Author Topic: What kills people, current or voltage? Or something else?  (Read 26399 times)

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Offline rgawronTopic starter

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What kills people, current or voltage? Or something else?
« on: February 17, 2015, 11:27:37 pm »
Some people claim, that voltage is dangerous, not current, some claim otherwise. In my opinion, it's neither voltage nor current but the power. In order to do any damage to the body, some changes in its structure or behavior must be made, to make them, power is needed. Do you agree with that? Why?

While this may look like a trivial topic, opinions are varying, so I'm starting this thread.
 

Offline Phaedrus

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Re: What kills people, current or voltage? Or something else?
« Reply #1 on: February 17, 2015, 11:31:21 pm »
Current kills. Period. You have to have enough voltage to overcome your body's resistance, but once that condition is met it is the current that determines lethality.
"More quotes have been misattributed to Albert Einstein than to any other famous person."
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Offline rgawronTopic starter

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Re: What kills people, current or voltage? Or something else?
« Reply #2 on: February 17, 2015, 11:36:18 pm »
Even if the current is huge, but voltage is in uV or nV?
 

Offline CM800

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Re: What kills people, current or voltage? Or something else?
« Reply #3 on: February 17, 2015, 11:40:29 pm »
I do, when people keep asking these questions... again and again and again.

Current kills, but you need a voltage to push the current through you.

Licking a car battery would only kill you from lead poisoning or having to tear your tongue out to stretch it all the way across both terminals. While it is capable of supply huge amounts of current, It needs a resistance low enough to allow the voltage to push a lethal amount of current through you. A human body simply has too much resistance.
 

Offline AG6QR

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Re: What kills people, current or voltage? Or something else?
« Reply #4 on: February 17, 2015, 11:46:29 pm »
It's not either/or.  Voltage and current aren't independent of one another.  Ohms law says they're related, according to the resistance.  The resistance of skin and body tissue is highly variable, depending on how dry the skin is, how much pressure is applied, where the electricity is applied, etc. The resistance of the salt water inside our tissues is pretty low, compared to the resistance of the dry outer layer of skin.

If you insist on saying it's one or the other, it's more directly related to the current.  We can sustain a shock of thousands of volts when we touch a metal doorknob after walking across dry carpet.  But 50 volts can be fatal if the skin resistance is low.
 

Offline rgawronTopic starter

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Re: What kills people, current or voltage? Or something else?
« Reply #5 on: February 17, 2015, 11:50:05 pm »
So if sufficient voltage and current is needed, then we can agree that it's about power that kills/hurts?
 

Offline Phaedrus

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Re: What kills people, current or voltage? Or something else?
« Reply #6 on: February 17, 2015, 11:51:09 pm »
So if sufficient voltage and current is needed, then we can agree that it's about power that kills/hurts?

Nope.
« Last Edit: February 17, 2015, 11:53:47 pm by Phaedrus »
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Offline Whales

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Re: What kills people, current or voltage? Or something else?
« Reply #7 on: February 17, 2015, 11:53:04 pm »
Current kills. Period. You have to have enough voltage to overcome your body's resistance, but once that condition is met it is the current that determines lethality.

That's an approximation of the truth.  If the current is at a fatal level you could also argue the voltage is at a fatal level by re-arranging the equation.

It's better to break down how electricity can kill you by different means.  I only know of a couple:
  • Organ failure through communication interruption (eg fibrillating/stopping a heart, causing electrical issues in brain)
  • Dissipating lots of power in your cells -> organs cooked or blood poisoning from dead cells (burns)

Communication disruption
I don't know much about this, but it's why AC can be more dangerous than DC.  It's also why certain 'paths' (eg hand to foot vs hand to hand) can be less or more safe/dangerous.  Only tiny amounts of power/current are necessary for this.

Given that human R is decently high in most scenarios you need a reasonably high voltage for a effective amount of current to flow.  Hence the 'fear voltage' saying, which is slightly better than 'fear current' but still misses the complexity of some situations.  It is better advice however to give to an average joe, as most power supplies you can kill yourself on are constant-voltage of some variety.

Cooking
Ie raw watts over time.  In certain situations you are kept in the circuit because you lose control over eg your hands and they grip hard.  In other situations you release immediately.  Some current levels are actually safer than ones below them because they ensure you can't hang on to die  :o  but this is heavily situation dependant.


