911-Demolition proofs

Mushrooming Tops

The Twin Towers' Tops Mushroomed As They Fell

In this photograph of the South Tower about six seconds into its destruction, the mushrooming cloud has already grown to three times the building's width. Note the dust ejection well below the mushrooming top (red arrow).

Both of the twin towers exhibited a mushrooming behavior as they collapsed, resulting in the dispersion of their steel over areas several times the size of their footprints. The mushrooming plumes of dense dust and steel began at the impact zones, and rapidly expanded. By about five seconds into each collapse the diameter of the mushrooming plume was about three times the diameter of the tower.

It is not immediately obvious to what extent the mass of the destroyed portion of the towers was dispersed throughout the clouds. However, several pieces of evidence show that most of the towers' mass landed outside of their footprints in a highly symmetric distribution.

• Photographs of the collapses show that many pieces of metal were hurled far from the towers, slightly beyond the frontiers of the dust clouds. Although some of that material may be the exterior aluminum cladding, several photos show large assemblies of the perimeter walls hundreds of feet from the towers.
• The huge hole in WTC 6 seems only explainable as the result of falling pieces of the north wall of the North Tower. The centerline of that hole is approximately 150 feet away from the tower's north wall, giving an indication of the average lateral distance its steel constituents were thrown.
• The mounds of twisted steel pieces at Ground Zero were nearly as high outside of the towers' footprints as within.

There are no photographs of the mushrooming tops of the towers in FEMA's official report -- just one poor photo of the South Tower early in its collapse -- but there is a nice graphic of the distribution of the perimeter wall column pieces (right).


































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Speed of Fall

The Towers' Tops Fell Virtually Unimpeded

The time it took the Towers to fall may be one of the most important pieces of evidence in determining their mode of destruction.

It is widely accepted that both Towers completely fell (nearly everything but the dust reached the ground) in around ten seconds. This estimate appears to be based mainly on seismic data. However, video evidence of the North Tower collapse suggests that it took close to 15 seconds for the destruction to reach the ground. Establishing a precise time of duration for each fall may not be possible, but there are measurements that can be made. Video records show that each Tower's top began its fall precipitously, and show the falling tops for a few seconds before they disappeared into the exploding dust clouds. It is also possible to track other features of the waves of destruction that traveled down each Tower. In both collapses dust clouds, exhibiting the behavior of pyroclastic flows associated with volcanoes, rapidly grew as they fell. ¹   Each cloud consumed its Tower's top in a few seconds, then continued to descend, remaining centered around the Tower's axis. Each cloud had a fairly well-defined top and bottom, whose descent can be timed using video records.

Despite the availability of detailed studies of collapse times based on the compositing of video and photographic evidence, and in-depth analysis of the seismic records, many commentors have incorrectly treated the durations of the largest seismic signals as synonymous with total collapse times. Statements that the Towers fell in eight and ten seconds have been repeated by both proponents and critics of the official explanation.

Meaning of the Seismic Records

Seismic records of the Twin Tower collapses show a large signal for each collapse lasting just under 10 seconds. The durations of the large signals are widely equated with the durations of the collapses themselves. However, the signals may correspond to only parts of the collapse events, such as the rubble reaching the ground.

Consider the seismic records of the closest seismic recording station, at Palisades, NY (PAL). They show a very similar pattern for the leveling of WTC 1 and 2. In both cases there is about five seconds of high-amplitude movement, followed by about three seconds of movement at less than half that amplitude, and then by about 15 seconds of much weaker movement. In addition there is some still weaker movement starting about 12 seconds before the onsets of the high-amplitude movement. The main difference is that for WTC 1 the initial high-amplitude phase builds in intensity to a much higher spike than any seen for WTC 2.

The fact that the largest movement is followed by smaller movement has been cited as evidence that bombs, detonated at the starts of the collapses, generated the large movement, and that the debris impacting the ground contributed to the smaller subsequent movement. However, bombs, if detonated underground, would have generated strong P waves in addition to S waves. The fact that only strong S waves were reported is consistent with the theory that the largest movement was caused by building remains hitting the ground.

Tracking the Tops

The time of onset of collapse is clear in the North Tower, which initiates its telescoping collapse in an instant. The case of the South Tower is complicated by the fact that the top leans for a few seconds before beginning its vertical descent. Although determining the onset of vertical collapse in the South Tower is more difficult, its top is visible for longer and offers a longer span through which to time the rate of fall.

The South Tower

The following analysis is based on this NBC video taken from east of the Towers.

