I didn't know this for sure, but within the show does it just stun or kill on contact? That's the only thing I'm lost on in the show

Most likely

Well, she hit Iroh in the front, sideish...kinda..and he was fine it was almost at his lung I think o:

she didnt strike iroh with a lightning, it was just a blue fireball

most cases in real life kill the people who have been hit by lightning soo yes, its either he died or he went into instant coma

In the case of death it can happen.?? Just think about Iroh's redirection of lightning technique.?? He told Zuko to channel the energy through his stomach and then out the other arm.?? He then said to never let it pass through his heart or the results will be fatal.??

So think about this, if it hits the heart then it causes the heart to stop.?? So in the hospital they use paddles when your heart stops to try and revive you.??

Same concept.

It wouldn't be a very good ultimate technique if it wasn't a sure thing! On a more serious note however, lightning would most likely be instantly fatal. The lightning burn hit aang on the spinal cord high on the back, then grounded out through his left foot, you can see the burn on the bottom. That means in addition to absolutely ravaging his central nervous syste, (which incidentally would have caused him to loose bowel and bladder control as well as cause continued incontinence if he live) it burned everything on the path through his viscera out through his femoral artery and out his leg. The damage would be massive and for the most part unsurvivable. Of course its a matter of voltage and amperage. Iroh was hit by blue fire.

So,??maybe that lightning stopped Aang's heart, but the spirit??oasis water started it up again...like a defibrillator....

i thought it was blue fire, not lightning...

In the show context, we really do not know how powerful it is. Real lightning is extremely powerful, but I seriously doubt if the lightning the Firebender's wield is as powerful as the real thing. Though people have been struck by lightning multiple times and lived. Cant be good for the health, though

PEople that survive high energy burns do so because circumstances conspired to allow the lightning to pass through them, much like Iroh describes, without crossing or dwelling in vital areas. If a person was to absorb the energy of a lightning bolt that had no where to go they would literally explode into a fine mist burned to ash by the torrent of power. However by being a good conductor you avoid the heat buildup and only suffer minor damages, save when it screws with the CNS.

Don't forget that if you know the technique you can reflect the lightning bolt just like iroh did in some episode.

huh, those are all pretty good answers (especially the one about the Central Nervous System)

It probably depends just like fire.
If you get hit in the vital spot, you will most likely die.
However, if it hits you on the finger, I doubt it will kill you.