Just prior to the impact there were three firemen on the helipad at the Pentagon. The president was supposed to land at the helipad two hours after the impact, and so they had just pulled the foam truck out of the firehouse and were standing there when they looked up and saw the plane coming over the Navy Annex building.
They turned and ran, and at the point of impact were partially shielded by their fire truck from the flying debris of shrapnel and flames. They were knocked to the ground by the concussion, were able to get up, go over to the fire truck, and initially they were able to get it started to call for help at Fort Myer. And then they had to put out parts of their uniform--their bunker gear was actually on fire, so the first thing they had to do was put out their own fire truck and their fire equipment and they tried to start the truck and move it, but they discovered that it wouldn't move.
They got out and looked, and the whole back of the fire truck had melted. So they turned their attention to trying to rescue people from the building and went over and helped people escape from the building.