Overall I prefer not to tell people to fear current, as I've encountered people that think car batteries ("100s of amps")  are more dangerous than ("10A") wall powerpoints.  If anything say voltage is a better way to judge situations simply because it's statistically more likely people will electrocute themselves on a constant-voltage (AC or DC) source than a constant current or more complex one.

Opinions on 'safe voltage' levels vary
Depending on the country and guidelines you will find everything from above 40V is dangerous to above 100V is dangerous.  It really depends on the situation -- if you're sweaty and barefoot on a metal or damp floor, then think a bit more about that 50V AC supply a bit more than normal.  If you're in rubber boots and thinking about what you're doing with your limbs then over 100V constant-voltage supply is probably fine.

When I'm dealing with peers getting into electronics I generally say "please don't play with anything that can deliver over 40V without talking to me".  It's an overly safe threshold BUT I don't want them setting fire to their projects either  :)
« Last Edit: February 18, 2015, 12:23:24 am by Whales »
 

Offline rgawronTopic starter

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Re: What kills people, current or voltage? Or something else?
« Reply #8 on: February 17, 2015, 11:56:39 pm »
So if sufficient voltage and current is needed, then we can agree that it's about power that kills/hurts?

Nope.
why?
 

Offline suicidaleggroll

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Re: What kills people, current or voltage? Or something else?
« Reply #9 on: February 17, 2015, 11:59:17 pm »
So if sufficient voltage and current is needed, then we can agree that it's about power that kills/hurts?

No, it's the current through your nervous system that matters and can stop your heart.  The voltage that it takes to get there depends on your skin's resistance.  Stab the probes through your skin and the voltage required to get to a lethal current level is much lower.  The lethal current level stays constant, only the voltage (and therefore the power) changes with skin resistance, so it's the current that kills.
 

Offline Whales

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Re: What kills people, current or voltage? Or something else?
« Reply #10 on: February 17, 2015, 11:59:49 pm »
Electrical safety is not a one-sentence affair.   Nor is it a one-cause-of-danger affair.

Please always be aware that people in different situations will have different types of electrical hazards to deal with.

Also another point to consider: chemical breakdown of bodily parts to make them more conductive.  At certain voltages/currents/power levels the burning/chemical changes will decrease the effective resistance of a person.  This can be dependant on heat through power or minimum chemical energy required for a reaction through the form of voltage, but only the voltage across the affected area (generally a small proportion of total voltage).
« Last Edit: February 18, 2015, 12:05:23 am by Whales »
 

Offline Electric flower

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Re: What kills people, current or voltage? Or something else?
« Reply #11 on: February 18, 2015, 12:05:20 am »
Neither voltage or current alone kill you,
It's time while you are exposed to current, but to have current you need some voltage and resistance of something you want to kill.

All work and no play makes Jack a dull boy.
All play and no work makes Jack a mere toy.
 

Offline DanielS

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Re: What kills people, current or voltage? Or something else?
« Reply #12 on: February 18, 2015, 12:13:05 am »
So if sufficient voltage and current is needed, then we can agree that it's about power that kills/hurts?
You need enough voltage to pass enough current to disrupt normal heart operation but the voltage required to achieve that depends on how much resistance ends up in the path and the amount of current will also vary from one individual to another along with the specific path through the body.

The required voltage may vary 100:1 depending on circumstances but the share of current passing through the heart is always in the neighborhood of 30mA. So, current is a much more reliable measure of potential lethality: any source capable of delivering at least 10mA with enough voltage to deliver it on-contact is potentially lethal. A 5kV source that can only provide 10mA will cause local burns but is unlikely to be lethal.

It is a bit like working with CRTs: hitting a charged cathode (couple of pF charged at 20-50kV) is more likely to cause injuries from over-reacting to pain and surprise on accidental contact (ex.: dropping and shattering the thing) than the shock itself.
 

Offline electr_peter

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Re: What kills people, current or voltage? Or something else?
« Reply #13 on: February 18, 2015, 12:18:26 am »
Quote
What kills people, current or voltage?
Wrong question:
  • it neglects that current and voltage are not independent. They are dependant
  • Nobody/nothing is killing people. People die because of adverse electricity effects on human body
  • it neglects that there are more potential dangers from electricity than "current" and "voltage"
Such question shows complete misunderstanding of electricity. Questioner should consider additional education in this topic.
Answer is not simple. Effects on human body depends on electricity source parameters, human action and condition, environmental conditions, etc.
 

