The fires burned "out of control" on six of the lower floors at #7 which seriously damaged the floor framing on several floors. When a main girder on the 13th floor "lost its connection to a critical interior column that provided support for the long floor spans" on the east side of #7, that caused the 13th floor to collapse and from there on down it was like a domino effect down to the 5th floor (Stein).

In 2005 NIST published its research on 22 collapses of buildings resulting from fires. Looking specifically at the building materials used on those 22 collapses, the NIST research revealed: 7 buildings were built with concrete; 6 were built using structural steel; 5 were built with brick/masonry; 2 buildings were built using wood; and in the remaining 2 buildings it was unknown as to what materials were used (Beitel, 2005). .

Thirteen of those...
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