I used to work in a high voltage laboratory, and we
routinely had safety presentations. In one such event
we had a presentation from an EE who had a lot of
experience studying high voltage, getting zapped, and
the like. A few points remain with me.
One was that an electrical model of the human body is
a leather bag filled with salt water. The resistance
of the skin (leather) can be high when dry, but drops
by orders of magnitude when it get wet. Ions in the
skin go into solution. Below the skin the resistance
is very low (blood, organs etc). If the skin is
breached, a voltage well below 100 volts can produce
lethal currents.
Another point is that the breakdown voltage of dry
skin is of the order of 600 volts. This number varies
with moisture and the part of the body. If you get
your body across potentials of this size, the current
flashes through the skin and you get fried. One
poster mentioned a experiment on himself with a
variac. This is very dangerous because if the thin
skin breaks down at the point of contact with the
electrodes, the current will increase tremendously
because the low resistance of the body's interior.
Another point I found interesting is that some people
survive brush very high voltages (like 100kV) because
they draw an arc inches before they actually touch the
conductor. With luck the muscular contractions push
the victim away from the danger rather then into it.
Working with the stuff made very respectful of what it
could do. I witnessed one serious accident in which a
technician got burned when he opened the 27.5 kV
primary blades of one of the transformers in our
substation. The transformer was loaded, and the back
EMF resulted in a huge arc which exploded the big,
gray switch enclosure. The technician went flying
through the air, but he thankfully survived.
Matt Jusinski, Morris Knolls HS, Rockaway, NJ
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