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9/11 and collapse

As the North Tower collapsed on September 11, 2001, heavy debris hit 7 World Trade Center, causing damage to the south face of the building. Structural damage occurred to the southwest corner between Floors 7 and 17 and on the south face between Floor 44 and the roof; other possible structural damage includes a large vertical gash near the center of the south face between Floors 24 and 41. The building was equipped with a sprinkler system, but had many single-point vulnerabilities for failure: the sprinkler system required manual initiation of the electrical fire pumps, rather than being a fully automatic system; the floor-level controls had a single connection to the sprinkler water riser; and the sprinkler system required some power for the fire pump to deliver water. Also, water pressure was low, with little or no water to feed sprinklers.

After the North Tower collapsed, some firefighters entered 7 World Trade Center to search the building. They attempted to extinguish small pockets of fire, but low water pressure hindered their efforts. Fires burned into the afternoon on the 11th and 12th floors of 7 World Trade Center, the flames visible on the east side of the building. During the afternoon, fire was also seen on floors 6–10, 13–14, 19–22, and 29–30. In particular, the fires on floors 7 through 9 and 11 through 13 continued to burn out of control during the afternoon. At approximately 2:00 pm, firefighters noticed a bulge in the southwest corner of 7 World Trade Center between the 10th and 13th floors, a sign that the building was unstable and might collapse. During the afternoon, firefighters also heard creaking sounds coming from the building. Around 3:30 pm FDNY Chief Daniel Nigro decided to halt rescue operations, surface removal, and searches along the surface of the debris near 7 World Trade Center and evacuate the area due to concerns for the safety of personnel. At 5:20:33 pm EDT on September 11, 2001, 7 World Trade Center started to collapse, with the crumble of the east mechanical penthouse, while at 5:21:10 pm EDT the entire building collapsed completely. There were no casualties associated with the collapse.

In May 2002, the Federal Emergency Management Agency (FEMA) issued a report on the collapse based on a preliminary investigation conducted jointly with the Structural Engineering Institute of the American Society of Civil Engineers under leadership of Dr. W. Gene Corley, P.E. FEMA made preliminary findings that the collapse was not primarily caused by actual impact damage from the collapse of 1 WTC and 2 WTC but by fires on multiple stories ignited by debris from the other two towers that continued unabated due to lack of water for sprinklers or manual firefighting. The report did not reach conclusions about the cause of the collapse and called for further investigation.

In response to FEMA's concerns, the National Institute of Standards and Technology (NIST) was authorized to lead an investigation into the structural failure and collapse of the World Trade Center twin towers and 7 World Trade Center. The investigation, led by Dr S. Shyam Sunder, drew not only upon in-house technical expertise, but also upon the knowledge of several outside private institutions, including the Structural Engineering Institute of the American Society of Civil Engineers (SEI/ASCE), the Society of Fire Protection Engineers (SFPE), the National Fire Protection Association (NFPA), the American Institute of Steel Construction (AISC), the Council on Tall Buildings and Urban Habitat (CTBUH), and the Structural Engineers Association of New York (SEAoNY).

The bulk of the investigation of 7 World Trade Center was delayed until after reports were completed on the collapse of the World Trade Center twin towers. In the meantime, NIST provided a preliminary report about 7 World Trade Center in June 2004, and after that released occasional updates on the investigation. According to NIST, the investigation of 7 World Trade Center was delayed for a number of reasons, including that NIST staff who had been working on 7 World Trade Center were assigned full-time from June 2004 to September 2005 to work on the investigation of the collapse of the twin towers. In June 2007, Shyam Sunder explained, "We are proceeding as quickly as possible while rigorously testing and evaluating a wide range of scenarios to reach the most definitive conclusion possible. The 7 WTC investigation is in some respects just as challenging, if not more so, than the study of the towers. However, the current study does benefit greatly from the significant technological advances achieved and lessons learned from our work on the towers."

