Once was Mortimer wrote:I might have to reread it, I thought characters could leave a death zone, just at the risk of a free attack.
As it turns out, I misquoted. If you walk into a death zone, you have to stop moving there, but can leave the death zone normally on your next turn. I didn't see anything in the rules about attacks of opportunity, but I might have missed them so I won't comment one way or the other on that. (Source is slev's March 2015 rewrite of the rules)