Electronic – Why are typically fatal currents non-lethal when they pass through your body for a short time

safety

I've been reading up on electrical safety, and the commonly cited controversial quote "it's not the volts that kills you, it's the amps". What I have gotten out of these sources is that it is in fact the amperes that stop one's heart, but the voltage determines this current, and the body is a non-ohmic resistor. (I have read this which mentions a lot about the volts and amps).

However, I am confused as to how much time a current must be passed through your body in order to be fatal. This video states that if you were to model the human body as a 100 picofarad capacitor with a 1500 ohm resistor in series, a high voltage static shock would pass a very high current through the body, but for an extremely short time (less than a microsecond). How long would a potentially dangerous (>5mA) AC/DC current have to be passed through the body in order to harmful? I understand that this is maybe too general a question, but is it possible to give a figure accurate to a few orders of magnitude?

Also, if it is in fact the amperes delivered over time that are detrimental, would a unit such as the Coulomb be more suitable for determining how fatal an electric shock might be?

EDIT: I am assuming that the electric shock is delivered hand to hand where it is most likely to pass through the heart and thus heart fibrillation is of most concern. If there are other significant causes of death from hand to hand shocks that I have overlooked, please tell me.

Best Answer

You need to bear in mind that there are many different modes of damage possible,

  • Large current passed though tissue may burn the tissue
  • Modest current passed through a vital muscle (like that of the heart) may cause that muscle to operate in a manner that it's not used to and strain it so that it is damaged from the strain.
  • Very tiny current may interfere with the normal nerve signals that drive the heart's operation, throwing off the heart rhythm leading to ineffective pumping for long enough to be fatal.

So it's not a matter of stating a particular voltage, current, charge, energy or power. It's a matter of stating a range of very particular and quite different circumstances that pertain to different body systems.

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