1. If the World Trade Center (WTC) towers were designed to withstand multiple impacts by Boeing 707 aircraft, why did the impact of individual 767s cause so much damage?

As stated in Section 5.3.2 of NIST NCSTAR 1, a document from the Port Authority of New York and New Jersey (PANYNJ) indicated that the impact of a [single, not multiple] Boeing 707 aircraft was analyzed during the design stage of the WTC towers.

No one ever claimed that multiple aircraft impact had been analyzed at the design stage. Frank A. DeMartini, on-site construction manager for the World Trade Center, said in a January 2001 interview that he believed the building was sufficiently resilient to sustain multiple impacts. Months later, he was lost after the North Tower collapsed. He had remained at the scene, helping with the evacuation on the upper floors.

However, NIST investigators were unable to locate any documentation of the criteria and method used in the impact analysis and, therefore, were unable to verify the assertion that “… such collision would result in only local damage which could not cause collapse or substantial damage to the building.…”

How convenient. A paper available here concluded that about 46% of the plane's initial kinetic energy was used up in damaging the exterior columns, and the minimum velocity required to penetrate these columns would be 130 m/s (291 mph). From my own analysis, the perimeter columns (around floor ninety-eight) were no more than about 48 pounds per lineal foot or 66 lb/lineal foot allowing for the spandrel plates; the core columns ranged from around 53 (the inner core) to 257 (outer core) pounds per lineal foot. (The core column mean was about 157 lb/lineal foot.) Most of the remaining 54% kinetic energy would have been dissipated in smashing some of the 4-inch concrete slab as the plane came to a halt. Relatively small fragments of debris would have caused little damage to W14x257 or W14x193 members. With the core columns aligned such that a flange was facing the incoming debris, even in the worst-case fire of kerosene burning over a few minutes followed by aircraft combustibles and an entire floor's office fuel load burning over 102 minutes, and even if all the fireproofing had been destroyed on the exposed flange, these outer core columns could have got up to only about 400 C maximum and would have retained at least 85% of their cold capacity.

The damage from the impact of a Boeing 767 aircraft (which is about 20 percent bigger than a Boeing 707).

False. See this comparison at whatreallyhappened.com which includes links to Boeing's specifications pages. Moreover, the 767s which allegedly hit the Towers were lighter than a 707. It is generally agreed that they were only carrying about 10,000 gallons of fuel on impact. The operational empty weight of a Boeing 767-200ER is a little over 80 tonnes. If we suppose 100 kg apiece for 81 passengers and their baggage, the total is 90 tonnes plus the fuel at 3.1 kg/gal or 31 tonnes, for a total of 121,000 kg or 266,757 lb - well short of the 336,000 lb maximum take-off weight of the 707.

2. Why did NIST not consider a “controlled demolition” hypothesis with matching computer modeling and explanation as it did for the “pancake theory” hypothesis?

The Bronfmans would have had them shot or "suicided".

Based on this comprehensive investigation, NIST concluded that the WTC towers collapsed because: (1) the impact of the planes severed and damaged support columns, dislodged fireproofing insulation coating the steel floor trusses and steel columns,

The amount of "dislodged" fireproofing would have been far too minimal to have any impact on the fact that the fires could not have raised the temperature of more than a tiny fraction, if any, of the steel to greater than the critical temperature at around 550 C. Not enough of the Cafco Blaze-Shield on the trusses would have been compromised - over a sufficient number of floors, and a sufficient area on each of these floors - for the effect of the fire(s) to have been enough to tip the balance from survival to catastrophic collapse. The Boeing 767-200 series has a fuselage diameter of about 16.5 feet, i.e. less than one-tenth the width of each Tower, and less than one and a half floors in height. The floor trusses originally had 3/4 inch of FRC; by September 2001 the entire impact zone of WTC 1 (floors 92 to 99) had been upgraded to 1.5 inches with Blaze-Shield II. The tested performance of Blaze-Shield II's cohesion / adhesion strength ranges from 360 to 399 psf compared with a standard performance of 150 psf; its compressive strength has been found to be from 1,700 to 2,380 psf.

