WTC destruction comparison matrix

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9/11: WTC destruction comparison matrix


This page is for comparison of the following, with regard to the destruction of steel-framed high-rise buildings:

The Matrix


The left side of the table ("CAUSE") shows attributes found in common causes of building collapse. The right side of the table shows actual attributes observed in the collapses of WTC1, WTC2, and WTC7.

CAUSE → demolition earthquake explosion fire BUILDING → WTC1 WTC2 WTC7
Y N  ? N Y  ? Y
Clean cuts Y N  ? N Y? Y?  ?
Collapse zone Y N  ?  ? Y Y Y
-- at bottom Y  ?  ?  ? N N Y
N Y  ? Y N N N
Deformations N Y  ? Y N  ? N
Ejection N N Y N Y Y N
Flashes Y N  ? N Y Y  ?
Free-fall Y N  ? N Y Y Y
Molten steel Y N  ? N Y Y Y
Pulverization Y N Y N Y Y  ?
Recognizable N Y  ? Y N N N
Squibs Y N  ? N Y Y Y?
Symmetry Y N  ? N Y Y Y
Toppling N Y  ?  ? N y/n N

The most rigorous way to pursue this analysis would be to have a complete list of all known steel-frame building collapses which have been described in any detail (or for which there are images or videos), and come up with a correlation between each cause-of-collapse and each collapse attribute. It would then be possible to calculate, with a reasonably small margin of error, the likelihood of each possible cause-of-collapse being responsible for each of the three collapsed WTC buildings.

I don't know where to find such data at this time, but one can certainly begin compiling a list of steel-frame building collapses along with any details known.


  • Center first: the middle of the building begins collapsing slightly before the outside edges
  • Clean cuts: where shaped charges were used to sever steel beams, the cuts are clean and typically at a sharp angle (to control the direction of collapse)
  • Collapse zone: the area of the building where most of the collapsing and disintegration takes place. In controlled demolitions, the collapse zone is at the base of the building; above this point, the building is largely intact as it falls. In other types of collapse, there may be multiple points of collapse, and disintegration after the initial failure does not progress smoothly or continuously; there typically is no "zone" where collapsing occurs as a continuous process.
  • Comparable size: the rubble of the collapse is of a size/volume comparable to the original structure
  • Deformations: notable deformations in the building's structure are visible before the onset of collapse
  • Ejection: solid materials are ejected forcefully from the building during collapse, typically in a horizontal direction, landing some distance away from the main body of the post-collapse structure
  • Flashes: faint flashes of light are seen shortly before and during collapse
  • Free-fall: building collapses quickly; technically not "free-fall" speed, but within an order of magnitude
  • Pulverization: large volumes of dust are produced
  • Recognizable: after collapse, the building is still recognizably the same structure, albeit severely distorted by the collapse. Basic structural frame is still holding together.
  • Squibs: small puffs of dust or smoke seen shortly before onset of collapse or during collapse
    • actually a slight misnomer; the term "squib" technically refers to the devices which cause these puffs – but within the context of this discussion, we'll use it to refer to the puffs themselves
  • Symmetry: the building collapses nearly symmetrically, rather than from one side first
  • Toppling: the building collapses on its side, with significant horizontal displacement and deviation from the vertical

Also need one or more attributes having to do with the characteristics of fire: evidence of extreme heat, color of smoke, degree to which building is engulfed in flame. Note that fire has never caused collapse of a high-rise.


  • demolition (short for controlled demolotion): rapid onset, symmetrical, collapses from bottom, collapses inward into its own footprint, collapses quickly, squibs above point of explosion, clouds of dust and smoke, center first, collapsed building unrecognizable / no integrity, small chunks, molten iron often found (from thermite)
  • earthquake: asymmetrical, toppling, recognizable integrity
  • explosion: thick, dense, billowing, enormous clouds of dust and smoke, flashes of light, explosive sounds
  • fire: (has never caused a high-rise to collapse, so only examples are from smaller buildings)


Some notes on observed characteristics of the collapses of the WTC buildings

  • Center first:
    • WTC1: the antenna mast started coming down shortly before the outside of the building.
    • WTC7: the "penthouse" at the top center of the main roof started coming down shortly before the rest of the roof; the roofline visibly sags in the middle at the beginning of collapse.
  • Clean cuts: there are at least two photographs showing girders in the wreckage of WTC1 or 2 cleanly cut at a steep angle, described by architect Richard Gage as exactly the sort of thing one would see had thermite been used. (Need to collect some pictures of known cases of thermite usage.) The angle of the cuts also contradict any suggestion that the cuts were the result of the demolition process, because demolition workers generally cut straight through in order to minimize the cross-section they have to cut through (less work, less time). It should be noted, however, that to whatever extent there is any doubt that demolition workers might have made these cuts, this is a further indictment of authorities who allowed the steel to be cut up and hauled off before being examined forensically.
  • Deformation: The closest thing to a deformation in any of the WTC buildings prior to collapse was the tilting of the top floors of WTC2 about 1 second before collapse began. The structural damage from the airplane impact might conceivably have been the cause of this tilting, if it turns out that the tilting was in the direction of the aircraft's entry point (to be investigated), as this would (intuitively) be the point of greatest damage.
  • Molten steel was observed pouring from WTC2 less than a minute before the collapse; pools of molten steel were found in the collective rubble of WTC1&2, as well as in the rubble of WTC7. One of the investigations claimed that this might have been molten aluminum from the aircraft, which would melt at normal fire temperatures, but experiments with molten aluminum have failed to produce results with a similar appearance to what appears on video recordings (and certainly does not explain the pools found in the rubble).
  • Toppling: The top floors of WTC2 began toppling shortly before demolition, but this does not appear to be related to the main body of the demolition: toppling of part of a building would not appear to have ever caused the remainder of the building to collapse in a straight-down direction, therefore something else must have caused the remainder of the collapse.


Two building collapses in the far East are sometimes cited as evidence that structural collapses can appear like controlled demolition.

South Korea: Sampoong Department Store

Singapore: Hotel New World

Hotel New World, built 1971

  • described as "unremarkable"
  • 36 reinforced concrete columns
  • 6 concrete floors
  • basement garage
  • A/C units and water tanks on roof
  • Only significant prior incident: gas leak poisoned 35 people in 1975; all recovered


  • 19:00 Madam Lily Tao (sp) notices crack in structural column. She informs owner; workmen begin repairing the damage.
  • 21:15 A wall mirror breaks in the staff changing room


  • 10:10 A bank customer (bank is on ground floor), out of breath, reports debris falling in the garage. Two staff investigate; workmen tell them everything is ok.
    • In the hotel (2 floors up), staff see cracks spreading in the wall, but apparently do not report it.
  • 11:22 Cristina sees falling debris, feels the floor shaking
  • 11:26 Building begins to shake, pillars crack, walls give way