I'm not in any way a safety expert, as well. But this argument caught my eye. So I asked my brother who is a fire fighter. Fire exits are, in general, supposed to open outwards. Regarding blocking, according to him, there is a reason why when you look at any properly made fire exit, there is nothing heavy hovering above it.

Now as for the door knobs, most fire exits don't have the normal door handles. Like in cinemas and theaters, there's this small slot where you can place your hand. For larger buildings though, there are bigger handles shaped like a hook.