I've been looking everywhere for this, but I can't seem to find a definitive answer. Does anyone know how long someone would have to be exposed to an electric shock of average voltage for it to kill them?
Wiki is your friend here. There are other factors noted like skin resistance, dry vs wet. Then of course there is whether or not you are grounded and will the volts go around you or through you. Shocking a heart back into gear you use 300 joules and if that fails you go up to 400. There's an incredible picture in the Wiki link of the burn pattern on a guy's back who survived a lightning strike. This source also looks useful: Ohm's Law.
It's also a case of what you mean by kill. The majority of deaths by electrocution are likely death by cardiac arrest caused by electrocution. From what I remember, it only takes a very small current across the heart (electrically speaking, there is an electrical split across the body from right shoulder to bottom left ribcage), something in the order of milliamps IIRC. There is also the other end of the spectrum and I'm unfortunate enough to have seen a few video clips of this. Persons messing around with cables carrying high voltages and currents and BAM, big flash and they are dead as a dodo, in one case the poor guy caught fire as his body fat combusted. Nasty.
A young healthy heart will restart itself quite often after an electric shock. I've seen it happen in the OR during open heart surgery. You shock the heart to stop it (technically it causes the heart muscle cells to contract willy nilly rather than in unison, aka fibrillation) and sometimes the pacemaker node just gets things going again. Death from electrocution is more akin to burning to death, but the burns are on the inside rather than the outside. Medical aspects of electrocution
I'm a journeyman electrician. Happily, I've never seen anyone die, although I have seen someone knocked across a room and temporarily blinded. In the early part of my career, I've been shocked more than a few times. I once carried a scar on my finger that lasted years, and as GingerCoffee mentioned, it burns from the inside out, so I had to let the skin and the scar naturally rise to the surface before the scar disappeared. Here in the US, the common household voltage is 120volts (for ceiling lights, and appliances and/or lights that you might plug in) and 220volts (for big appliances like the AC and ovens, etc.) 120volts tends to grab hold of you and won't let go - it feels kind of like the feeling you get after you stand on a foot that has gone to sleep, except far more intense, and this is caused by the rapid on and off of an alternating current. Either the weight of your body pulls you away from the source of the shock, as your muscles contract, or somebody kicks you away. 220volts tends to explode like a firecracker - this is how I was scarred - it doesn't necessarily grab you, but it can. Higher voltages like 277 and 480 volt explode with greater power respectively, and they are found in stores and other business environments. When I place a wirenut over live wires at this voltage I can usually hear it crackle. The lower the voltage, while at the same time, the higher the amperage the more the shock will grab and expose you to the electrical current rather than explode and possibly take a body part with it. (I don't want to get into cross phasing which can occur in voltages higher than 120, because it's difficult to explain without diagramming it, but it doesn't mean that what I'm about to say is any less true, so usually) what happens when you get shocked is that electricity is taking a short cut through your body to a ground (either the actual ground or something conductive that will take it to the nearest path to ground). So, if one hand is holding a live wire while the other hand is touching something grounded, the electricity while travel through your upper torso (including your heart.) A bird can land on a bare high power line (I'm talking 10,000 volts, or more) and not feel a thing because it, typically, cannot also be touching something grounded. Your question, how much does it take to kill is really dependent on amperage far more than voltage. With a single 120v light bulb activated, the shock won't hurt that much and won't grab that much (of course, experience has a lot to do with my assessment - common sense should tell you, don't try this at home!!!), but when there are several activated lights on the same circuit, it becomes far more dangerous. Anyway, I'm rambling, so this concludes Electrocution 101. I hope, at least, that this has been food for thought.
A guy at work dropped a piece of metal on a power lead & as he went to touch that piece of metal he was shocked which made his arm/body sore for a day or two - he had barely touched that piece of metal before he threw his hand away from it. Though i'm sure if you dropped a hairdryer in your bath that same 240volts would kill you.