In November, 2008, NIST released its final report on the causes of the collapse of 7 World Trade Center. This followed their August 21, 2008 draft report which included a period for public comments. In its investigation, NIST utilized ANSYS to model events leading up to collapse initiation and LS-DYNA models to simulate the global response to the initiating events. NIST determined that diesel fuel did not play an important role, nor did the structural damage from the collapse of the twin towers, nor did the transfer elements (trusses, girders, and cantilever overhangs). But the lack of water to fight the fire was an important factor. The fires burned out of control during the afternoon, causing floor beams near Column 79 to expand and push a key girder off its seat, triggering the floors to fail around column 79 on Floors 8 to 14. With a loss of lateral support across nine floors, Column 79 soon buckled - pulling the East penthouse and nearby columns down with it. With the buckling of these critical columns, the collapse then progressed east-to-west across the core, ultimately overloading the perimeter support, which buckled between Floors 7 and 17, causing the entire building above to fall downward as a single unit. The fires, fueled by office contents, along with the lack of water, were the key reasons for the collapse.

When the first 7 World Trade Center collapsed, debris caused substantial damage and contamination to the Borough of Manhattan Community College's Fiterman Hall building, located adjacent at 30 West Broadway, to the extent that the building was not salvageable. In August 2007, Fiterman Hall was scheduled for deconstruction. A revised plan called for demolition in 2009 and completion of the new Fiterman Hall in 2012, at a cost of $325 million. The adjacent Verizon Building, an art deco building constructed in 1926, had extensive damage to its east facade from the collapse of 7 World Trade Center, though it was able to be restored at a cost of US$1.4 billion.

7 World Trade Center housed SEC files relating to numerous Wall Street investigations, as well as other federal investigative files. All the files for approximately 3,000 to 4,000 SEC cases were destroyed. While some were backed up in other places, others were not, especially those classified as confidential. Files relating Citigroup to the WorldCom scandal were lost. The Equal Employment Opportunity Commission estimates over 10,000 cases will be affected. The Secret Service had its largest field office, with more than 200 employees, in WTC 7 and lost investigative files. Says one agent: “All the evidence that we stored at 7 World Trade, in all our cases, went down with the building.”

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World Trade Center controlled demolition conspiracy theories say that the buildings that collapsed on September 11, including building seven, were felled by controlled demolition. The draft NIST report rejected this hypothesis, as the window breakages and blast sound that would have occurred if explosives were used were not observed.

The collapse of the old 7 World Trade Center is remarkable because it was the first known instance of a tall building collapsing primarily as a result of uncontrolled fires. Based on its investigation, NIST reiterated several recommendations it had made in its earlier report on the collapse of the twin towers, and urged immediate action on a further recommendation: that fire resistance should be evaluated under the assumption that sprinklers are unavailable; and that the effects of thermal expansion on floor support systems be considered. Recognizing that current building codes are drawn to prevent loss of life rather than building collapse, the main point of NIST's recommendations is that buildings should not collapse from fire even if sprinklers are unavailable.

Citations defined elsewhere:

