Medical How does electricity kill

1. Sep 26, 2011

Pengwuino

So I was looking for a hilarious quote off this thread: https://www.physicsforums.com/showthread.php?t=326659 for a lecture I'm doing for electricity. Now, I've always been told that it's the current that kills you. However, this thread gives me the impression it's the frequency that can kill you, which actually seems to make more sense. So exactly what truely does it? Clearly a 5V 60hz AC source wouldn't do anything I'd imagine, so is it a combination of current and frequency? What would 100V DC source do? Confoosed! :)

2. Sep 26, 2011

mishrashubham

Electricity mainly kills by causing cardiac arrests or by burns. Proper functioning of muscles involves polarization and depolarization of the fibres and the electric current messes up with that.

Greater the voltage, deadlier the shock. Same goes for current. However if it gets to your heart, even small currents (in mA) can be fatal. However I don't know how exactly the current being AC or DC affects the lethality of a shock.

3. Sep 26, 2011

Staff: Mentor

Here, see if this helps.

I really like the explanation below. Any article that contains the words "wet meat" scores points in my book.

http://amasci.com/amateur/elsafe.html

This gets into frequencies as well.

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4. Sep 27, 2011

zoobyshoe

Both of those links have problems. The first asserts the human heart is on the left side, and the second is based on a half-understanding of what the word means: "Since these particles are always inside our bodies, we can't say that "electricity" is dangerous. Instead, it is the FLOW of charges which causes problems." He's creating a dichotomy that doesn't exist. The "FLOW of charge" is encompassed by the definition of "electricity":

http://en.wikipedia.org/wiki/Electricity

Anyway, as mishrashubum said, electricity could kill you by stopping your heart, or by burning you. In the latter case you become a resistor in a circuit, and to the extent you resist the flow of current you heat up. A direct hit by lightning could probably cause your bodily fluids to flash into steam and you'd blow up.

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5. Sep 27, 2011

Pythagorean

Shock is a complicated injury. 100V DC is enough to kill you if it's done right. AC isn't necessary, but it's more effective; the tales always go that Edison accidentally "invented" the electric chair as a demonstration to show how dangerous AC was.

P = IV, or power = current*voltage. I can't even imagine a way you'd get current (I) without a potential difference (V) to drive the current (get little ants to carry the charges away from each other? But that would generate a potential difference!), but even if you did, the power would be 0, so it would be difficult to do any damage with no power.

You can have I = 0 with a nonzero potential, though, but as long as I = 0, you'd theoretically be fine. On the otherhand, you could easily take the place of the component that's keeping I=0, or create a short circuit in the system, allowing current to flow.

At an extreme enough potential though, you'll just be depolarized and torn apart (water is already polar, but an extreme enough potential can make many more of your constituent particles polarized; I've never personally witnessed such a feat, but it doesn't sound comfortable). So stay away from particle accelerators and such.

6. Sep 27, 2011

Pengwuino

Hmm? I'm not sure why you thought I was wondering about something with no current.

7. Sep 27, 2011

Pythagorean

you weren't; I was demonstrating that voltage can kill you, so that old addage "it's the current that kills you" is a bit of a misrepresentation, and of course, DC can kill you, so it's not the frequency that kills you!

It's power that kills you, I guess. That's my final answer, Regis.

8. Sep 27, 2011

Staff: Mentor

That doesn't have anything to do with the accuracy of subject, besides
http://biology.clc.uc.edu/courses/bio105/respirat.htm

and is why the left hand is more dangerous

He's just trying to make it clear for "amateurs". It's still correct.

http://en.wikipedia.org/wiki/Electric_current

and

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9. Sep 27, 2011

zoobyshoe

It was actually quite deliberate, but, yeah, the whole point was to malign AC:

http://en.wikipedia.org/wiki/Electric_chair

10. Sep 28, 2011

Ivan Seeking

Staff Emeritus
DC is typically considered to be more dangerous than AC. Interstingly, and perhaps for the same reason,120/240 VAC can be more dangerous than 480 VAC. If you grab a 480 line, you tend to recoil away from the circuit [get blown back]. For lower voltages, esp 120 VAC, sometimes you can't let go, so the duration of the exposure can be much longer.

