# Can the smallest electric shock kill you?

papertiger-
well you could get someone through the skin too, but that would have to be a higher current shock to compensate for skin impedance. the same rule applies though: a smaller high-current shock could cause death through the skin if timed properly… i hope that makes sense.

Not so fast…!

The resistivity of human skin can vary wildly, depending on a person’s health, level of pysical activity, rest, and other factors. An extreme example would be someone dead-tired, ill, and soaked in sweat. The other extreme could be a well-rested, physically-fit person in very dry air. The Navy used 50k ohms as a basic level of human skin resistivity, but then the instructors showed me how easy it was to reduce that to as little as 1000 ohms, just by working up a really good sweat.

Bottom line: Don’t take any shock you can avoid.

I’m not talking about variances in skin resistance due to moisture, etc. I don’t want to stray too far into nitpick territory, but in EE 101 the first thing they teach you is that you use ohm’s law only when there is a proportional relationship between voltage and current. Not everything is “ohmic.”

The “equivalent resistance” of a human body varies with the voltage being applied. At very small voltages (like what you get out of an ohmmeter) it may be a few hundred k ohms. At a significantly larger voltage, the “equivalent resistance” of the human body drops to less than 1 k ohms.

If you are talking about instantaneous “resistance” where the resistance is a function of voltage and current, well, that always bothered me because that’s not at all what ohm’s law is all about. George was basically trying to say that in lots of materials the current and voltage varied proportionally. A varying R was not what he had in mind.

There is a handbook for isolated power systems (similar to the handbook for the national electric code). The intro has a good explanation of exactly what it takes to kill someone with electricity. It’s a good read for anyone interested in the subject, especially about the controversy in the early days of open heart surgery about whether or not tiny electric currents were killing patients. The outcome of this controversy was the red outlets that you see if you are unfortunate enough to end up in the hospital. These are special isolated power circuits designed to keep any fault currents to a maximum of 6 uA (if I recall correctly) as this is the largest amount of current that is thought to be “safe” if it passes through your chest cavity.