Accident Investigation Question

Discussion in 'General Electronics Chat' started by Tabsan, Apr 18, 2012.

  1. Tabsan

    Thread Starter New Member

    Apr 18, 2012
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    Hello,

    Whilst I am aware of the US Navy 9 volt tester fatality (myth or not, I'm still unsure) I have a question about low voltage high current incidents.

    We have a person reporting a shock which led to unconsciouness from a 9 volt 2.25 Amp DC source.

    Reportedly leaning on the exposed wiring with his forearm.

    This is being refuted by company electricians - but I am investigating and I am minded to believe his claim.

    I know 99mA can lead to serious issues, but could he have received a shock at all?

    Thanks in advance.
    Tabs
     
  2. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    It would be difficult to get a shock from 9 volts, but there are a lot of variables that come into play. Things like humidity and dampness of the skin could make it easier to receive a shock.

    99mA is more than enough current to do serious damage. 30mA is enough to kill, 15 if it's held wrong, but it's fairly uncommon.

    I really don't know about the 9v shock. It seems a little iffy, if you ask me, but I'll let some other members chime in here too, with their opinions.
     
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  3. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I posit that in order to be electrocuted by 9V, probes would have to be deliberately inserted under the skin in strategic locations. The resistance of skin is high enough that 9V would not generate enough current through the body to to notice any effect. However, if the skin were wet, the resistance would go down. I've heard that if you are incredibly sweaty and you contact both terminals of a 12V car battery, you can receive a shock. If the person were incredibly sweaty and leaned a forearm across 9V terminals it is possible he felt it, but I seriously doubt that it would cause unconsciousness.
     
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  4. t06afre

    AAC Fanatic!

    May 11, 2009
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    Given that the 9 volt DC source worked as it should. I will rule out any shock leading to unconsciouness from the latter DC source. Even with open wounds on each arm. And the DC source connected directly into the wounds. It would not hurt you. Try to lick on a 9 volt battery, and see what will happen. You will some tickling in your tongue. But nothing more
     
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  5. Tabsan

    Thread Starter New Member

    Apr 18, 2012
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    I forgot to say this was below a sink, against a copper waste pipe. It is feasible that the injured person was sweaty, as it is also feasible the condensation was present on the waste pipe.

    Thanks
    Tabs
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    My college physics professor once related a story to us about the time he was testing some inductors for continuity with a battery and a lamp. He touched everything together, saw the lamp light and concluded he has a good inductor. Then when he broke the connection he received a significant shock!

    It took him several minutes to recover, but not believing this was possible he repeated the experiment with the same results.

    He eventually discovered the principle of inductive kickback.

    "If the fool would persist in his folly he would become wise" - William Blake
     
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  7. t06afre

    AAC Fanatic!

    May 11, 2009
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    In remember I had a ground fault in my house. So I was zapped for example then I was taking a shower and adjusted the water. It was highly unpleasant but not enough to knock me out. I would rather investigate on that path. If the person is telling the truth something must have happen.
     
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  8. strantor

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    A 9V battery has significant internal resistance and cannot output more than milliamps. I am curious what would happen in you licked a 9V lead acid car battery (if such thing existed).
     
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  9. DerStrom8

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    My guess is you wouldn't have a tongue after that :eek:
     
  10. Tabsan

    Thread Starter New Member

    Apr 18, 2012
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    This was a 240 volt AC to multi volt DC (adjustable between 3v; 4.5v; 5v; 6v; 7.5v, 9v, 12v --- 2250mA 27VA)

    Mains over here is 240 volt.

    Thanks
     
  11. t06afre

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    Given that my tongue did not had any open wounds. It would not matter much as long as the source was 9 volt.
     
  12. DerStrom8

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    As strantor said, a 9 volt battery can not source nearly as much current as a lead acid car battery can. Licking a 9 volt battery won't cause more than a couple of milliamps to flow through your tongue. Licking a car battery could easily allow a lot more current to flow, and thus cause a lot more damage.
     
  13. strantor

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    right; I got hypothetical for a second, sorry. I would expect that if you connected a 9V 2.25A DC power supply to your tongue, it would hurt significantly more than if you connected a 9V battery to your tongue. I still think the guy's story is a lie, but I'm only 95% sure.
     
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  14. vpoko

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    Jan 5, 2012
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    Are you sure about this? I haven't tested a 9V (and am not at home now to check), but my DMM has shown me, if I recall, 6 amps from a single AA battery.
     
  15. atferrari

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    As far as I know, some 9V batteries that were given to me (I was maybe 10 or 12 yo) were more or less exhausted but enough to produce a sensible effect when touching both terminals with my tongue.

    I recall seen some "flashy" effect with one of them. That made me to stop such a stupid game.

    Every time, aftertaste was awful.

    Silly me.
     
  16. t06afre

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    Even on a wet tongue. The DC resistance of the skin will be a few Kohm. Hence the current will be limited. And ohms law will still apply....DoH!
     
  17. DerStrom8

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    Touching the probes directly to the terminals of a 9-volt battery is not an accurate measurement. The meter has a low internal resistance, so you'd be getting, effectively, the short-circuit current of the battery. That is completely different from connecting the battery to an actual load.
     
  18. vpoko

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    Jan 5, 2012
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    I understand, I was just pointing out that the internal resistance of the battery alone isn't enough to limit the current to the milliamps range. I found that out the hard way when I blew a fuse on my DMM thinking that there's no way a AA battery would put out more than 200mA.
     
  19. t06afre

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    A shock powerful enough to knock you out. Would most probably also cause at least some first degree burn on the skin. Did this person report anything like this at all.
     
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  20. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    has your investigation determined the current path?
     
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