NY Times Covers WTC-7 NIST Conference
The investigators determined that debris from the falling twin towers ignited fires on at least 10 floors at 7 World Trade Center, which was about 400 feet north of where the city’s two tallest buildings once stood. The blazes burned out of control for six hours, as the city fire department, devastated by the collapse of the twin towers, abandoned its efforts to extinguish the fire, and the sprinkler system was incapacitated.
The heat from these fires, the investigators said, caused the beams on the lower floors of the east side of the tower to expand, ultimately causing a girder on the 13th floor to disconnect from a critical interior column that supported the building’s long floor spans. Once the 13th floor gave way, a cascade of floor failures started down to the fifth floor, leading to the overall collapse of the tower.