"Preliminary calculations suggest that the resulting overpressures [from the fireballs] were less than 1 lb per square inch (PSI)...It is likely that the force of the impact and the speed with which debris travelled through the structures compromised the sprayed-on fire protection of some of the steel members in the immediate areas of the impact."

Civil Engineering Magazine, May 2002

"The force of the impact and the resulting debris field and fireballs probably compromised spray-applied fire protection of some of the steel members in the immediate area of impact. The exact extent of this damage will probably never be known..."

FEMA 403, Chapter Two, 2-24

An overpressure of "less than 1 psi", i.e. less than 144 psf.

It is fair to say that some of the FRC on some trusses in the immediate impact area was compromised by debris. The deflagration overpressure was far too low to damage fireproofing. The main damage area in WTC 1 would have been a rectangular section of some 17 feet in width and 60 feet in length from the north face to the core, and much of this tiny proportion of two or three floors would have been already destroyed by the impact. ("AA 11" had a descent angle of about 10 degrees, so 68 feet horizontally - taking it into the core - would correspond to a 12 feet height drop which makes for an extra floor albeit at reduced length of damage zone.) The west, south and east sides would have undergone relatively little damage in the inter ceiling-floor zone; floors above and below likewise. The truss-initiated collapse theory requires total collapse and removal of at least five floors, which would not have happened in 102 minutes of release of some 10^12 joules per floor with almost all of the truss FRC remaining even on the worst floors. Each WTC floor had about 56 tons of fireproofing, so the FRC over three floors at 168 tons was more massive than the plane and its fuel. The Blaze-Shield would not have been "blown" off the trusses.

Since the impacting debris (from "Flight 11") was approaching at a descent angle of about ten degrees, most of the trusses were shielded from this by four inches of solid concrete. Where the debris did not smash its way through the concrete, most of the FRC on the trusses would have remained intact. The height of the trusses was 29 inches, so from 29 inches / tan [10 degrees] we have 164 inches, say 14 feet, as the length of the strip where the truss bottom chord might have had its FRC compromised in places, beyond the extent of the smashed concrete. The width of the strip is 17 feet, from the diameter of the plane fuselage, so 14 x 17 feet is 238 square feet. At 207 feet by 207 feet, each floor was 42,849 square feet, so the area of possibly partially compromised bottom chord FRC is some 0.6% of the total floor area. Wing debris (from part of a single wing for a given floor due to the aircraft roll of about 25 degrees), and debris bouncing off a floor and smashing through ceiling tiles (which were 2 psf), could have added a little, but not enough to prefer the fire collapse theory over the controlled demolition theory.

and widely dispersed jet fuel over multiple floors; and (2) the subsequent unusually large jet-fuel ignited multi-floor fires (which reached temperatures as high as 1,000 degrees Celsius) significantly weakened the floors and columns with dislodged fireproofing

False. See above.

to the point where floors sagged and pulled inward on the perimeter columns. This led to the inward bowing of the perimeter columns and failure of the south face of WTC 1

The south face of the North Tower was, at worst, only hit by a few fragments of plane debris at relatively low velocity. If any South Tower debris had hit it, it would have impacted at too low a velocity to significantly damage columns. Sufficient fireproofing would have remained on the trusses to inhibit any mechanism for "sagging" of floors, and controlled demolition remains the only credible mechanism for collapse of at least five floors and / or initiation of global collapse.

NIST’s findings also do not support the “controlled demolition” theory since there is conclusive evidence that: the collapse was initiated in the impact and fire floors of the WTC towers and nowhere else,

The perpetrators had pre-selected the target floors. Explosives were rigged accordingly, and operators used Dov Zakheim's S.P.C.-built remote transceivers to fly the planes into the target floors. And as the thermite began to take out many of the core columns, perimeter column failure would have initiated at the weakest point.

and the time it took for the collapse to initiate (56 minutes for WTC 2 and 102 minutes for WTC 1) was dictated by

...when the operators in WTC 7 noticed that the office fires were going out.

