I pop popcorn in brown lunch bags (no water) all of the time, and I've never had a problem with it (I've always had really super-cheap low wattage microwaves).
I read in a magazine that it wasn't safe to pop popcorn this way, because the bag could catch fire, but since it had never happened to me, I really didn't think it was a big deal (besides, a fire IN a microwave is pretty easy to contain - just don't open the door until the fire runs out of oxygen and puts itself out).
So anyway, one day I was at my parent's house, showing my mom how to make popcorn this way (in a more expensive, higher wattage microwave) and the bag burst into flames before the popcorn could pop. At least I kept my head, and convinced my mom the fire would put itself out and that we shouldn't try to pull the burning bag from the microwave.
Since the bag fire, I have been a bit more cautious about making popcorn in lunch bags. I still do it, but I stand in front of the microwave, watching the bag the entire time, so if there's any sign of burning I can turn the power off.
I'll have to try dampening the bag before popping, it'll give me a little extra assurance.
Last edited by kaplods; 10-05-2009 at 10:07 PM.