1. ^ "Interim Report on WTC 7" (PDF). Appendix L. National Institute of Standards and Technology. 2004. Retrieved August 20, 2007.
2. ^ NIST NCSTAR1-A: Final Report on the Collapse of World Trade Center Building 7 (PDF). NIST. 2008. Retrieved July 11, 2011. {{cite book}}: Unknown parameter |month= ignored (help)
3. Grosshandler, William. "Active Fire Protection Systems Issues" (PDF). NIST. Retrieved September 11, 2007.
4. Evans, David D (2005). "Active Fire Protection Systems" (PDF). NIST. Retrieved August 26, 2010. {{cite web}}: Unknown parameter |month= ignored (help)
5. "Oral Histories From Sept. 11 – Interview with Captain Anthony Varriale" (PDF). The New York Times. December 12, 2001. Retrieved August 22, 2007.
6. Spak, Steve (September 11, 2001). WTC 9-11-01 Day of Disaster (Video). New York City: Spak, Steve.
7. Scheuerman, Arthur (December 8, 2006). "The Collapse of Building 7" (PDF). NIST. Retrieved June 29, 2007. {{cite journal}}: Cite journal requires |journal= (help)
8. ^ "Questions and Answers about the NIST WTC 7 Investigation". NIST. Retrieved August 26, 2010.
9. "WTC: This Is Their Story, Interview with Chief Peter Hayden". Firehouse.com. September 9, 2002. Retrieved March 3, 2011.
10. "WTC: This Is Their Story, Interview with Captain Chris Boyle". Firehouse.com. 2002. Retrieved March 3, 2011. {{cite web}}: Unknown parameter |month= ignored (help)
11. "Oral Histories From Sept. 11 – Interview with Chief Daniel Nigro". The New York Times. October 24, 2001. Retrieved June 28, 2007.
12. ^ Gilsanz, Ramon, Edward M. DePaola, Christopher Marrion, and Harold "Bud" Nelson (2002). "WTC7 (Chapter 5)". World Trade Center Building Performance Study (PDF). FEMA. Retrieved February 17, 2008. {{cite book}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
13. CBS News (September 11, 2001). CBS Sept. 11, 2001 4:51 pm – 5:33 pm (September 11, 2001) (Television). WUSA, CBS 9, Washington, D.C. – View footage of the collapse captured by CBS
14. ^ National Construction Safety Team Advisory Committee. "Transcript: Meeting of the National Construction Safety Team Advisory Committee, December 18, 2007" (PDF).
15. "NIST's World Trade Center Investigation". NIST. Retrieved August 26, 2010.
16. "Final Report on the Collapse of the World Trade Center Towers" (PDF). National Institute of Standards and Technology (NIST). 2005. Retrieved August 26, 2010. {{cite web}}: Unknown parameter |month= ignored (help)
17. "Answers to Frequently Asked Questions". National Institute of Standards and Technology. 2006. Retrieved February 17, 2008. {{cite web}}: Unknown parameter |month= ignored (help)
18. Newman, Michael (June 29, 2007). "NIST Status Update on World Trade Center 7 Investigation" (Press release). National Institute of Standards and Technology. Retrieved August 26, 2010.
19. McAllister, Therese (December 12, 2006). "WTC 7 Technical Approach and Status Summary" (PDF). NIST. Retrieved February 17, 2008.
20. "Fiterman Hall — Project Updates". Lower Manhattan Construction Command Center/LMDC. Retrieved August 23, 2007.
21. Fiterman is Funded BMCC News, November 17, 2008
22. Agovino T Ground Zero building to be razed Crain's New York Business November 13, 2008
23. "Verizon Building Restoration". New York Construction (McGraw Hill). Retrieved June 28, 2007.
24. "SEC & EEOC: Attack Delays Investigations". New York Lawyer. September 17, 2001. Retrieved July 9, 2008.
25. "Citigroup Facing Subpoena in IPO Probe". The Street. Retrieved July 9, 2008.
26. "Federal Agencies: Re-Creating Lost Files". New York Lawyer. September 14, 2001. Retrieved July 9, 2008.
27. "Ground Zero for the Secret Service". July 23, 2002. Retrieved July 9, 2008.
28. Sullivan, Will (September 3, 2006). "Viewing 9/11 From a Grassy Knoll". U.S. News & World Report. Retrieved February 17, 2008.
29. "The evolution of a conspiracy theory". BBC News. July 4, 2008. Retrieved July 4, 2008.
30. Asquith, Christina (2006). "Conspiracies continue to abound surrounding 9/11: on the eve of the fifth anniversary, a group of professors say the attacks were an "inside job."". Diverse Issues in Higher Education: 12. Retrieved July 4, 2008. {{cite journal}}: Unknown parameter |month= ignored (help)
31. "WTC 7 Collapse". Popular Mechanics. 2005. Retrieved July 9, 2008. {{cite web}}: Unknown parameter |month= ignored (help)
32. "Final Report on the Collapse of World Trade Center Building 7 – Draft for Public Comment" (PDF). NIST. 2008. pp. 22–3. {{cite web}}: Unknown parameter |month= ignored (help)