The firemen would NOT have been considering that the building would fall. That was a great shock to the structural engineers, authorities, etc..... that the building would fail so quickly.
YES, they knew the buildings might partially collapse after some time and might later fail, but they did NOT go in there in the knowledge of what was going to happen. AND, as firemen they would have known that even with their training things could go wrong in a burning, damaged building which could kill them - they knew they were, yet again, putting themselves at risk.
HAVING SAID THAT, all firemen risk their lives on a daily basis, and almost everyone has a great fear of death by fire (actually normally asphixiation) - I certainly do. I would find it very difficult to do that job, even though I know that today's training is very strict.
The US have grasped hold of the "heroic" aspect of the firemen (and police) because they want to take something positive away from the tradgedy. It's not exactly propaganda, more a need for reassurance, but it is not totally honest.