Question about being killed with electricity...

Discussion in 'General Electronics Chat' started by steev, Jun 16, 2011.

  1. steev

    Thread Starter New Member

    Jun 12, 2011
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    Hi Everyone,
    I've got a very basic knowledge of electricity so please excuse this question!!!
    Someone once told me that "amps kill, volts don't"
    Is that true?
    I suppose they meant that - in theory - you could have a mains 110v or 220v / 1amp running through your body and it wouldn't kill, but 110v/220v at, say, 50 amps would kill...?
    Or 4000v at 1amp wouldn't but 4000v at, say, 25 amps would kill.
    not that I want to find out.......
    These are only examples and I realise they're not practical mains power supply types!!!!

    Steve
     
  2. Wendy

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    Mar 24, 2008
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    True, but misleading. Volts breakdown skin resistance, and the amps finish you off. You can be knocked on your butt with 12VDC. If the current was introduced through the skin (say with needles) it would likely be fatal if directed through the heart. Current path is also important.

    So if you run into a low voltage system with lots of amps you are likely safe, if it is a high voltage system with low current it can be lethal (it only takes 10ma or so to kill).

    This subject comes up every so often.
     
  3. cjdelphi

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    Mar 26, 2009
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    I once had a 380v disposable flash capacitor discharge (freshly charged too) on me on 1 hand and discharged through my other, yes 2 sparks almost at the same time, weird sensation followed by a numbness in the arm that got zapped, it felt like a very quick burn, it left to red dots/puncture holes... :)

    Anyway This got me thinking, I got out the multimeter, when I grip hard, I get the resistance down to about 160k ohms, loose grip, 250kohms... my hands are very dry, it's also winter and im a bit cold too.. so I just wrote a quick 8 line program to output, and the figures don't make much sense, do i have my maths wrong?...

    Something's not adding up? and that's with a tight grip.....
     
    Last edited: Jun 16, 2011
  4. t06afre

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  5. t06afre

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    NO NOT very likely. I guess the current from a multimeter or a 9 volt battery could kill if you drove the measurement probes directly into the heart. But what situation would cause that to happened:eek:. If things escalate to such a level. You will most probably die any way
     
  6. cjdelphi

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    Mar 26, 2009
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    No wonder... it's 10uA not 10ma, now my maths makes sense...

    [/quote]
    If an electrical circuit is established by electrodes introduced in the body, bypassing the skin, then the potential for lethality is much higher if a circuit through the heart is established. This is known as a microshock. Currents of only 10 µA can be sufficient to cause fibrillation in this case.[citation needed] This is a concern in modern hospital settings when the patient is connected to multiple devices.
     
  7. cjdelphi

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    Mar 26, 2009
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    I think you'll find it's already happened to someone in the navy i think he was, he dug the probes in to see his internal resistance and well, died....
     
  8. bertus

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    Apr 5, 2008
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  9. t06afre

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    To me this sounds like pure gobbledygook. Do you have any credible references to this story.
    By the way. In order to get proper measuremnts on the skin electrical properties you need to use biopotential electrodes. The current flow in the human body is due to ion flow, not electrons. A biopotential electrode is a transducer that senses ion distribution on the surface of tissue, and converts the ion current to electron current. The skin conductance is only linear if the current density is less than 10uA pr cm^2 of skin
     
  10. TBayBoy

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    May 25, 2011
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    Just to throw in somethings here, the body is measured in impedance not just resistance, also energy flow past the skin surface requires special licensing (in North America at least) so don't just willie nillie start to experiment. :)

    Finally, newer defibrillators on the market, measure body impedance first with a "probe signal" then adjust the level of shock to deliver all without puncturing the skin, so barrier is more a biological term rather than electrical one. :)
     
  11. someonesdad

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    Jul 7, 2009
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    Folks who fool around with electricity should have some order-of-magnitude estimates of what currents are dangerous. It's not terribly important whether the current is DC or AC, although the body's sensitivity to higher frequency currents falls off a bit with increasing frequency (but don't interpret that to mean that the higher frequency currents are harmless, as anyone who has gotten an RF burn will attest to).

    I emphasize -- these are order-of-magnitude numbers. Do proper research if you want "exact" numbers, although the clinical variations between humans and shock situations will add fuzziness, not to mention that it's difficult to get exact figures in the laboratory without injuring or killing the subject, something most folks would probably object to, particularly the subject.

    Humans start to sense electrical currents around 1 mA. This is why leakage current specifications usually set an upper limit of about 500 μA or less. A current on the order of 1 mA can be hazardous -- but not directly. The reason is that a shock can startle a person and cause a reflex action -- which might cause some harm. Think of being next to a sharp sheet metal edge and jerking back when you get a shock, giving yourself a nasty cut.

    Around 10 mA is where it can become difficult to let go of a conductor when you're getting a shock. Half of this value is where most ground fault interrupter circuits are designed to open (the ones I've measured all trip between about 4.5 and 5 mA).

