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Static electricity shock: Can it ever be lethal?

  1. Apr 16, 2015 #1

    rollingstein

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    I was wondering, is it possible to charge oneself with static to an extent that would be lethal or even damaging to a significant extent beyond the usual discomfort?

    What are the governing calculations? Instead of the usual carpets would any other materials in an exceedingly dry climate give rise to potentials where you could essentially self-shock to a greater extent?
     
  2. jcsd
  3. Apr 16, 2015 #2

    russ_watters

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    Yes. Have you seen the movie The Hunt for Red October? Helicopters generate a potentially lethal static charge.
     
  4. Apr 16, 2015 #3
    Sitting on top of a van de graff generator then jumping on to the floor would be definitely be unhealthy for you.
     
  5. Apr 16, 2015 #4

    sophiecentaur

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    "Unhealthy"???? Kids love to charge up on a School Van der Graaff and then discharge onto someone else or an earth connection. And Health and Safety doesn't get a mention in risk assessments.
    Of course, it depends upon the size of generator involved. They do make them with spheres of several metre diameter. The Capacitance (along with the final voltage - wrt Ground) will govern the charge stored. This link will tell you the capacitance of a sphere and you could take a final voltage of, perhaps, 500kV. Then use Q = CV
    The basic limitation of Capacitance of a simple sphere is pretty self limiting, I think.
    OTOH, an old fashioned Leyden Jar or a commercial high voltage 1μF capacitor would be more than capable of storing enough Oomph to spoil your day with only a modest few kV. You really need to be careful of those devils.
     
  6. Apr 16, 2015 #5
    Yeah I was thinking of the big impressive ones which can make 'lightning' which is several meters long.
     
  7. Apr 16, 2015 #6

    sophiecentaur

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    Yes. The numbers count though. I would hate for someone to get phobic about a little thing sitting on a lab bench.
     
  8. Apr 16, 2015 #7

    Svein

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    Remembering - 40 years ago I moonlighted as a medical instrument serviceman. One of the things I serviced was a heart defibrillator (a heart starter). It contained a capacitor (I seem to remember 8μF) which was charged to a fairly high voltage (at least some hundreds of volt) and then discharged across the chest of the patient. I did not see it in operation, but I am told the results were spectacular.
     
  9. Apr 16, 2015 #8

    rollingstein

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    Thanks. Well, obviously capacitors can kill. And so can Van de Graf generators I guess.

    My question was more along the line of what Russ Waters answered. i.e. an incidental side effect of another activity that leads to static charging.

    e.g. Say a large tank being filled up. etc. (earthing neglected)
     
  10. Apr 16, 2015 #9

    rollingstein

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    Ah yes, this one?

     
  11. Apr 16, 2015 #10

    anorlunda

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    If you're surrounded by explosive vapors, yes.

    But we should be able to calculate it. Wikipdedia says, "The Human Body Model for capacitance, as defined by the Electrostatic Discharge Association (ESDA) is a 100pF capacitor in series with a 1.5resistor[1]"

    Suppose we charged up the body to 1 million volts (very high). Then the charge will be 100 pf * 1 MV = 0.0001 columbs of charge. Now suppose we discharge all of that in one millisecond as a spark. The average current is 0.0001/0.001 = 0.1 ampere for 1 millisecond.


    On the subject of electrocution, Wikipedia says, "Death can occur from any shock that carries enough current to stop the heart. Low currents (70–700 mA) usually trigger fibrillation in the heart, which is reversible via defibrillator but can be fatal without help. Currents as low as 30 mA AC or 300-500 mA DC applied to the body surface can cause fibrillation. Large currents (> 1 A) cause permanent damage via burns, and cellular damage."

    So, on the basis of an order-of-magnitude estimate, yes it is possible to kill yourself this way. All you need is a megavolt voltage source in your house. On the other hand, that amount of shock is about 1/8 that of a defillibrator and (I think) approximately equal to that of a taser but for only one millisecond istead of seconds with a Taser zap. Both of those devices are considered non-lethal.
     
  12. Apr 16, 2015 #11

    rollingstein

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    Agreed. Static near a tank of, say, gasoline is a short road to another world.
     
  13. Apr 16, 2015 #12

    rollingstein

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    Nice calculation.

    But how do you calculate the other part? e.g. Walking on a carpet on a dry day charges you to how many volts? Is there a back-of-the-envelope way to estimate that?
     
  14. Apr 17, 2015 #13

    Baluncore

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    If you have a 100pF body, charged to 1MV relative to ground, the safety of the discharge will be dependent on the path taken by the discharge current. It is unlikely that significant current will flow through your heart on route to the ground. That usually only happens when your two arms close a circuit, or when current flows through an arm and then a leg to ground.

    The discharge path will be from a small patch of your surface / skin to some grounded object. Just prior to breakdown, charge will be moving towards the side of your body closest to the ground. Breakdown will actually begin with a corona discharge at a distance of about one metre. With 1 MV you can expect a flash burn over the area of skin near the discharge point. The energy released will be about 50 joule.

    Skydivers are subjected to the 30V/ft Earth potential gradient. A jump from 10,000 feet would represent a potential difference of 300kV. They do not get electrocuted on landing. Why?
     
  15. Apr 17, 2015 #14

    rollingstein

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    A gradual discharge as they descend?
     
  16. Apr 17, 2015 #15

    OmCheeto

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    I don't know that there is a back of envelope method, as there are lots of variables.

    It would be a fun experiment to do though.
    It looks like the components you need are sitting around the house, and on your head.
    You would want non-conducting materials from opposite ends of the following list:

    Hair and Teflon look like good choices.

    This is interesting:
     
  17. Apr 17, 2015 #16

    anorlunda

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    With respect to the lethality of sparks, the big problem is the difference between what is possible and what is probable.

    It may be true that someone could have their heart stopped by a tiny discharge. But past era designers of electric chairs found out that certainty of death can be very elusive.

    The lethality part of the question is not electrical engineering, it is biology.
     
  18. Apr 17, 2015 #17

    nsaspook

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  19. Apr 17, 2015 #18

    Baluncore

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    The two materials rubbed together would need to be connected to the body and to ground. If it required 1MV on a 100pF body to be lethal, then the insulation would need to be 1 metre thick to prevent corona breakdown through the surrounding air. But triboelectric materials are insulators so the triboelectric charge would not appear between the body and ground. So the air that you breathe protects you from self-inflicted electrocution by friction generated static. To generate a lethal charge you would need a capacitance significantly greater than the 100pF of a human body.
     
  20. Apr 17, 2015 #19

    rollingstein

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    What about the instrument to measure the voltage? After making my little brother walk across the linoleum for 6 hrs what do I measure him with?
     
  21. Apr 17, 2015 #20

    rollingstein

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    The median heart I guess.
     
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