9/11 FEITEN: ooggetuigen en analyses

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After WTC 2 collapsed:
* Some south face glass broken at lower floors
* dust covered lobby areas at floors 1 and 3
* power on in building, phones working
* no fires observed

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After WTC 1 collapsed:
* heavy debris on VEsey street and WTC 7 promenade
* no heavy debris observed in lobby area, white dust coating
* SW corner damage - floors 8 to 18
* south face damage between two exterior colums -roof level down 5 to 10 floors - extent not known
* south face damage:
* middle 1/4-1/3 width south face - 10th floor to ground
* large debris hole near centre around 14th floor
* 1/4 width south face, above 5th floor, atrium glass intact
* 8th/9th floor from inside, visible south wall gone with more damage to west, 2 elevator cars dislodged into elevator lobby

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Observer fire locations:
General
* no diesel smells reported from the exterior, stairwells or lobby
* no signs of fire or smoke below floor 6 from stairwell and lobby areas
* fire reported at west wall of floor 7 around 12:15 pm
* in east stairwell, smoke was observed near floors 19-20, signs of a fire observed on floor 23
looking from SW corner to south face
* Fire in SW corner near floor 10 or 11
* fire on floors 6, 7, 8, 21, 30
* multiple fires observerd on floors 20s and 30s
* heavy black smoke coming out of south face gash, no fire observed
Looking form SE corner to south face
* fire on floor 121, area above covered with smoke
* fire on floors 11-121, moved to east face and progressed to north

1fires reported on floor 14, but photographs show east face fires on floor 12

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Failure sequence timeline
(sec)
0.0 Movement of east penthouse roofline
0.9 East penthouse kinks between columns 44 and 45; 2 windows at floor 40 fail between colums 44-45
1.2 4 windows fail at floor 40; east penthouse submerged from view (now inside buidling)
1.7 3 windows break at floors 41 to 44
4.0 windows break along column 46 at floors 37 and 40
7.0 north side of west penthouse moves; movement of entire north face of WTC7 (visible above floor 21)
7.2 west end of roof starts to move
7.7 east end of roof starts to move; facade kink formed along columd 46-47
7.9 west penthouse submerged
8.2 global collapse occurs as windows fail between floors 33-39 around column 55

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A working collapse hypothesis has been developed with four phases:
* an initiating event
* vertical progression on the east side
* horizontal progression from east to west
* global collapse

initiating event
first exterior sign of failure was at the east penthouse rooflinen, alignes with interior columns 79, 80 and 81. Postulated events include the failure of these colums.

vertical progressions
Colums 79, 80 and 81 supported large tributary areas for floors spans of app. 50 ft. Failure of column 79, 80 and 81 would likely result in failure at the floor-column connections and would progress vertically up to the east penthous.

horizontal progression
* a vertical failure would pile debris on the east side of the building, damaging or severing transfer girders and trusses between floors 5 and 7
* this secondary damage has been postulated to cause a horizontal progressoion of failure in the core columns at or near floors 5 and 7.

global collapse
the global collapse ocured with few external signs and is postulated to have occured with the failure of core colums

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status
* a working hypothesis had been developed
* the hypothesis is consisten with visual observations