As for dramatic extremes, along the Feather River, in Northern California, there is a series of dams before the river hits the valley. One of the oldest of these used large, exposed copper pipes, as conductors coming out of the generators. When I toured that facility over thirty years ago, you could still see a large hole in the concrete along the corridor lined with the copper pipes. The tour guide explained that back in the fifites, I presume, when aluminum ladders first came out, some poor maintenance worker lost track of the position of his ladder and made contact with one of the copper pipes... As the story goes, pretty much nothing was left but the hole in the floor and a puddle of aluminum.

Last edited: Sep 28, 2011
11. Sep 28, 2011

rbj

but besides a high voltage source, you need low output impedance for it also to be really dangerous. consider the common electric fence, you want to stop the livestock, but you don't want to electrocute the farmer's 4-year old kid. those fence controllers have a high voltage winding with a lot of resistance in series in the windings. and a pulse interruption circuit.

this might be a little scary (lesson: don't climb power poles when high on PCP):

http://www.tb3.com/tesla/sparky.htm

12. Sep 28, 2011

bobze

It also depends on where the "shock" is applied. Getting hit on your finger, isn't the same thing as getting hit through the chest. Resistance of the body varies from person to person, day to day and place to place (on the body in question).

The old "50 mAMP safety" cutoff is BS, in my opinion. There is no way to predict how anyone individual (or their heart) will respond to different currents or voltages--So not getting zapped at all would probably be the best advice anyone could ever offer.

Further many people have undiagnosed, asymptomatic heart conditions--Such as junctional escape beats, that can easily be turned into VFib by the correct electrical stimuli.

13. Sep 28, 2011

Proton Soup

what if i jab the leads of your 5V source into the veins of each arm?

anyhoo, if you really want to get your nerd on (and you probably don't), then something like this might be up your alley.

http://www.unc.edu/~finley/BME422/Webster/c14.pdf [Broken]

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14. Sep 29, 2011

Pythagorean

15. Sep 30, 2011

Ivan Seeking

Staff Emeritus
So it was just for fun?

16. Sep 30, 2011

zoobyshoe

No, it was quite definitely developed for capitol punishment, under Edison's sponsorship. That should be clear from the Wiki article.

In a biography of Edison I once read it quoted him as later saying that people who's been executed in the chair had been "Westinghoused". He was deliberately trying to make Westinghouse's alternating current system seem highly dangerous. Edison, himself, was developing a DC power system. He just wanted to make the competition look bad.

17. Sep 30, 2011

Pythagorean

My understanding is exactly opposite, that Edison had the electric chair designed purely as a campaign against Westinghouse, and that he later (and somewhat reluctantly) divulged his research to the Governer of Albany who thought it was a more humane way of execution.

However, prior to that, there had been plenty "prototypish" devices that they electrocuted dogs and elephants with only to show the AC was dangerous, not to sell a capital punishment device.

You seem really certain, but I still am not convinced (especially not by a wiki article). Here's how I know the account (from a 1993 Newspaper, The San Francisco Examiner, cited by scope http://www.snopes.com/science/edison.asp" [Broken].)

An excerpt:

(emphasis mine)

I take the San Francisco Examiner's word over Wikipedia, but you may know a better source; I am by no means an expert at history.

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18. Sep 30, 2011

zoobyshoe

What I am saying is that he had this means of execution developed, intending for it to be used to execute people, not because he was interested in executions, but to make AC look bad. He wanted AC associated in people's minds with death and danger.

It could well be he balked at the idea of taking it from dogs to people at first, but he overcame those scruples and developed an electric chair intended to be used to execute people, the point being to make AC look bad. Hence, his hearty recommendation of "alternating machines" manufactured by his chief rival, Westinghouse.

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