Buildings 5 and 6 did not collapse, yet those buildings were engulged with fire.
Huge Amounts Of Smoke Came From WTC 5 & 6 NOT WTC 7
These photos show that Buildings 5 and 6 were 12 strories high, and could almost entirely be reached with water hoses. There were substantial breaches to the outer shells of 5 and 6, so no heat was building up in building 5 and 6.
All the people had been evacuated from Building 7, and the fire hoses could not reach very far up the 47 story building. The upper exterior shell of Building 7 was largely intact. The intact upper exterior of building 7 held in the heat from the fires on middle floors.
The NYFD had no effective plan for fighting the multi-story fire in Building 7, there was already significant structural damage to a lower corner of Building 7, and a command decision was made that enough firefighters had already died on 9-11, so no efforts were made to combat the fire in Building 7.
Heat rises, and as the fire burned from at least 10:28 AM to 5:20 PM, the heat built up inside, and the heat rose to the floors above the fire in the building.
The NYFD could have done more to cool off Building 7, so maybe the NYFD wants to say they were surpriesd the Building 7 collapsed from heat build up inside the building.
It was not well understodd on 9-11-01 that Steel weakens when heated. It was not well understood, that as a fire burns on the lower floors of an office building, that the floors immediately above the fire will become overheated, lose their structural strength, and bring more weight to bear on the floor immediately below the fire, so that the weight of floors 20 through 27 will overload floor 20, and start a collapse. Floors 19, 18, 17 each will become succesively overladed and collapse.
I have seen several fires in high rise apartments, and the apartments are desiged to contain gthe fire within that one apartment. So the fire is encapsulated, and does not threated the apartments above or beside the aparment on fire.
For Office Buildings, there is no such copmartmentalization. One floor on fire, burns up to the next floor. Heat keeps building up, and weakens the steel and overloads the floor at the base of the fire.
Fire fighting efforts on Building 7 stopped at Noon, on 9-11.
Context of '(5:20 p.m.) September 11, 2001: WTC Building 7 Collapses; Cause Remains Unclear'
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