Offline Whales

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Re: What kills people, current or voltage? Or something else?
« Reply #14 on: February 18, 2015, 12:22:01 am »
Answer is not simple. Effects on human body depends on electricity source parameters, human action and condition, environmental conditions, etc.

 :-+

Online Mechatrommer

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Re: What kills people, current or voltage? Or something else?
« Reply #15 on: February 18, 2015, 12:25:07 am »
wrong... its the Will of the God, based on the Law that is written on the Tablet in the beginning of the Time, known or unknown to men. what is known is V = IR, as described by many people above... fwiw.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline rgawronTopic starter

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Re: What kills people, current or voltage? Or something else?
« Reply #16 on: February 18, 2015, 12:32:37 am »
Quote
No, it's the current through your nervous system that matters and can stop your heart.
IMHO heart's pulse is driven by electrical pulses from cells/tissues that produce those pulses, therefore they have their power. If power from external source is small enough, it will not disturb the signal (enough), therefore will not be lethal/dangerous.

I will present my point of view in a different form: let's say you have a tank of water, a wire is sunk in it and you want to boil the content. In order to do that, you need to supply enough power to the wire, so current * voltage has to be sufficient. Power is needed to perform the action.

I think, this is the same case here.
 

Offline c4757p

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Re: What kills people, current or voltage? Or something else?
« Reply #17 on: February 18, 2015, 12:40:17 am »
Some people claim, that voltage is dangerous, not current, some claim otherwise. In my opinion, it's neither voltage nor current but the power.

IMHO heart's pulse is driven by electrical pulses from cells/tissues that produce those pulses, therefore they have their power. If power from external source is small enough, it will not disturb the signal (enough), therefore will not be lethal/dangerous.

This isn't a matter of opinion. Electricity won't consult you before it kills you.
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Offline radioFlash

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Re: What kills people, current or voltage? Or something else?
« Reply #18 on: February 18, 2015, 12:50:08 am »
Check out Afrotechmod's video on the subject:

 

Offline KM4FER

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Re: What kills people, current or voltage? Or something else?
« Reply #19 on: February 18, 2015, 12:53:20 am »
Hey everybody, lets do a crowdsource experiment.

Grab your favorite multimeter.
Set it to measure resistance.
Grip one probe between your thumb and forefinger of the left hand, do the same with the other probe in your right hand.
Squeeze hard.
Record the reading.
Lick your fingers where you grip the probes and repeat the measurement.
Record the wet reading.
Report your results back here.

For me:  Dry ~700k,  Wet ~60k.

So what voltage would it take to put 30ma through my body.  Sorry, you can't calculate from these readings since the effect of the current flow will be to change the resistance of my body, just like a tungsten light bulb.

 

Offline gilbenl

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Re: What kills people, current or voltage? Or something else?
« Reply #20 on: February 18, 2015, 12:53:48 am »

That's an approximation of the truth.  If the current is at a fatal level you could also argue the voltage is at a fatal level by re-arranging the equation.

It's better to break down how electricity can kill you by different means.  I only know of a couple:
  • Organ failure through communication interruption (eg fibrillating/stopping a heart, doing in a brain)
  • Dissipating lots of power in your cells -> organs cooked or blood poisoning from dead cells (burns)

This response is closest to the truth, notwithstanding the response from ElectricFlower. The key component is time and thus power. For example, you could zap 2 "identical" people with 120VAC-One will live, the other one fibrillates and kicks it. The deciding factor is when in the cardiac cycle was the voltage applied. Also, referring to it as "cooking" is a bit misleading. Current lethality is a product of let go threshold. Regardless of how you navigate your way around ohms law, when your muscles experience about 10mA, they clamp and you are now inextricably tied to the source. You'll continue to hang on until your muscle proteins degrade due to the heat. In this sense, you are "cooking," but only because you've increased the time and the energy you're being exposed to. Odd are, however, you were dead long before you were cooked.

60 Hz AC is more dangerous because it more readily elicits reentrant circus movements in the heart, fibrillation and a really bad day.