6. How could the WTC towers collapse in only 11 seconds (WTC 1) and 9 seconds (WTC 2)—speeds that approximate that of a ball dropped from similar height in a vacuum (with no air resistance)?

NIST estimated the elapsed times for the first exterior panels to strike the ground after the collapse initiated in each of the towers to be approximately 11 seconds for WTC 1 and approximately 9 seconds for WTC 2. These elapsed times were based on: (1) precise timing of the initiation of collapse from video evidence, and (2) ground motion (seismic) signals recorded at Palisades, N.Y., that also were precisely time-calibrated for wave transmission times from lower Manhattan (see NCSTAR 1-5A).

As documented in Section 6.14.4 of NIST NCSTAR 1, these collapse times show that:

“… the structure below the level of collapse initiation offered minimal resistance to the falling building mass at and above the impact zone.

Probably correct, although dust clouds render video footage inconclusive.

The potential energy released by the downward movement of the large building mass far exceeded the capacity of the intact structure below to absorb that energy through energy of deformation.

My analysis of the WTC specifications concluded that the gravity load of floors 98 - 110 of WTC 1 was about 34,573 tons. The drag equation D=Cd*0.5*V^2*A*r derives from the laws of momentum. Where M1*V1 + M2*V2 = M1*Vf + M2*Vf in the case of an inelastic collision, the worst-case situation of all displaced particles from a fluid being forced to move in the direction of the moving solid rather than displaced sideways to flow around it would correspond to Cd = 2, hence D=V^2*A*r. A light office floor such as floor 97 had a total mass of 1,771 tons (316 tons superimposed dead load, 337 tons superimposed live load, 785 tons concrete dead load, and 333 tons steel dead load). Its volume was 207 x 207 x 12 = 514,188 cubic feet; hence its density was 6.889 pcf or 110.3 kg/m^3. Let's say 111 kg/m^3 including air.

So if we treat the intact solid section below as a "fluid", not allowing for the energy sink of pulverising the concrete and tearing apart the steel, and not allowing for the heavier mechanical floors and the heavier steel columns on the lower floors, and set Cd to 2 which cancels out the 0.5 in the original equation, we have 34,573 tons ~ 31,365,000 kg as the moving mass in a fluid of density 111 kg/m^3. The downforce from gravity is 9.806*31,365,000 = 307,565,190 N. From the uplift D=V^2*A*r we have V=SQR(D/(A*r)) to obtain the velocity where the uplift equals the downforce. From SQR(307,565,190/(4,000*111)) we find the terminal velocity is around V = 26.32 m/s or 86.35 fps or 58.87 mph. Even if the moving mass had progressed at a constant 86.35 fps from a height of 1,212 feet, it would take some 14 seconds for the former floor 98 to hit the ground. The thirteen-floor section was 156 feet, which adds another 1.8 seconds. Running simulations which start at zero velocity and compute the forces every 100 uS to 10 mS of simulated time, the times from a standing start are about 15.9 seconds plus 1.8 seconds for a total of 17.7 seconds.

Although the 9/11 commission report actually admitted that the South tower collapsed in 10 seconds, and NIST talks about the "times for the first exterior panels to strike the ground" at 11 and 9 seconds for WTC1 and WTC2 respectively, the official conspiracy theorist could claim that "the first exterior panels" fell outwards and avoided the more slowly moving interior. Times of some thirteen to sixteen seconds for WTC 1 are quite possible from the evidence, since there is a grey area of about eight seconds when the view was obscured by dust clouds. There is enough uncertainty here that the collapse time is not a particularly good argument for or against controlled demolition, although the collapse times and the nature of the collapses such as pulverization of concrete and lack of stutter tend to favor CD. The best argument for controlled demolition is the fact that all three skyscrapers did in fact collapse after remaining stable for many minutes following physical damage, when the presence of Cafco Blaze-shield or Monokote fire resistive coating on almost all of the steel (or all in the case of WTC 7) would have prevented all but a tiny fraction, at most, from reaching dangerously high temperatures.

