getting zapped

[Ed Mellinger]

Hi Folks,

I work with 1600 volts on the deck of a ship, so I was motivated to do a
bit of reading about electrical safety.  Here's the gist of what I
learned.  I can provide further references if anyone's interested...
it's a bit off the EFI topic.

DISCLAIMER:  I'm forwarding this to the list as general background
material on an important subject.  It is based on my personal
interpretation of things I've read in the literature.  This material has
not been reviewed by any safety agency, is not guaranteed to be
accurate, and must not be used for design or other human safety
purposes.  'Nuff said.

[Intro stuff deleted]

"Though we speak of hazardous voltages, the real villain is current
forced through the body, and in particular through the heart, by the
voltage in question.  For a given voltage the current depends on the
skin resistance, which varies by orders of magnitude depending upon the
individual and the presence of water or perspiration.  The physiological
effects of current flow also vary, but typical examples are the
following:

                                             DC        AC	
threshold of perception	                      5   mA    1   mA
painful shock                                30         6
muscular control lost ("let-go threshold")   50        10
ventricular fibrillation (3 sec)            500       100."

"Since average skin resistance is between 1,000 and 10,000 ohms, it is
easy to see that any voltage over 100 V should be regarded as
potentially lethal, and 1600 V as almost instantly so.  According to the
literature there is very little middle ground in human shock cases:
there is either a temporary stunning effect and a great story to tell
later, or the heart stops beating and the victim is found dead."

Obviously your ignition's 25 kV will pretty much have its way in forcing
current through your body, but fortunately this multi-kV source is both
current and energy limited, to the extent that I've never heard of
anyone being electrocuted by their car.  BUT there's plenty of current
for involuntary muscle contraction, and as has been noted, if that
throws you into the fan or a v-belt, you could easily be hamburger
anyway.

Hope this is interesting... now go home and make sure the GFIs in your
garage work!

Ed Mellinger