In his introduction to the interview, Attivissimo remarks, "Clifton's professional opinion dispels all of the doubts raised by conspiracy theorists regarding the three collapses and makes it very clear that for the experts there is no mystery at all."

Charles Clifton's original focus in his engineering career was on the impact of earthquakes on steel structures. He claims that he later went on to study the impact of fire on buildings. The only thing he appears to have written on 9/11, however, was a paper published in December 2001, "Elaboration on Aspects of the Postulated Collapse of the World Trade Centre Twin Towers." Unfortunately, the paper seems to have disappeared from the internet. Clicking on the link causes this message to appear: "The requested resource (/PDF%20Files/Elaboration%20on%20WTC%20Paper.PDF) is not available."

Inasmuch as the paper appeared in the journal HERA, Innovations in Metals before the dust had completely settled on Ground Zero, it would be interesting to see how Mr. Clifton acquired enough technical information to elaborate on the scientific aspects of the WTC collapse so quickly and to have his conclusions published in a journal printed for release in December 2001. The timing would mean that he completed his investigation within just weeks of the catastrophic events. It has taken other experts years of painstaking investigation to develop their conclusions, so it would be intriguing to find out from him how he arrived at his own so quickly. Perhaps Mr. Clifton would agree to be interviewed by AE911Truth so that he can answer questions related to this as well as to his other statements in this interview.

The following are excerpts from the interview with our rebuttal in italics:

Charles Clifton: What happened with the World Trade Center 1 is ... the plane destroyed a large chunk of the core immediately at impact and severely weakened the rest of it.

This is incorrect. Since the rest of his theory is built on this fallacy, the theory as a whole is invalid. Although many of the core columns were damaged, the rest were NOT weakened. Five core columns only had light damage and 27 had no damage at all.

Per NIST (from NCSTAR 1-2, p. 211 [PDF p325], http://www.nist.gov/customcf/get_pdf.cfm?pub_id=101012): "Cumulative structural damage to floors and columns of WTC 1 (more severe case): 6 core columns severed, 3 core columns severely damaged, 6 core columns moderately damaged, 5 core columns lightly damaged, 27 of 47 core columns undamaged."

Undicisettembre: What do you think about conspiracy theories according to which the upper block could not have enough momentum to make the whole building collapse?

The question uses misleading rhetoric ('conspiracy theories') to discourage rational consideration of theories other than the official one. A conspiracy is an illegal or subversive act planned by two or more people. That has nothing to do with the laws of physics, which is what the question is about. "Bin Laden's 19 hijackers brought down the towers with jetliners" is a conspiracy theory, but "The World Trade Center Towers and building 7 collapsed in the manner of controlled demolitions" is a collapse theory, not a conspiracy theory.

Charles Clifton: From a momentum point of view, if one floor collapses on another in a building, the force that that floor invokes on the floor below is slightly greater than what the floor below is designed to withstand.

No one has shown that scenario to be valid. Northwestern University's Professor Zdeněk Bažant's analysis necessitates 12 feet of free fall, but that requires explosives to remove all the supporting structure simultaneously. Otherwise, the columns that were not severed would have resisted the downward movement of the upper section and prevented free fall.

Charles Clifton: The first loud bang could have been the top giving way.

A collapse due to column failure would provide a very different audio signature – perhaps a loud "creaking" or "groaning" series of noises, not a huge explosion that was heard and felt by first responders and reporters. An explosion is a much more likely explanation for the first loud bang.

Excellent explosion witness video: http://www.youtube.com/watch?v=wUXGhLrDqb0

For the blast in question, start at:

• 1:43 "We heard a very loud blast explosion. We looked up and the building literally began to collapse before us.
• 1:52 "We heard a loud explosion and at that point the building collapsed"
• 1:56 "At that point we heard a "boom". I looked up and just saw the building coming at us."
• 2:03 Reporter "Do you know if it was an explosion or if it was a building collapse?
• Officer "To me it sounded like an explosion."
• 2:11 "There was another major explosion, the building itself, literally the top of it, came down."
• 2:17 "All of a sudden you hear an explosion, and you could see the building starting to collapse."

Charles Clifton: There were reports of molten steel, but in fact it would have been either molten aluminum, which [melts at] 660 degrees centigrade, or potentially lead from storage batteries, but not steel.

Incorrect: Molten aluminum and lead are silver/gray in daylight conditions. NIST admitted that aluminum glows silvery in daylight, but then speculated that aluminum mixed with organic material would have caused it to glow orange. NIST's speculation has been disproven by subsequent experiments. Even had NIST been correct, the hottest portion of the flow of molten metal was not merely orange but yellow-white – indicating temperatures hot enough to melt steel or iron. The RJ Lee Group stated that iron melted during the event, producing spherical metallic particles. They also stated that lead vaporized during the collapse. Both of these prove temperatures far in excess of what jet fuel or office fires can attain.

 A 21. http://www.nist.gov/el/disasterstudies/wtc/faqs_wtctowers.cfm

NIST and Mr. Clifton are making unsupported assertions. That is not science. They must show by experiment that their hypotheses are valid.

Charles Clifton: The fire itself would have gotten to over 1000 degrees (centigrade).

There is no evidence to support that claim:

Per NIST: "The microstructures of the steels known to have been exposed to fire, based on the pre-collapse photographic evidence ... show no evidence of exposure to temperatures above 600° C for any significant time." NCSTAR 1-3C p. 281

Per NIST: "From the limited number of recovered structural elements, no conclusive evidence was found to indicate that pre-collapse fires were severe enough to have a significant effect on the microstructure that would have resulted in weakening of the steel structure." NCSTAR 1-3C p. 235

Charles Clifton: All I am certain of there is that [the molten metal] wasn't steel.