Since the stories below the level of collapse initiation provided little resistance to the tremendous energy released by the falling building mass,

If the "Bin Laden office fires-induced collapse" hypothesis were true, the resistance would not have been "little".

the building section above came down essentially in free fall, as seen in videos.

NIST said the building section "came down essentially in free fall", Larry Silverstein said that they decided to "pull" Building 7, and Rumsfeld spoke of "the missile" that damaged the Pentagon. However, convictions should ultimately be based upon physical evidence of crimes, rather than the criminals' own words.

Both the NIST calculations and interviews with survivors and fire-fighters indicated that the aircraft impacts severed the water pipes that carried the water to the sprinkler systems. The sprinklers were not operating on the principal fire floors.

Very convenient for the "Bin Laden" theorists. This hypothesis doesn't work for Building 7, which was not hit by an aircraft.

9. If thick black smoke is characteristic of an oxygen-starved, lower temperature, less intense fire, why was thick black smoke exiting the WTC towers when the fires inside were supposed to be extremely hot?

Nearly all indoor large fires, including those of the principal combustibles in the WTC towers, produce large quantities of optically thick, dark smoke. This is because, at the locations where the actual burning is taking place, the oxygen is severely depleted and the combustibles are not completely oxidized to colorless carbon dioxide and water.

The visible part of fire smoke consists of small soot particles whose formation is favored by the incomplete combustion associated with oxygen-depleted burning. Once formed, the soot from the tower fires was rapidly pushed away from the fires into less hot regions of the building or directly to broken windows and breaks in the building exterior. At these lower temperatures, the soot could no longer burn away. Thus, people saw the thick dark smoke characteristic of burning under oxygen-depleted conditions.

The consequence of this is that the fires are cooler. Under optimum (stoichiometry of phi = 1) conditions, some 17 MJ of heat would be released per kilogram of wood equivalent fuel burned. In the oxygen-depleted compartment fire, the heat liberated per kg of wood is reduced to about 11.5 MJ, or about 68% combustion efficiency.

11. Why do some photographs show a yellow stream of molten metal pouring down the side of WTC2 that NIST claims was aluminum from the crashed plane although aluminum burns with a white glow?

NIST reported (NCSTAR 1-5A) that just before 9:52 a.m., a bright spot appeared at the top of a window on the 80th floor of WTC 2, four windows removed from the east edge on the north face, followed by the flow of a glowing liquid. This flow lasted approximately four seconds before subsiding. Many such liquid flows were observed from near this location in the seven minutes leading up to the collapse of this tower. There is no evidence of similar molten liquid pouring out from another location in WTC 2 or from anywhere within WTC 1.

Photographs, and NIST simulations of the aircraft impact, show large piles of debris in the 80th and 81st floors of WTC 2 near the site where the glowing liquid eventually appeared. Much of this debris came from the aircraft itself and from the office furnishings that the aircraft pushed forward as it tunneled to this far end of the building. Large fires developed on these piles shortly after the aircraft impact and continued to burn in the area until the tower collapsed.

NIST concluded that the source of the molten material was aluminum alloys from the aircraft, since these are known to melt between 475 degrees Celsius and 640 degrees Celsius (depending on the particular alloy), well below the expected temperatures (about 1,000 degrees Celsius) in the vicinity of the fires. Aluminum is not expected to ignite at normal fire temperatures and there is no visual indication that the material flowing from the tower was burning.

Pure liquid aluminum would be expected to appear silvery. However, the molten metal was very likely mixed with large amounts of hot, partially burned, solid organic materials (e.g., furniture, carpets, partitions and computers) which can display an orange glow, much like logs burning in a fireplace. The apparent color also would have been affected by slag formation on the surface.

This is certainly an interesting phenomenon. At least NIST are honest and realistic enough to admit that the aluminum did not burn and thereby generate heat, since that would have required it to have been in the form of flakes or a fine powder.