    100 mA is where ventricular fibrillation occurs (I've seen the range quoted from 100 to 200 mA). This is an abnormal pumping action of the heart (it quivers and doesn't pump) and leads to death in short order because little blood is being pumped.

    Currents 1 A and above are where burns happen. They can be especially nasty when associated with an arc flash -- a plasma caused by high currents that can be in the tens to hundreds of thousands of amps (or more). This is why, for example, you want to use Cat IV rated DMMs when working on primary electrical feeds.

    I've seen the statements about the sailor testing himself with an ohmmeter and dying from a shock, but I've never seen a properly-attributed reference to it. Thus, I consider it an urban legend/hearsay until otherwise debunked. Modern digital multimeters measure resistance by supplying a constant current through the unknown resistance. For example, my 20 year old Fluke 83's manual specifies the maximum typical short-circuit current when measuring resistance to be 0.7 mA (my meter's actual value is 286 μA). It would be hard to see that current level causing a problem with the probes touching skin, but I suppose if you jammed the probes to where they were within a mm or two of the heart or in the brain, you might have some shock issues. Again, the subject will probably object though.

    You can measure the short circuit current of your multimeter's resistance ranges by connecting the leads to another multimeter that's set to read current. The lowest resistance range will have the highest current.
     
  12. nsaspook

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    Don't forget that the shock might not be the thing that kills you. I got hit once by under 50 volts while on a step stool. When the world refocused around me I has flat on my back about 6 feet from the stool with a large bump on the side of my head from the fall. The damage on my finger was just a little redness but the fall could have broken my neck.
     
    Last edited: Jun 16, 2011
  13. steev

    Thread Starter New Member

    Jun 12, 2011
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    Hi All,
    Thanks for all your answers and input - very interesting.
    To have as much knowledge of electricity as possible is good!!!
    Thanks again
    Steve
     
  14. someonesdad

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    Decades ago I was in a physics lab alone late one night poking around in some circuitry I shouldn't have been poking around in. I hit something with my finger, then it knocked me for a loop. The next thing I remember is hearing a big bang and I was laying on my back looking up at the lights. The bang I heard was the big lab table hitting the ground after my legs jerked up in a spasm, lifting the whole thing off the ground.

    I had two truly epic bruises on the tops of my thighs. Of course, that was a lesson I never, never forgot and turned me into a bit of a safety Nazi...
     
  15. strantor

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    I can't attest to this specific story per se, but I have witnessed Navy Nuclear Electricians Mates (supposedly the smartest people in the navy) taking turns shocking eachother with a megger. There was a memo issued on this specific issue, so I assume there was an incident. I wouldn't be too surprised to hear that one died at the probes of a megger, and a megger could easily turn into a DMM through a few retellings of the story.
     
  16. JoeJester

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    Apr 26, 2005
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    If there was a death due to multimeter, there would be a mishap report and the subsequent all hands training about doing stupid things.

    Have you heard of people testing 9V batteries with their tongue? I would say the resistance of the tongue is much lower than between the fingers.

    Remember, know what your doing because the a$$ you save may be your own. Otherwise, do the world a favor and write your own submission for a Darwin Award.
     
    Last edited: Jun 18, 2011
  17. Wendy

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    Tongue testing goes toward current path. If you induce a current between both hands it will go through the heart. This is why you will hear people talking about one hand in the pocket. I don't do it myself, I just pay close attention where my hands are, but I understand the logic.

    I think most folks can come up with really stupid stuff they have done. I know I can, like the time I was groping blind for the water cut off inside an old laser after it sprung a major leak, knowing there was a couple of farads within a foot charged to 300VDC. It may not have killed me, but I suspect I would have been nicknamed Lefty if I had screwed up.
     
  18. NickNYC

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    Jun 30, 2011
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    A static electricity shock flowing from your feet, through you into a doorknob, and then into ground, is thousands of volts, but at microamps.

    If 10 amps flowed through you at the same voltage as a static shock, you'd be bacon. Jack Nicholson would be leering at you yelling "I'm glad you're dead!" So it's generally true that it's the amperage that's dangerous.

    Another way to look at it is if someone throws a BB at your head, and then someone throws a brick at your head with the same force. Not hard to figure out what's going to cause more damage.
     
    Last edited: Jul 3, 2011
  19. MrChips

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    Oct 2, 2009
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    I come from the "one hand in the pocket" school. I will generally do this whenever I am poking around anything over 50V.
     
  20. monster_catfish

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    Mar 17, 2011
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    I have a follow up question about the risk of electric shock while soldering. Is there any potential at all for faulty soldering iron held in one hand, and bare solder wire held in the other, to send current through the heart ?

    I was so troubled by that thought that I held the solder wire with a thick glove when I recently started doing solder work for the first time in a good while.
     
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