Clifton gives no evidence to support his certainty. On the contrary, his sweeping denial contradicts established and overwhelming evidence, including the forensic analysis by four independent entities and numerous eyewitnesses of molten metal.

From FEMA BPAT Report, May 2002, Appendix C

Charles Clifton: The initial impact [at the South Tower] had destroyed in the south east corner, and along the east side, some six levels of floors. ... Finally, the perimeter frame along the eastern side failed in an elastic buckling mode over some six stories.

This is incorrect, and again, since the rest of his theory of the South Tower collapse is built on this fallacy, the theory is invalid. Per NIST: "Floors 80 and 81 were damaged by the fuselage between the outside wall and the core. The east floor area between the core and exterior wall was undamaged." NCSTAR 1-2 p. 230.

Charles Clifton: There was another characteristic of the building that made it vulnerable; if you look at the building, you see that that dense network of columns didn't extend around the corners; the corners actually had quite large windows.

Incorrect: The Trade Towers did NOT have windows on the corners. The spandrel panels continued through the 45-degree-chamfered corners.

• http://www.hdwpapers.com/world_trade_center_towers_from_below_wallpaper-wallpapers.html
• http://www.nydailynews.com/new-york/world-trade-center-40th-anniversary-gallery-1.1307674?pmSlide=1.1307658
• http://news.nationalgeographic.com/news/2011/09/pictures/110908-about-911-september-9-11-twin-world-trade-center-towers-indelible/#/september-9-11-attacks-anniversary-ground-zero-world-trade-center-pentagon-flight-93-smoke-tower_40014_600x450.jpg

Charles Clifton: This meant that the east frame was not tied back to the north or south frames at the corners, making it vulnerable to collapse when the floors were destroyed by the impact at the south end of this frame, and the floor-to-frame system degraded by fire at the north end. The loss of lateral support from the floors initiated the buckling collapse.

The East side was clearly tied to the North and South sides via the continuous spandrel panels:

Undicisettembre: What do you think of conspiracy theories which claim that once the upper block started tipping over it should have kept rotating, and [that the fact that it didn't] proves that the towers were intentionally demolished with explosives?

Charles Clifton: That's physically impossible because of the very limited strength of the floor to frame and floor to core connections. To rotate as a rigid body, floors had to remain rigidly attached to the frame and to the core, and there's no way that that could happen. Those connections were never designed to handle anything like that; as soon as the top started to rotate, the floors were torn straight out.

The top 29 floors were falling to one side, not rotating as the question suggests. According to Newton's first law, an object in motion will stay in motion unless acted upon by an unbalanced external force. The top part of the South Tower would have fallen to one side and off. The South Tower would not have collapsed exactly as the North Tower did, with the top part falling almost straight down. In any event, the massive, 29-story upper portion had leaned 22 degrees, yet the structure below developed complete symmetrical destruction all the way down all four sides of the building – in less than 12 seconds – at near free-fall acceleration.

Charles Clifton: So what happened with the substation in WTC 7 is that after the attacks, it was destroyed, but the fuel supply system continued to operate and fed fuel into the fires at substation level. These fires burned for some seven or eight hours and would have progressively weakened at least some of the transfer members.

Incorrect: NIST gave up the diesel fuel fire hypothesis in December of 2007.

Per NIST: "The working hypothesis is based on an initial local failure caused by normal building fires, not by fires from leaking pressurized fuel lines or fuel from day tanks."

http://www.nist.gov/el/disasterstudies/ncst/upload/WTC7_Approach_Summary_18Dec07-Final.pdf

The only place where a diesel fuel fire could have had an effect on the collapse was the generator room in the northeast corner of the 5th floor. An independent researcher noted that in a photograph on page 22 of the FEMA report on WTC 7, there was no smoke coming out of the louvers in the generator room, and that no fire was reported on floor 5 at any time. It was further noted that if the louvers were closed, any fire would have been starved for oxygen and could not have burned hot enough to weaken column 79. In their final report, NIST paraphrased these findings 13 times.

Charles Clifton: So [the girder] was pushed around on its corbel. Probably, while it was being heated, it would also have been pushed into the column as it expanded on heating, while at the same time deflecting downwards, but as the fire started to burn out and cool down in that region, the now deflected girder would start to cool down and reduce in length. This would have led to its falling off the corbel and initiating the collapse.

This is NOT NIST's theory, and, it also doesn't work. The math exposes the problem:

Per NIST, the girder attained a temperature of about 300-350° C (NCSTAR 1-9 Vol.2 p. 528 [pdf p. 190], Figure 11-46. http://www.nist.gov/customcf/get_pdf.cfm?pub_id=861612).

At 350° C, steel still has about 75% of its room-temperature strength. It would not have sagged or shortened much at all. A 53½-foot beam would expand 2.8 inches at 350° C (per the chart below), so the 45-foot girder would have expanded about 2-½ inches. There is about an inch of space at either end of the girder, so the girder would have shortened about ½-inch by bowing downward, which is not anywhere near enough to make it fall off its seat.

AE911Truth's Conclusion: It is apparent, upon review of the numerous inaccurate observations and dismissal of actual facts on the part of Mr. Clifton - that a detailed debate between AE911Truth and him, or any of the dozen or so such licensed engineer supporters of the official conspiracy theory regarding the evidence of the controlled demolition of the three World Trade Center skyscrapers on 9/11 - would greatly benefit the engineering community. We hereby offer such an opportunity to debate competing hypotheses interactively with our architects/engineers in an open forum beginning, as always, with the free-falling seven-second destruction of World Trade Center 7.