly cause all your muscles to spasm, which can result in a substantial jump. I've experienced that myself. What you do not get is the effect shown in the film, where the electric shock acts like a piston hitting Timmy in the chest. Arms may straighten outwards, but legs straighten upwards.

4) As everyone knows from seeing birds perched on high-voltage wires, what is required for an electric shock is a path for the electricity. If there's no circuit, there's no current and hence no shock. (On transmission cables, the resistance of the wire can give enough voltage at high current for a shock at human arm spacing, which is why linemen need extra protection, but these are not high-current transmission cables.) Timmy would be in trouble when he touched the ground, but on the fence he's fine.

Unless the people who made the fence have been sneaky and rigged each wire at a different voltage, for example using a three-phase supply with the wires alternating phases. Touching adjacent or next-adjacent wires, as Timmy is doing, would then give you a shock too. This has a separate problem though, which is that the foliage in contact with the fence is shown sparking, meaning it is conducting electricity. As anyone familiar with Ohm's Law knows, this means a proportion of the current is going through the foliage instead of Timmy. Extrapolate for the amount of foliage on this short section of fence, and you can expect Timmy to experience no shock whatsoever.

5) If Timmy has been shocked and his heart has stopped though, CPR almost certainly won't do anything except keep his body ticking over for a bit. That's why we have defibrillators, because hearts are very reluctant to restart on their own. It certainly isn't the magic that films show it as. And moreover, if Timmy's had an adult pounding on his chest, he's going to hurt. CPR regularly breaks ribs and tears chest muscles, because essentially you're delivering a powerful sternum punch with high follow-through, over and over again.

  • 5
    As someone who's owned electric fencing, keeping foliage away from it is goal #1, and even for how incompetent Jurassic Park people are they probably would have noticed the fence keeps shorting out before now. Also for some humor re: no ground (not my video): youtube.com/watch?v=4SIT0aU_FRw – user3067860 Oct 28 at 13:01
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    Just as a by-the-by to number 5 - hearts always restart on their own, or they don't. No defibrillator can start it. Defibrillating is literally a shock to stop the heart, to stop the fibrillation, the wrong rythm. If the body is still capable to restart the proper rythm, it will start it all by itself. But if the patient is oxygen depraved and the nerves and electrolytes have lost their charge, this is very unlikely. CPR helps transport oxygen to the heart (and brain!) so that the body can restart the heart, and so the brain won't die (and leave the exercise futile) – Stian Yttervik Oct 28 at 13:55
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    Me testing a low power fence with dry rubber shoes by touching it: Man, this thing is barely working... Me testing it later with wet shoes and grass (rain): ZAP! Oh yea its working!! To the point of #4, yea, you have to be "grounded" to get shocked. – JPhi1618 Oct 28 at 19:09
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    Resistance at the contact point (through dry skin) could be considerably higher than resistance all the way through the body. Burns there without burning everyone along the current path is at least plausible. (But yes, that much current would likely be fatal). Also, the core of the body is wet and has lots of thermal mass to heat up before char temperature; current won't travel in a narrow "beam" through the body so there's much more volume per unit of heat. – Peter Cordes Oct 29 at 1:51
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    That's why we have defibrillators, because hearts are very reluctant to restart on their own. A defibrilator restarting a heart (The Magical Defibillator (TM)) is a movies trope as well. – WoJ Oct 29 at 19:44
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Focusing on Timmy flying away from a fence when he gets shocked...

Mostly realistic.

Electricity makes you clench and contract some of your muscles.

When a current above 10 mA travels through flexor muscles, such as the ones in our forearms that close the fingers, it causes a sustained contraction. The victim may be unable to let go of the source of the current, making the duration of the contact longer and increasing the severity of the shock.

However, it makes you spasm some other muscles

When a current above 10 mA travels through extensor muscles, it causes a violent spasm. If the muscles affected are the hip extensors that lengthen the limbs away from the body, the victim may be propelled, sometimes many metres away!

From this,

With the pulsing of an electric fence this cramping is transitory and the victim is able to retreat from the source of energy. [...] Electric fence energizers put out high voltage (around 8,000 volts), but very low amperage or current (around 120 milliamps). This is 120-thousands of an amp. It should not even kill a squirrel.

While Timmy would clench the fence momentarily, his legs would kick him away from it. He would probably not fall with his body vertical like he did, but other than that, it's a possible outcome.

Also, as Nathaniel suggested in the comments, Jurassic fences may be beefed up more than usual, which leads to the injuries received by Timmy.

Life-Pro-Tip: When checking if something is electrified, don't grab it with your palms! As Karan Shishoo said, There are cheap tools on the market to check if something is electrified. If you really do have to touch it, use the back of your hand, so you won't clench whatever shocks you!