Interestingly, your brain is generally safe-its 3lbs of fat and water. You will loose consciousness quickly because of excess electrical activity (notice I did not say voltage or current), but generally you'll recover. The most critical neurological consequence is loss of communication b/w your respiratory centers and your diaphragm during this time. Unlike your heart, you need regular input to your diaphragm to breathe. Look up something called "Ondine's Syndrome."

The overwhelming majority of deaths from electrocution are due to ventricular fibrillation and cardiac arrest. Some folks do get horrible burns and ultimately succumb, relatively rare as far as I know. Moral of the story: Amps and volts are virtually irrelevant-Its all about work over time. People can and do die from licking 9V batteries! (Edit due to folks missing the point)
« Last Edit: February 18, 2015, 01:25:00 am by gilbenl »
What doesn't kill you, probably hurts a lot.
 

Offline AG6QR

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Re: What kills people, current or voltage? Or something else?
« Reply #21 on: February 18, 2015, 01:01:59 am »
I will present my point of view in a different form: let's say you have a tank of water, a wire is sunk in it and you want to boil the content. In order to do that, you need to supply enough power to the wire, so current * voltage has to be sufficient. Power is needed to perform the action.

Actually, no.  To boil water, you've got to supply enough energy, not power.  You can supply a smaller amount of power over a longer time, or a larger amount of power over a shorter time.  It's true that the energy has to be supplied quickly enough to overcome the rate of heat loss to the environment, but that's about the only constraint on power.

But the mechanism of what's needed to boil water doesn't have much implication on what is required to stop the heart.
 

Offline helius

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Re: What kills people, current or voltage? Or something else?
« Reply #22 on: February 18, 2015, 01:06:19 am »
People can and do die from licking 9V batteries!
Bullshit. Please stop spreading urban legends.
 

Offline BravoV

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Re: What kills people, current or voltage? Or something else?
« Reply #23 on: February 18, 2015, 01:09:31 am »
Silly question  :palm:, you just can't over generalized only at one factor, make the conclusion just like that without the details.

Its all come down to measurable metrics/quantities in order to answer that completely.

Its like asking if a clean/non polluted water can kill people ?  >:D

Eg :
- Will inhaling water (eg:drowning) kills you ? A drop ? A CC ? A liter ? 5 liter ? 10 liter ?
- Will ingesting water (eg:drinking or injecting it into your vein  :-DD) kills you ? A drop ? A CC ? A liter ? 5 liter ? 10 liter ?

Its stupid right ? Like for example to conclude (or worst to debate) that only inhaling water will kill people.  :palm:



This isn't a matter of opinion. Electricity won't consult you before it kills you.

Spotted, another sig worthy quote.  >:D
« Last Edit: February 18, 2015, 01:18:49 am by BravoV »
 

Offline suicidaleggroll

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Re: What kills people, current or voltage? Or something else?
« Reply #24 on: February 18, 2015, 01:18:37 am »
You need enough voltage to pass enough current to disrupt normal heart operation but the voltage required to achieve that depends on how much resistance ends up in the path and the amount of current will also vary from one individual to another along with the specific path through the body.

The required voltage may vary 100:1 depending on circumstances but the share of current passing through the heart is always in the neighborhood of 30mA. So, current is a much more reliable measure of potential lethality: any source capable of delivering at least 10mA with enough voltage to deliver it on-contact is potentially lethal. A 5kV source that can only provide 10mA will cause local burns but is unlikely to be lethal.

It is a bit like working with CRTs: hitting a charged cathode (couple of pF charged at 20-50kV) is more likely to cause injuries from over-reacting to pain and surprise on accidental contact (ex.: dropping and shattering the thing) than the shock itself.

^ This

Think of it this way.  Due to ohm's law, you need all three, you can't separate them.  But what you can do is plot the lethal voltage/power/current required to kill somebody as a function of resistance.  Whether their hands are dry/wet, dirty/clean, in-tact/punctured, all matters.

When you plot it up, you see that the voltage required to kill somebody depends on resistance.  The power required to kill somebody also depends on resistance.  The current required to kill somebody does NOT depend on resistance, it's ~30mA regardless.  That's why we say that it's current that kills you.  Whatever voltage it took to get that 30mA across your heart, is what is required to kill you, and the power is whatever it happens to be as a result.
 


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