Electric Circuits – Which Electrons Kill You During Electrocution?

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I understand that there are three velocities in play in a circuit (I haven't studied Physics past high school so give me some rope)

  1. v1: the velocity by which the electrical field propagates through the conductor (equal to the speed of light)

  2. v2: the velocity of the free electrons in the wire. Free electrons move around randomly in a sort of Brownian motion at speeds in the order of 1000 Km /s. When no voltage is applied on the wire this random motion results in no aggregate movement of electrons.

  3. v3: a constituent velocity vector, consistent (not random) by which the free electrons move in the direction of the current. This is very small in the order of mm or even μm / s. This vector is added on the vectors of the "Brownian" motion and results in the actual flow of electrons.

My question is: when I am electrocuted which electrons actually kill me?

  1. electrons already existing inside my body that start to move under v3. This seems unlikely as they were previously moving at v2 with no harm. Also my body is not a conductor so free electrons inside my body don't make sense.
  2. electrons from the wire that pass into my body. Given that the additional speed they acquire because of the field is very small I don't see why they couldn't previously enter my body when I touched the wire (under no voltage). Also, v3 is very small so the experience of the electrocution in that scenario would have been that my finger is shocked first, then my hand, then my arm, then my shoulders. Instead an electric shock feels instantaneous.

And I haven't even considered yet that we are mostly using alternating current so no actual, net, flow of electrons into my body occurs. Can somebody clear this confusing mental model for me?

Best Answer

Which electrons kill you during electrocution ?

None of them. As you say, there are already plenty of electrons and ions moving around in your body anyway, so adding a few more makes no difference.

Death from electric shock is usually caused by the electric field, which disrupts the nerve signals which control the synchronised beating of the heart muscle. This causes ventricular fibrillation which prevents the heart from pumping blood around the body and leads to death within a few minutes if not treated.

And the usual treatment for ventricular fibrillation is to administer another carefully controlled electric shock from a defibrillator, which (bizarrely) disrupts the heart's rhythm even more severely, but then allows the body's natural pacemaker to re-establish the normal rhythm (if the patient is fortunate).

A very high voltage electric shock can have other serious effects - it can actually stop the heart completely or it can cause internal and external burns.

On the other hand, an electric shock that does not pass through the heart may have no ill effects at all. And the administration of electric shocks in a range of medical treatments called electrotherapy may even have benefits for certain health conditions.

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