James,
> for all intents and purposes random - the frequency/phase difference
> between
> your relevant internal signals and the AC frequency.  That is to say that
> even a very brief shock with just the wrong timing could be the end of a
> person, even after he/she has sustained a much larger and otherwise
> identical shock due to subtle differences in the way that the 50 or 60Hz
> interacts with your body's signals.
>
> I am the first to admit that I have no hard evidence to back up this
> theory,
> but for my purposes I don't need any.

You are exactly correct - defribilators ("Clear!") basically work on this
principal. It is not simply a case of passing a large current through
somones chest, it has to be at exacly the right time in order to
stop/start the heart. Defrib units monitor the persons arrythmic heartbeat
and apply the shock at the right time. A shock from such a unit generally
lasts between 7 ms and 12 ms
  corresponding to a frequency range of 70Hz to 40Hz - congratulations to
whoever thought 50/60Hz was a nice frequency for mains electrity. The
response of your nerves varies greatly with frequency - below about 10Hz
or above 500Hz sensation of shock is vastly reduced.

There is no such thing as being accustomed to electric shocks, having
surived a shock before makes no difference, some people may however have
undiagonsed heart conditions which would make them more likley to die from
a given shock.

As regards the 9v batteries - are you sure people didn't die by testing
them with their tongue whilst operating heavy machinery / tightrope
walking / driving etc. i am quite sure that the tiny locallised dc current
is not enough to be dangerous even to people with heart conditions.

Regards

Alex Rice

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