For the South Tower we define onset of collapse as the moment downward movement of the highest point of the roof starts. Unfortunately this time is difficult to determine since the roofline is obscured by smoke when the fall begins. The fall is preceded by a leaning movement that starts at about the beginning of the video clip, and accelerates for about three seconds. At somewhere between two and three seconds, the top starts to fall. Once the top starts to lean, the highest point of the roof is the northwest edge. At about 2.5 seconds, the top starts to fall. A good marker for this is a small white squib that emerges from the level of the impact zone about three-quarters of the way back on the right face. That immediately precedes the first large ejections from the southeast face.

Using that marker it is possible to time the fall of the South Tower's top up to the moment it gets swallowed up by the dust cloud. At that point the dust cloud rises only slightly above the level of the 78th-floor sky lobby visible as a two-story band on the adjacent North Tower. A small extrapolation gives a good estimate of the time of fall of the South Tower's roof to the level of the 78th floor of five seconds. That distance is about 384 feet (12 feet per story times 32 stories).

The North Tower

The top of the North Tower began to suddenly telescope about a fourth of a second after the radio Tower started to fall. In views from the north the top is swallowed up in about two seconds. The CNN live video clip shows the mushrooming dust cloud reaching the ground at about 13 seconds. As the descending pyroclastic dust cloud drops below Building 7, the rising smoke plume shifts to the east revealing the empty space except for the short-lived spire. The first glimpse of empty space where the building stood is at about 13 seconds.

Detailed analysis of the motion of the North Tower's top is provided by physics teacher David Chandler, who measured the top and concluded that, the rapid descent of the top, though slightly slower than free-fall, means that the force it exerts on the intact portion is actually less then when the building is motionless.

The roofline of WTC1 (The North Tower) begins dropping with sudden onset and accelerates uniformly downward at about 64% of the acceleration of gravity (g) until it disappears into the dust. This means it is meeting resistance equal to about 36% of its weight. The implication of this, however, is that the force it is exerting on the lower section of the building is also only 36% of the weight of the falling section. This is much less than the force it would exert if it were at rest. The acceleration data thus prove that the falling top section of the building cannot be responsible for the destruction of the lower section of the building. ^2   3  

A Timeline for the North Tower

It would be useful if collapse events evident in videos could be associated with seismic signal features. Since some news broadcasts have real-time clocks on their banners, it may be possible to match visual events with features of the seismic signals.

Consider the North Tower, whose entire collapse was recorded by the above-mentioned CNN live feed, which has a clock on its banner. That clock does not have a second counter, but its minute counter flips to 10:29 37 seconds after collapse starts, which places the collapse start, according to the CNN clock, at 10:28:23.

Various pages on columbia.edu put the origin time of the signal at the source at 10:28:31, plus or minus one second. This is based on an estimate of 2 km/s travel speed for the S waves, which, given the PAL station's distance of 34 KM from the WTC, gives a travel time of 17 seconds.

The CNN video suggests that it takes about ten seconds for the bottom of the mushrooming dust cloud to reach the ground, and another seven or so for the top to reach the ground. The following composite timeline combines timing estimates of collapse events from the CNN video and the PAL seismic record. It assumes rubble hitting the ground caused the large ground movement, and thus that the crumbling of the Tower prior to that caused only minor ground movement. Given that, the times from these pieces of evidence match up remarkably well.

10:28:23 Top of the North Tower starts to break apart
10:28:31 Rubble starts to hit the ground (start of big signal)
10:28:36 The heaviest rubble hits the ground (peak of big signal)
10:28:39 Most heavy rubble has reached the ground (end of big signal)

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Proofs of Demolition

Demolition of the Twin Towers is Provable Through Simple Analysis

Despite the destruction of the most significant evidence of the Twin Tower collapses -- the structural steel -- it is relatively easy to prove the towers were demolished. Determining how they were demolished without the benefit of the steel may be difficult or impossible, but proving that a gravity-driven collapse is insufficient to explain the characteristics of the collapses documented by photographic and seismic evidence is not.

There are numerous pieces of evidence that strongly indicate demolition, including the fact that authorities destroyed and suppressed evidence, the more than 100 years of engineering experience with steel-frame buildings, the misleading representation of the towers' design by truss theory proponents and the implausible sequence of events proposed by that theory, and the many collapse features that seem irreconcilable with gravity-driven collapses.

Proving demolition requires more than enumerating evidence. It requires making logical inferences about events using the evidence. Three fairly strong proofs are as follows. These are presented as qualitative arguments only. Each suggests an approach for developing a rigorous quantitative proof.

• The towers fell faster than they could have if they were crushing themselves.
• The volume of dust was too great to have been the product of a gravity-driven collapse.
• The South Tower's top shattered before falling, and so its breakup was not a result of gravity-driven crushing.

