TIL - World Trade Center 7

I remember the 9/11 attack being for hours on end on greek TV 16 years ago. I remember being worried about a family friend who lives in Boston and travelled from Greece to America on that day. I remember sitting on the table (I was a child back then, so I was allowed to do so when nobody was watching) and hoping our friend was ok (thankfully she was).

(Image source: commons.wikimedia.org)

A few weeks ago I got a comment to write about another building collapse that happened on that day, hours after the Twin Towers had fallen. The building that was separated from the main block of the World Trade Center Complex, Building 7 (WTC 7). Since it housed offices of the CIA, the Secret Service, the Office of Emergency Management and the Department of Defence, lots of conspiracy theories have been born on the grounds of its mysterious (?) collapse.

I state that I do not wish to support either side or promote a specific version of the story, I am not an expert on the subject. This post addresses to a person who has supported me for a long time during my stay around here and is just a thank you project (I will not accept any payment from them for doing it, although I was suggested to). I just made an investigation, read various articles from differing sites and according to my studying I wrote the text below.

In this post we are not going to analyse the motives or background stories behind the disaster. We're just looking into the two main theories considering why the building finally fell down. The fact that I am not a mechanic means that I cannot explain it in a very thorough way. Based on what I read, this is what I got.

(Image source: commons.wikimedia.org)

The NIST (National Institute of Standards and Technology) report

From the NIST report [6] we get:

The collapse of WTC 7 was the first recorded event of a tall building collapsing because of fire. There were no serious injuries or fatalities since evacuation of the building had started after the plane crashes on WTC 1 and 2.

Debris from the Twin Towers caused WTC 7 to catch fire that fed on office combustibles. Floors 7 to 9 and 11 to 13 were burning for almost 7 hours when the building started to collapse under thermal expansion. Now, you would start wondering how can a fire melt down steel. It seems like the sprinkler system didn't work on that day, owing to the damage from the collapse of the Twin Towers.

Since the fires could not be put out, steel was constantly heating up. And because they were made of thinner SFRM (Sprayed Fire-Resistive Material), floor beams, floor slabs and connections would heat up faster than the steering columns. When temperature exceeds 593 degrees Celsius, steel loses its strength and stiffness. On the east side of the building temperature seemed to have reached, if not exceeded, 600 degrees Celsius, leading to thermal expansion of the steel beams and transferred the damage to other floors.

What seemed to have initiated the domino of destruction was the buckling of column 79, which at the time must have had a temperature of around 400 degrees. As it heated up, it started expanding and as it met resistance from other columns or steel members, it started to buckle. Column 79 buckling led to the collapse of floor 13 that triggered a whole cascade of floor failures all the way down to floor 5 (the other floors were already weakened by the fire damage). Column 79 was left with little lateral support and started to buckle eastward; as the failure continued it transferred to columns 80 and 81, the floors started falling down leaving the exterior eastern quarter of the building nothing more than a hollow shell.

(Image source: commons.wikimedia.org)

Failure started moving westwards. Debris was falling and the load was too heavy for the remaining columns to handle. As a result they started to buckle under the weight of the falling floors. The hollow core was now ready to swallow the rest of the building, which fell on the buckling 5th-14th floors.

The NIST report says that the building would still have fallen down in an event of a fire even if it hadn't had been damaged by the debris from the collapse of WTC 1. There were fires in the southwest and northeast region, but only the latter ones were strong enough to be proven destructive. The theory that diesel fuels enhanced the fires was not proven. There were also no blasts according to audiovisual evidence, moreover a blast would produce 130-140 dB sound at a distance of at least half a mile in an open space, but no such loud noise was recorded or heard by witnesses.

(Image source: commons.wikimedia.org)

A second opinion

There has been another, contradicting, theory that the NIST rejects, the one of controlled demolition. This idea is mainly supported by conspiracy theorists that claim the Bush government planted explosives in order to bring the building down. The symmetrical collapse of the building suggests that explosives went off at the same time, cut through the steel support columns and led to total disaster.

The free fall:
The time it took the building to fall down shows that it collapsed under free fall acceleration (free fall is the undisturbed fall of an object that meets no resistance but the acceleration of gravity). Based on that, it means that either the buckling of the columns happened almost simultaneously (something that many people believe is hard to happen, but having extended fires burning for 7 hours could probably cause that), or explosions were triggered from the upper floors to the lower ones and started creating a hollow pocket to allow the building fall under its own weight.

The building collapsing straight downwards:
The building seemed to collapse in a straight line, something that intrigued conspiracy theorists. If you consider how really tall buildings are made and the standards of their construction, it makes sense that it did not lean over but rather fell right downwards, we don't talk about a tall tree that's hit by a car and falls down or a lean Jenga tower, we're talking about a building that weighs tons and gives away when its steering columns fail to support its weight.

The traces of explosive matter:
Traces of explosive nano-thermite were found in the dust from the ruins, adding another argument for the controlled demolition theory. Professor E. Jones had brought that as evidence of the explosives theory [4], but since some argue [11] that the test beams could have been "contaminated" while being cut, removed from the site and transferred for studying, this idea cannot be cosidered 100% valid. Also, explosion experts did not mention any obvious nano-thermite effects on the remaining columns.

The blasting sounds:
There have been reports of explosion sounds on the grounds of WTC 7, but those explosions were not loud enough to be identified as explosive matter ones. Within the building items like fire extinguishers, gas and electricity lines were consumed by the fires and small scale explosions would unavoidably occur.

The vibrations: No seismographs recorded sudden vibrations moments before the collapse. The organs detected ascending ground activity as the collapse started and then vibrations started to wear off.

It was not hit by the "suicide" planes:
Since no plane crashed into WTC 7, how did it end up to rubble? Well, the debris from the Twin Towers that weighed tons (you do remember how massive those skyscrapers were) and was violently thrown away towards buildings 6 and 7 caused serious damage on them. WTC 7 was severely damaged on its souhwest corner and its south face. The debris and (probably) ruptured diesel tanks of the building initiated the fires.

Steel does not melt by fire:
Steel requires enormous amounts of heat to melt, how could a fire cause an entire building to collapse? The WTC 7 skeleton was made exclusively from steel that after being heated up for 7 hours it started to expand, not melt down completely. As it expanded, it met resistance from the upper floors and started to bulk, leading to the final collapse of the building. Another such example of a steel skeleton building collapsing by fire happened in Tehran (Iran) last January. The video below explains pretty well how can a steel building be affected by fire.

So, long story short:

Debris from the extremely fierce collapse of WTC 1 and 2 fell on buildings 6 and 7. Building 7 gets damaged, fires start burning on low floors (7-9 and 11-13). The fires could not be put out due to little water pressure and burned for about 7 hours. The steel skeleton of the building did not qualify for such long time heat resistance, so the steel started to heat up and expand (like all bodies do when their temperature rises). The design of the building was such (all the main support columns were set to surround it in order to leave more room for open floors) that when a supporting column was weakened enough, a domino of failures was set off starting from the east side to the west as viewed in the video below.

The long burning fires, the architecture of the building, the poor fire extinguishing system seem to be the official general consensus of what brought Building 7 down and added another damage on the list of 9/11 disaster.

Conclusion

Without having any expert knowledge on the matter, I can only take the official explanation as right for now (although there will always be people to doubt it). Such a large scale conspiracy would take a tremendously big number of people taking an oath of silence, which practically would be impossible [14], especially for so many years. If, in the future, this theory proves to be wrong, I will have to reconsider my opinion. But until then, I'll stick to what I got.

Feel free to express your opinions in the comments. I would love to have a further discussion on the matter.