Suppose we take an (on the high side) estimate of 1000 C for flame and hot gas upper layer temperatures in very close proximity to a plate of aluminum alloy just as it is supposed to have melted. If the aluminum was at the low end of the aircraft fuselage skin thickness range at some 0.03 inches or 0.000762 m and its area was 0.485 m^2, this would place the volume of the piece around 0.00037 m^3 and hence its mass would be 0.00037 * 2700 kg/m^3 ~ one kilogram. The heat required to melt this is given by the temperature increase of (660 - 25) which is 635 degrees K times the heat capacity of 900 J/kg.K (it's actually more than this over the range up to 660 C) which comes to 571,500 J, plus 397 kJ for the latent heat of fusion, to give a total requirement of 968.5 kJ. After allowing for elements such as zinc in the alloy, the melting point, specific heat and enthalpy of fusion would be slightly lower.

So we have this piece of aircraft debris which just happens to have settled such that its 0.485 m^2 area side is squarely facing the radiant heat from the flames of burning office stationery, carpets, workstations, etc, and in a vertical position against the wall at the top of a window. Suppose it has already reached 660 C (or slightly less for the alloy), after absorbing the initial 571.5 kJ. The rate of radiant heat transfer is related to the difference in the fourth powers of the absolute temperatures of emitter and absorber:

P = e * lowercasesigma * A * (Te^4 - Ta^4)

For the moment, we suppose emissivity e = 1. Taking the Stefan-Boltzmann constant (lowercasesigma) as 5.6703 * 10^-8 W/m^2.K^4, we have:

P = 5.6703 * 10^-8 * 0.485 * (1273^4 - 933^4) = 51.382 kW.

(If the emitter temperature is lowered from 1000 to 900 C, P drops to 31.225 kW.)

At 397 kJ required to melt the 1 kg after it has reached the melting point, the time required is 397 / 51.382 = 7.726 seconds, or slightly less for the alloy, or almost 12.7 seconds assuming 900 C for the emitter temperature.

A major problem with the "melting aluminum" theory is that aluminum is a poor absorber of radiant heat. Although it is not unreasonable to take 1 as the emissivity of flames, aluminum has an emissivity of only about 0.1. This is why it is used as a reflector in infrared heaters. Also, for a thin plate of aluminum, some radiation would be transmitted through it. Moreover, the location by the window would result in a further 40% or so reduction. At 1000 C (flame) and 660 C (aluminum) the potential aluminum absorption is proportional to 1273^4 - 933^4, i.e. 1.868*10^12, and it would be likely to transmit an amount to the exterior proportional to 933^4 - 298^4, i.e. 7.499*10^11. If in close contact with the wall, it would conduct heat to it.

Most of the radiant heat striking the aluminum would be reflected back, and would probably end up being vented out to drive the smoke plume.

A ten-fold adjustment raises the minimum time for melting of the 660 C aluminum from the above 7.726 seconds to 77.26 seconds. Yet there was enough melting liquid to be clearly visible, and to sustain a four-second flow before subsiding. Even if the whole 1 kg had somehow resisted melting for 77 seconds whilst receiving heat at 660 C, and then the entire piece suddenly melted within a mere 4 seconds, aluminum only expands by about 12% when molten to a density of 2400 kg/m^3. So the 1 kg would have a volume of 417 ml which is barely more than the contents of a can of Coke. The video evidence shows that the flow was much more than 100 ml per second, and at times more like a "waterfall". And...

Many such liquid flows were observed from near this location in the seven minutes leading up to the collapse of this tower.

...which would be many, many kilograms of aluminum, and would require a greater energy source than a few burning papers and carpets in an office compartment fire.

There was aluminum cladding on the exterior columns, but this was on the three exterior sides and on the wrong side of fire-resistant plaster. The flows of molten liquid support the theory that thermite or thermate played a part in weakening columns over the space of several minutes leading up to each collapse. It is hardly surprising that guards were immediately placed at the crime scene, Ground Zero, to prevent independent investigators from getting hold of samples of steel, and a couple of weeks later Mayor Giuliani even banned photography at the site.

