When I was in apprenticeship, they taught us that 50 milliamps was enough to stop your heart. When I quoted that the other day, an engineer corrected me by saying that it was 5 milliamps. We both volunteered our confidence in our figures, so I was wondering if the figure had changed.

I was always taught that 100 mA would do you in. Here is a link to a website that talks about the effects of current on the heart.

http://www.tpub.com/neets/book2/5j.htm

It is dependent of the body's resistance and the voltage (determines amperage) and the level of luck the victim has. This is why some die from the slightest shocks and others get the snot shockout of them and live.

A lot depends on the path through the body. A shot down your leg hip to foot is not nearly as dangerous as one from hand to hand or directly into your chest (the reason pool lights need to be 18" underwater).
Of course a small shot through one finger can kill you if you fall off the ladder.

You do not even need to be shocked. You can be the unlucky one at the bottom of the ladder when the sparked sparkie gets it in the finger...

5ma will not stop your heart. 5ma is "safe", which is why GFCI is set to not allow any more than that.

Just like radiation levels, there is no actual current level that is garunteed to kill you- but at somewhere around 20-100ma through your heart, it will stop beating properly. In this range, muscle action is also inhibited, preventing the victim from escaping the shock.

FYI, there was a man once killed himself with a 9V battery during a classroom exercise. He pierced his skin with the ohmeter probes, lower the contact resistance to the point where he recieved a lethal shock through his heart. It does not take much!

"one hand rule", anyone?

5mA is generally considered the 'annoying shock' level, where you feel it, but no real harm results. As others have mentioned, nothing is certain in this world.

The electrocution I witnessed - breathing and heart stopped cold, WAS able to re-start manually - was almost certainly at a very low current level. The current exited the mans' temple ... apparently causing the brain to shut down. This path would call for much less current that 'through the heart.' Through means not quite understood by medicine, the body actually does a pretty good job of directing current around the heart.

Not to be a doubting Thomas here, does anyone have any actual info on the 9volt battery story? I do believe it is and urban myth but I am not sure. I could go to these sites like snoops.com (I think that it is what it is called) but It would take away from my time here.

I'm skeptical too, but I swear I read at as confirmed on snopes... Can't seem to find it, though, and Darwin considers it "unconfirmed", which probably means "********":
http://www.darwinawards.com/darwin/darwin1999-50.html

Well, the math is reasonable and it's completely plausible, like something one of us would do in a lab. I would not try this at home.

I believe it was a USN sailor in electricians Mate "A" school. I think it was after learning about "internal resistance" with respect to batteries.

Larry C