What combination of voltage and current is most dangerous

Discussion in 'General Science' started by Niles, Apr 6, 2009.

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  1. Niles

    Thread Starter Active Member

    Nov 23, 2008
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    Hi all.

    I've thought about this issue for some time now: What combination (i.e. high or low) of voltage and current is the most dangerous (i.e. is most likely to kill an average-sized person)?

    Best regards,
    Niles.
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    That varies widely, what severely injures one person can be a tickling shock to another.

    Anything over 50V @>10mA potentially could kill.


    The electric chair used 2000 Volts/5 Amps for 15 seconds. More than one cycle was applied(up to three). Some condemned men received three cycles, and survived to file lawsuits that their sentence was carried out, and it wasn't their fault if they weren't dead.

    So, the question is only possible to answer in terms of "What is safe", which varies, especially if known or unknown medical conditions exist.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    There is no absolutely clear answer. Although the current capability of the circuit has little to do with it. Only the voltage present can present a shock hazard.

    It is the voltage between two points of your body that causes shock. The voltage difference can cause a current under the skin that affects your muscles. If it's between your elbow and a finger, it can be painful. If the current path includes your heart, it can be fatal.

    As dry skin conducts much less that wet, the amount of voltage that can cause fatal currents through your body varies. 12 volt circuits are supposed to be non-hazardous, but I have managed to get a good jolt from an automobile wiring harness when a stiff strand that was part of power wiring broke. I managed to catch the curled wire (fishhook in electronic terms) with a finger. I had my arm braced in some part that was part of the chassis, and so got a really unpleasant tingle from it. That was because part of the 12 volt conductor was poked through my skin.

    To be safe, consider that any voltage can cause lethal current through your chest. Always assume exposed wires are hot, and verify their electrical state with a meter before making contact with your skin. Never assume shoes or clothing to be effective insulation.
     
  4. Niles

    Thread Starter Active Member

    Nov 23, 2008
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    Does the current travel "across" the skin or inside the arm (or torso)? And where does the free charges come from?
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    Your skin is more of an insulator than inner tissues. Current path is hard to define. Some electric shocks are felt as a spasm of the whole arm or leg. High frequency high voltage can result in a couple of black holes in your palm, with a discernible carbonized track under the skin joining the holes. The burn path was not straight, though.

    That RF burn was off a damper diode in an old tv - not likely to be a problem today.

    Other people have contacted power lines and suffered primarily surface burns.

    The point is that any potential shock hazard must be treated as if it had the capability of causing fatal injury.

    I don't understand your question about "free charges".
     
  6. Niles

    Thread Starter Active Member

    Nov 23, 2008
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    When there is a potential difference (i.e. a voltage), then where are the free charges drawn from?
     
  7. b.shahvir

    Active Member

    Jan 6, 2009
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    The free charges (free electrons) already exist in your body, naturally. The external applied potential difference (voltage) only pushes them into motion which is called elecrtic current.

    This is analogous to a pump driving water current around a closed pipe circuit. The water is somehow considered to be already present within the pipe circuit.
     
  8. Niles

    Thread Starter Active Member

    Nov 23, 2008
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    Ahh, I see. Thanks!
     
  9. ethan007

    Member

    May 11, 2009
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    Hey it is really a good thing to read about thank you.
     
  10. mik3

    Senior Member

    Feb 4, 2008
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    I don't agree with that. If you have a 1000V source for example which can deliver only 1uA then you won't get shocked.

    It is the amount of current and the frequency of the source which matters.
     
  11. DonQ

    Active Member

    May 6, 2009
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    Of course, when you connect the "1000V source" to your body, the voltage will drop because it can only supply 1μA. Your body has become part of a voltage divider. Just because a 10MΩ meter says 1000V doesn't mean that a 10kΩ body will register the same voltage.

    Bottom line is that it is the current that will kill you, but it takes voltage to push that current through you. As little as 1mA supplied directly to the heart will kill you, but it takes more than that supplied to the hands for the part that winds up going through your heart to equal 1mA.

    Callused hands, long arms, large body, body hydration, body fat and sweaty palms are all things that are involved on how much voltage it takes to push this current through your heart.

    Of course, we hope the real question is "How much voltage/current does it take to really piss you off?!" From experience, it must be less than it takes to kill you!:D
     
  12. b.shahvir

    Active Member

    Jan 6, 2009
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    very true!......and of special concern since you are still alive after that. ;)
    Cheers.
     
  13. thingmaker3

    Retired Moderator

    May 16, 2005
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    Whoever says it can deliver only 1uA gets to stick their tongue on it before I will! I won't even go first at Van de Graaff demonstrations. :cool:
     
  14. b.shahvir

    Active Member

    Jan 6, 2009
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    Oh yes! how can one ever overlook the sensory perceptions of various appendages of the human body. :D
     
  15. mik3

    Senior Member

    Feb 4, 2008
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    I am just saying. :p
     
  16. PRS

    Well-Known Member

    Aug 24, 2008
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    I'm surprised no one has brought up the frequency quesion. This was a raging issue before the turn of the 20th century. Edison championed DC as being safer while Westinghouse championed AC as being safer. Personally, I think Edison was right.
     
  17. rvh002@gmail.com

    Active Member

    May 15, 2009
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    Be very carefull with statements like that. Most of the above is true, but I can add that a capacitor charged to 1000v can be lethal when discharged through the normal human body. (Frequency is not important)
     
  18. Renesis

    New Member

    Jul 14, 2009
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    Time also matters. The risk of cardiac arrest increases greatly at long exposure times. If you grip a live wire with your hand, muscular contraptions may prevent you from letting go, witch is a very dangerous situation.

    Frequencies can matter. You may not feal pain from high freq currents, 20kHz+, witch is potentially dangerous. Imagine being shocked without even being aware of it. This is why many people think Tesla Coil streamers are safe, witch is not true. Horrible RF burns and tissue damage could be the result.

    Also, at fast risetimes and frequensies far into the MHz range, skin effect comes into consideration. High frequency currents tend to stick to the surface of conductors, while the core current is far less. This is believed to be a partial reason why people can survive direct lightning strikes, and still be perfectly able to kill themselves on their house mains. Lightning has a very fast risetime, in the order of 40 kA/ms.

    http://en.wikipedia.org/wiki/Skin_effect
    http://en.wikipedia.org/wiki/Lightning
    http://en.wikipedia.org/wiki/Tesla_coil#The_.27skin_effect.27_and_high_frequency_electrical_safety

    On the subject of lightning, one big survivability factor is actually wet clothes. Wet clothing from rain may route the bulk of the current outside the body, and in some cases leave the victim unharmed.


    But the most common electricity-related injuries are physical injuries, as the shock often makes the victim fall or bang into something, or say very, very bad words:D
     
  19. b.shahvir

    Active Member

    Jan 6, 2009
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    Your post is very "Enlightning"...thanx ;)
     
  20. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    It would seem that wet clothing would provide a path to ground. Some advice on avoiding injury suggest the opposite, that is, insulating oneself from ground.

    Can you provide some reference for the wet clothing theory or was that based on theory?

    John
     
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