I managed to shock myself and wanted to see how dangerous that shock actually was to me (to figure out how much of an idiot I was). So I looked around for information on how to 'calculate' the various electricity related figures (mainly voltage and amperage) and at this point I'm more confused now than I was when I started…
I often came across the "it isn't the voltage that kills you, it's the amps" quote, but it seems quite clear that the statement isn't really true from what I've seen:
A car battery (low voltage high amps) won't kill you because the voltage is very low and won't 'penetrate' the skin, a taser (high voltage low amps) also won't kill you because despite the high voltage and amps are so low that it won't do much real damage, and even a high voltage high amp device may not kill you if the 'exposure period' is small enough…
So I've got no good idea on how to 'judge how dangerous a shock can be' aside from knowing it involves time, voltage, and amperage in relation to each other. Amperage seems especially confusing to me because usually people throw out the I=V/R formula to estimate how many 'amps your body experienced', but this formula only seems to consider the voltage of the source, since a source with 12 volts / 1 amp and 12 volts / 1k amps would work out to be the same (I'm sure that my usage of this formula is wrong…).
So voltage won't outright kill you and amperage won't either (well, not without extreme values), so what is a formula that can actually approximate the risk? Does it involve watts perhaps?
*A little more info since Rod Vance asked for it: while I was moving a circuit board I adjusted it a bit in my hands and I think when doing so my thumb touched the terminals of a Capacitor and I got a bit of a 'buzzing sensation' (220V/300uF specs). Nothing major (hopefully)…
Best Answer
This question is very complex and any complete answer would probably need to be book sized. There are many effects of electricity on the body and they all play a role in how dangerous any shock is. As others have noted, the important factor is current. However, besides intensity, frequency,duration and location are important. Also, a current that goes straight through a finger will hurt a lot, but be much less dangerous than one that goes through the heart.
Regarding the main effects of current on the body, they can be divided in thermal and non-thermal effects. Thermal effects mean that due to the resistance of the tissues through which the current flow, the tissues heat up and are eventually damaged. Watts, as mentioned in the OP is very important in this type of effects. Non-thermal effects are due to disturbance of the body's function through interaction with cells that normally respond to electrical currents, the nerves and muscles (the heart is a muscle also!). This is where it gets complicated.
There have been accounts of people on the electric chair surviving a first shock, but in which the current caused all muscles to contract so violently that bones were broken. Also, while a shock can send you in fibrillation, a defibrillator uses a carefully shaped shock to reinstate normal heart beating. While you would think that passing a current through the brain would not be a good idea, that is exactly what electroshock therapy does. Of course, this last one was abused, but my understanding is that in some cases, it's the only thing that remotely works for some patients. So, the effect of a specific accidental shock will be highly context dependent.
Another important factor in electrical shock is skin resistance. An intact dry skin has much larger resistance than a cut skin. For a given voltage, intact skin will allow a much smaller current to flow through the body than injured or wet skin.
Regarding the difference between voltage/amperage, one has to be very careful. A car battery can provide a very large amperage if required, but the voltage is still only 12 Volts. If you insert a large resistance between the terminals of the battery, the battery will not suddenly provide 100 amps because it can. Voltage is the same. You may have a very large voltage, but not enough charge to provide a large current. To get damage from an electrical shock, you need enough voltage to create a sufficient current through the body, and capacity to provide that current for enough time.