12. Did the NIST investigation look for evidence of the WTC towers being brought down by controlled demolition? Was the steel tested for explosives or thermite residues? The combination of thermite and sulfur (called thermate) "slices through steel like a hot knife through butter."

NIST did not test for the residue of these compounds in the steel.

The responses to questions number 2, 4, 5 and 11 demonstrate why NIST concluded that there were no explosives or controlled demolition involved in the collapses of the WTC towers.

See above reply re the Bronfmans, which is the true answer here.

Furthermore, a very large quantity of thermite (a mixture of powdered or granular aluminum metal and powdered iron oxide that burns at extremely high temperatures when ignited) or another incendiary compound would have had to be placed on at least the number of columns damaged by the aircraft impact and weakened by the subsequent fires to bring down a tower. Thermite burns slowly relative to explosive materials and can require several minutes in contact with a massive steel section to heat it to a temperature that would result in substantial weakening. Separate from the WTC towers investigation, NIST researchers estimated that at least 0.13 pounds of thermite would be required to heat each pound of a steel section to approximately 700 degrees Celsius (the temperature at which steel weakens substantially). Therefore, while a thermite reaction can cut through large steel columns, many thousands of pounds of thermite would need to have been placed inconspicuously ahead of time, remotely ignited, and somehow held in direct contact with the surface of hundreds of massive structural components to weaken the building. This makes it an unlikely substance for achieving a controlled demolition.

Thermite played a role in weakening the buildings in the minutes preceding collapse; other charges were used at collapse time. Some charges in the basement were either set off by the aircraft impact, or were detonated seconds sooner than planned. If "exploding jet fuel" had caused the reported basement explosions, the aircraft impact would have needed to have preceded the explosions by almost nine seconds, whereas eyewitnesses reported explosions actually before the impact of the plane. The official theory requires that "devout Muslim suicide pilots" (who were also gamblers, drinkers and womanizers), masterminded by a man in a cave, managed to elude airport CCTVs and the entire US Air Force as they flew around US airspace, somehow persuaded the pilots to hand over control of the planes whilst armed with nothing more than box cutters, knew how to turn off the transponders, developed the flying skills of crack fighter pilots after one of them was even refused permission to fly a Cessna, and successfully provided PNAC and Israel with the "new Pearl Harbor" that they desired as a pretext with which to invade oil-rich or opium-rich Muslim nations and hand over the armed forces of the US, UK, Australia, Italy, Spain, etc as Israel's proxy army to fight its enemies for free; whilst at the same time providing the incident to "bury the bad news" of the previous day's announcement of a $2.3 trillion hole in the Pentagon's finances, and handing the new WTC leaseholder and insurance beneficiary billions or dollars into the bargain. This renders it an unlikely conspiracy theory even before we allow for the physical impossibility of three fireproofed steel-framed high-rises collapsing in a single day.

13. Why did the NIST investigation not consider reports of molten steel in the wreckage from the WTC towers?

NIST investigators and experts from the American Society of Civil Engineers (ASCE) and the Structural Engineers Association of New York (SEONY)—who inspected the WTC steel at the WTC site and the salvage yards—found no evidence that would support the melting of steel in a jet-fuel ignited fire in the towers prior to collapse.

Of course they found no such evidence, since that would have been impossible.

The condition of the steel in the wreckage of the WTC towers (i.e., whether it was in a molten state or not) was irrelevant to the investigation of the collapse


since it does not provide any conclusive information on the condition of the steel when the WTC towers were standing.

Nonetheless, it is evidence of foul play. And it is a pretty good indication that some of the steel was molten at the time of collapse.

NIST considered the damage to the steel structure and its fireproofing caused by the aircraft impact and the subsequent fires when the buildings were still standing since that damage was responsible for initiating the collapse of the WTC towers.

Under certain circumstances it is conceivable for some of the steel in the wreckage to have melted after the buildings collapsed.

...circumstances such as thermite reactions continuing shortly after collapse, and molten steel trapped within insulating piles of rubble.

