The fires burned out of control during the afternoon, causing floor beams near column 79 to expand and push a key girder off its seat, triggering the floors to fail around column 79 on Floors 8 to 14. With a loss of lateral support across nine floors, column 79 buckled – pulling the east penthouse and nearby columns down with it. With the buckling of these critical columns, the collapse then progressed east-to-west across the core, ultimately overloading the perimeter support, which buckled between Floors 7 and 17, causing the remaining portion of the building above to fall downward as a single unit. The fires, which were fueled by office contents and burned for 7 hours, along with the lack of water, were the key reasons for the collapse.