Name: Charles B.
What equations do I use to find out the resistance of the
human body to electricity, and further how would I go about solving how
much current is needed to kill a human? I know the answer to the second
part is .07 Amps but how do we get that figure?
If you are considering only DC electricity, the kind from a car battery, the
formula for resistance is voltage across the body divided by resulting
current through the body. Because the body is so big, however, it depends
on where you attach the electrodes.
If the electricity flows from the thumb to the pinky of the same hand, only
the flesh of one hand is affected. Resistance will be fairly small. The
hand will burn before the person can be killed. If the electricity flows
from one hand to the other, the electricity has to flow through more flesh.
Resistance will be greater. Most of the electricity will flow near or
through the heart. It is very likely that the person will experience heart
failure. A current of .07 Amps is enough to cause this. The number comes
from experience, not calculations.
There is no formula for exactly how much current will kill a person. Every
body is built a little different. We can only know an average value. Any
electrician will tell you not to worry about that value. When working with
electricity, it is best to prevent it from flowing anywhere beyond one hand.
A small amount of electricity in the brain can kill you. If not enough for
death, it can damage the brain or at least cause an extreme siezure.
Electricity through the heart can stop the rhythm, preventing the blood from
flowing correctly. This is the most common cause of death due to
electricity. Keep one hand in your back pocket, or strapped behind your
back. Never use both hands when more than just a few flashlight batteries
Dr. Ken Mellendorf
Illinois Central College
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Update: June 2012