Electrical safety

Uh, I think I should point out that it is the amperage of a current going through your heart that will kill you, rather than the voltage per se, and getting that amperage through your heart depends both on the source voltage and the resistance to the applied voltage. Usually, 12-volts does not penetrate the skin and will not kill you. However, if you cut your hand and the voltage is applied directly to your bloodstream, the saline solution of the blood is a very good conductor and I believe it is possible to get sufficient current across the heart to interfere with it and potentially kill you. As the voltage increases, the amount of resistance to prevent lethal current flows also increases (Ohm’s Law). So a spark plug circuit generating 40,000 volts penetrates the skin quite readily, and then survival may depend on the exact path of the current takes to ground and the maximum amount of current available from the ignition system.