NYC's Command Center Located on the 23rd floor of Building #7

Why did Giuliani set up a command post in another building when the twin towers were hit by airplanes?

To this day the government can't give a reasonable explanation of why WTC's Building # 7 fell like WTC 1 & 2 (Imploded and fell on it self) even though it was never hit by a plane and just had a few spot fires. No steel frame-building in the history of the world has ever fallen because of fire.