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    Just adding a comment for safety, never check if something is electrified with you hands (or any part of your body for that matter). There are enough cheap tools on the market than can do the same without risk. – Karan Shishoo Oct 28 at 5:34
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    Most electric fences are very-high-voltage, very-low-current devices. Yes, you're going to go flying off the fence, but because it hurts like the blazes, not because of current-induced muscle contractions. – Mark Oct 28 at 6:29
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    @Mark I'm no expert in the field, but I'd expect animal fences to be designed for pain, not injury, so in a Jurassic-Park-like scenario where decisions are (mostly) rational, I'd expect the owners to have selected high-voltage low-current fences. – toolforger Oct 28 at 6:39
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    Just a minor commment: given that the fence is designed to repel dinosaurs, it's possible that its specs are stepped up a bit beyond what you'd expect from an ordinary electric fence. – Nathaniel Oct 28 at 11:36
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    I'd say that's the crux of it, not a minor comment :P Dinosaur != squirrel – Lightness Races with Monica Oct 28 at 12:10
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It depends. I work with electric fence on our farm all the time. If you are not grounded, you will not get shocked, so you can hang off an electric fence and not get any zap as long as you are not grounded out.

Our fences use a ground-return design, meaning every other line is a ground line. So you can get a nasty shock touching the hot and ground lines. But the design in the movie is a solid mesh design. So Tim would not get any shock at all unless he was touching the ground as well as the fence.

20,000V sounds like a lot, but it depends on the amperage. For cows, yaks, bison, and humans we run our fences at 6,500-11,000V. I can grab that with a hand, it isn't pleasant, and you jerk with muscle contractions, but not such a much. For elephants and rhinos they use 15,000-20,000V works fine. Not sure what would be required for a 7,000kg lizard killing machine.

The fence in Jurrasic park has a lot of plants touching it, that will eat voltage like mad, but the scenes where they are dealing with power systems seem to indicate they are pushing a lot of joules which can overcome the fence load. Our fences push 6-12 joules, and we can handle some pretty wet plant matter on the fences.

Anyhow, TLDR version: no, not remotely close to accurate.

  • 20,000 volts is at the upper end of what you can get from shuffling through carpet and the touching a doorknob. – Mark Oct 28 at 21:08
  • Is the fence a mesh design, or is the "mesh" part non-conductive? I see in the picture that there's a small number of very thick cables, with some much thinner wires in place as well. – user3757614 Oct 29 at 0:24
0

Movie/Dramatic Level of Realism

This infographic illustrates how every part of your body feels the terrible effects of electrocution especially with an electric fence built to stop a giant dinosaur like the T-Rex 🦖

Electric fence and electrocution effects on the body

He’d likely not be in the rest of the movie with that level of amperes as well as voltage. The amps are what kill you and wreak havoc on the body — the real question what the current level on the fence was.

  • Again, you need to edit the relevant information from the infographic into your answer, for the benefit of those with screen readers and to make it easier to read in general. It would also be useful if you could put some sort of figure on how much electricity it would take to cause these symptoms, and then we could try and compare it to the fence in the film. – F1Krazy Oct 29 at 15:35
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    I appreciate your enthusiasm - you've posted six answers in the past half-hour, half of which were on unanswered questions - but here on Stack Exchange we value quality over quantity and I suggest taking some time to make sure each of your answers is as high-quality as it can be before moving on to the next one. – F1Krazy Oct 29 at 15:38
  • I also recommend not self-deleting answers if you receive criticism on them, but instead either taking it on board and editing your answers to improve them, or simply ignoring it if you feel it's not applicable. IIRC, having too many deleted answers can trigger an automated answer ban. You're a long way from that yet, but since you deleted one of your previous questions after I commented on it, I just wanted to give you a quick heads-up. – F1Krazy Oct 29 at 15:40
  • Thanks everyone - I won’t be as enthusiastic then. I apologize for deleting the other answer for Revolver - I didn’t really care much for the movie (hence, why I deleted it 🤦🏻‍♂️) 👍🏼 Thanks for the heads up and I’d have to grab the MedSource journal to help with every effect. – Miles Price Oct 29 at 15:43
  • Also, the voltage, current and ohms would be important in gauging the proper level of electrocution. As for amperes (deadly at high amperes - likely not used for high value assets such as dinosaurs) and voltage (pure power and not always deadly) The difference would be astounding = Example: the effects of lightning on the body vs the effects of getting shocked due to working on a car without proper grounding when it comes to the differences between amperes and voltage – Miles Price Oct 29 at 15:49

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