Any molten steel in the wreckage was more likely due to the high temperature resulting from long exposure to combustion

This is not possible with hydrocarbon combustion, especially in an oxygen-starved environment.

within the pile than to short exposure to fires or explosions while the buildings were standing.

Consider the silly notion that the potential energy from the "massive collapse" might have been responsible for melting the steel. Let's suppose hundreds of thousands of tons of steel was travelling at 100 mph, and all of its kinetic energy was converted into heat in an inelastic collision and was used to heat the entire mass of steel. The kinetic energy is given by:

KE = 0.5*m*v^2

and the temperature rise of the steel is given by:

T2 - T1 = 0.5*m*v^2 / (c*m) = 0.5*v^2 / c

where c is the specific heat of the material.

The mass is irrelevant to the temperature increase, which is determined merely by the velocity and the specific heat. (The units are chosen so that units of mass and velocity correspond to the equivalent units in kinetic energy, and units of mass in the specific heat). So 100 mph = 44.7 m/s, and we'll take c for steel as 450 J/kg.K, which places the increase in temperature at:

0.5 * 44.7^2 / 450 = 2.22 degrees K.

The fire collapse theorist might suggest that there were relative "hot spots". But they would have to be far hotter than the mean. Even a hot spot that was 500 times the mean increase would only be at 1110 degrees above ambient temperature. Unless this happened to coincide with steel that had already been appreciably heated, it would not melt. And the total mass would not have been so unevenly distributed across the building's footprint and so clumped together at a particular point in collapse time that some points would experience a bump 500 times bigger than the mean, and other points would escape with 500 times below the mean. 400,000 tonnes distributed over an area of 4,000 square metres would average 100 tonnes per square metre. There would not be a square metre where 50,000 tonnes was piled up at 500 times the mean debris height, and another square metre in the footprint that only got hit by 200 kg of material.

14. Why is the NIST investigation of the collapse of WTC 7 (the 47-story office building that collapsed on Sept. 11, 2001, hours after the towers) taking so long to complete? Is a controlled demolition hypothesis being considered to explain the collapse?

When NIST initiated the WTC investigation, it made a decision not to hire new staff to support the investigation. After the June 2004 progress report on the WTC investigation was issued, the NIST investigation team stopped working on WTC 7 and was assigned full-time through the fall of 2005 to complete the investigation of the WTC towers. With the release and dissemination of the report on the WTC towers in October 2005, the investigation of the WTC 7 collapse resumed. Considerable progress has been made since that time, including the review of nearly 80 boxes of new documents related to WTC 7, the development of detailed technical approaches for modeling and analyzing various collapse hypotheses, and the selection of a contractor to assist NIST staff in carrying out the analyses. It is anticipated that a draft report will be released by early 2007.

The current NIST working collapse hypothesis for WTC 7 is described in the June 2004 Progress Report on the Federal Building and Fire Safety Investigation of the World Trade Center Disaster (Volume 1, page 17, as well as Appendix L), as follows:

An initial local failure occurred at the lower floors (below floor 13) of the building due to fire and/or debris-induced structural damage of a critical column (the initiating event) which supported a large-span floor bay with an area of about 2,000 square feet;

Vertical progression of the initial local failure occurred up to the east penthouse, and as the large floor bays became unable to redistribute the loads, it brought down the interior structure below the east penthouse; and

Triggered by damage due to the vertical failure, horizontal progression of the failure across the lower floors (in the region of floors 5 and 7 that were much thicker and more heavily reinforced than the rest of the floors) resulted in a disproportionate collapse of the entire structure.

In other words, NIST are still trying to concoct a work of fiction.

This hypothesis may be supported or modified, or new hypotheses may be developed, through the course of the continuing investigation. NIST also is considering whether hypothetical blast events could have played a role in initiating the collapse. While NIST has found no evidence of a blast or controlled demolition event, NIST would like to determine the magnitude of hypothetical blast scenarios that could have led to the structural failure of one or more critical elements.

The fire / debris-induced hypothesis requires replacing. The results are eagerly awaited.

Revised 11 September 2006

Our theory on how the demolition was carried out.

Gordon Ross's site has another theory.