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Volume of Dust

Volume of Dust Clouds Proves Demolition

Both of the Twin Towers exploded into vast clouds of dust. That the clouds expanded to five times the volume of the towers within 30 seconds of the initiation of their collapses is a conservative estimate.

If the collapses were merely gravity-driven, then any clouds of debris produced in the immediate aftermath should have occupied about the same amount of space as the intact towers before they had time to significantly mix into the surrounding air. The bulk of the clouds could only come from the expulsion of gases in the buildings as they collapsed, and the mixing of ambient air into the clouds. The contribution of mixing increases over time, and is unbounded. However, the dust clouds appear to expand more rapidly than can be accounted for by mixing. This implies that heat energy was being added to the clouds in order to cause the gases to expand, and/or water to vaporize.

Could the known energy sources have accounted for the pre-mixing expansion? This question is treated in some quantitative detail in the paper: The North Tower's Dust Cloud: Analysis of Energy Requirements for the Expansion of the Dust Cloud Following the Collapse of 1 World Trade Center. This paper estimates the dust cloud volume of the North Tower and shows that, even allowing for expansion due to mixing, the heat sink is many times greater than the tower's gravitational energy. Even without such quantitative analysis, it is clear that the gravitational energy of the towers alone could not have driven the dust clouds' expansion, given limitations on conversion of that energy to heat and the apparent absence of extensive mixing early in the clouds' development.

The expansion of the dust clouds presents problems for the gravity collapse theory that are evident without quantitative analysis. Here we consider the role of the two main factors that could have worked to expand the dust clouds.

• Heating of the air due to friction of the collapse
• Mixing of the cloud's gases and suspended solids with ambient air

Did Friction Multiply the Clouds' Volumes?

Suppose that nearly all of the gravitational energy of the towers was converted into friction and therefore heat. Would that have been sufficient to expand the dust clouds? A clue is that in a typical demolition, the volume of the dust cloud grows to only slightly larger than the intact building's volume immediately following the collapse. Even if the gravitational potential energy of the towers was great enough to drive the expansion, it is highly doubtful that much of it would be converted into heat in the dust clouds, for several reasons.

• Rubble falling through the air would not generate much heat energy until it hit the ground, and then most of the energy would be converted to ground movement and the finer breakup of the rubble rather than heat.
• Rubble crushing the building would convert much of its kinetic energy to friction in the steel frame in the process of shredding it. The steel frame would not have enough surface area to transfer much heat to the gases during the split second in which the building around any given piece of steel was crushed, so most of the heat would have ended up in the rubble pile.
• If much of the gravitational energy was converted to heat through friction, it would have necessitated longer collapse times than were observed.

At least one academic paper has attempted to explain the rapidity of the collapses by promoting a questionably applicable mathematical model alleged to predict a nearly frictionless total collapse. Since that model has each tower neatly pulling itself down at near the speed of free-fall, there would be very little heat produced to drive the dust cloud expansion.

Did Mixing Expand the Clouds?

Mixing of building air with ambient air could not account for the rapidity of the expansion of the dust clouds, nor their appearance. Mixing of gases can occur through diffusion or convection. Diffusion is not relevant, since it is the space occupied by suspended particles that defines the volume of the cloud. Convection could only expand the cloud if there was a high degree of turbulence on the cloud's boundary, and would have produced a diffuse boundary. That does not appear to have occurred in the early stages of the Twin Towers' dust clouds. The clouds maintained well-defined interfaces as they expanded to many times the buildings' volumes. Moreover, features on the surface of the clouds evolved slowly relative to the movement of large portions of the cloud. The distinct boundaries and persistent shapes mean the clouds were expanding primarily by pushing aside the ambient air, not by assimilating it.

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Breakup of WTC 2's Top

Shattering of South Tower's Top Proves Demolition

There are several pieces of evidence that show the structure of the 30 stories of the South Tower above the impact zone was shattered before it started its precipitous plunge. How could the steel frame of many stories above the impact zone have broken up even before it started to fall? The proponents of gravity-driven collapse maintain that the tops of the towers crushed the floors below the impact zones as they fell. The tops functioned as pistons, according to Bazant and Zhou, crushing the stories one by one. What one actually sees in the case of the South Tower is that their piston disintegrated even before it started to fall. A gravity-driven collapse cannot account for that disintegration, nor for how a cloud of rubble could crush the intact structure below the impact zone.

These frames from a South Tower collapse video are separated by equal time intervals. Examining the middle edge of the falling portion of the tower shows that its angle of tilt from vertical remains about the same between the second and third frames, and therefore the top has stopped rotating. But unless the top had already been shattered, it should have continued to rotate in accordance with the law of conservation of angular momentum. *****************************************************