The fiberglass stuff is only dangerous if you're in contact with it and you
don't wear a breather mask. And, if you need to be in INTIMATE contact with
it, like moving it out of the way to run wires or something, you should plan
on dumping your clothes into the washing machine with COLD WATER immediately
afterward. Don't go laying around on the furniture in those clothes.

But, properly selected and installed, it's not a problem.