Collapse of 7 World Trade Center

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Collapse of 7 World Trade Center

7 World Trade Center on fire after the collapse of the Twin Towers on 9/11
7 World Trade Center on fire after the collapse of the Twin Towers on 9/11

September 11, 2001

As the North Tower collapsed on September 11, 2001, debris hit 7 World Trade Center, damaging the south face of the building and igniting fires. The bottom portion of the building's south face was heavily damaged from debris, including: damage to the southwest corner from the 8th to 18th floor, a large vertical gash on the center-bottom extending at least ten floors, and other damage as high as the 18th floor.[1]

Debris from the collapse of the North and South Towers
Debris from the collapse of the North and South Towers


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.[2] A massive fire 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.[3][4] During the afternoon, fire was also seen on floors 6–10, 13–14, 19–22, and 29–30.[1] At approximately 2:00 p.m., firefighters noticed a bulge in the southwest corner of 7 World Trade Center between the 10 and 13th floors which was a sign that the building was unstable and might collapse.[5] During the afternoon, firefighters also heard creaking sounds coming from the building.[6] Around 3:30 pm, given that 7 World Trade Center was unstable and would possibly collapse, 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.[7][5] At 5:20 p.m. EDT on September 11, 2001, 7 World Trade Center collapsed. The building had been evacuated and there were no casualties associated with the collapse.

Video of the collapse

Initial expert opinion

7 World Trade Center housed an ($13 million) emergency command center on the 23rd floor that was used by the mayor. A diesel fuel tank, which stored 6,000 gallons of fuel, was located above ground in the building to supply emergency power to the command center, in event of a power failure. In 1998 and 1999, the Fire Department had warned the city of the fire hazards posed by the fuel tank, saying that if it leaked and caught fire, it would cause a "disaster." Oftentimes, fuel tanks are placed below ground for safety reasons, to protect it from falling debris and the building from leaks.[8]

“ At least two firefighters who were at the scene, Deputy Chief James Jackson and Battalion Chief Blaich, said that the southwest corner of the building near the fuel tank was severely damaged, possibly by falling debris, and that the tank might have been breached. Mr. Jackson said that about an hour before the building's collapse, heavy black smoke, consistent with a fuel fire of some sort, was coming from that part of the building.[9] ”

Additional fuel tanks used by other tenants were located below ground.

Regarding the possible role of the fuel tanks in the collapse:

“ "If the enclosures were damaged, then yes, this would be enough fuel to explain why the building collapsed," Dr. Barnett said... If further studies of the debris confirm the findings of extremely high temperature, Dr. Barnett said, "the smoking gun would be the fuel." Others experts agreed that the diesel fuel could have speeded the collapse, but said the building might have met the same fate simply because of how long it burned. "The fuel absolutely could be a factor," said Silvian Marcus, executive vice president for the Cantor Seinuk Group and a structural engineer involved in the original design of the building, which was completed in 1987. But he added, "The tanks may have accelerated the collapse, but did not cause the collapse." ”

About falling debris:

“ Falling debris also caused major structural damage to the building, which soon began burning on multiple floors, said Francis X. Gribbon, a spokesman for the Fire Department. By 11:30 a.m., the fire commander in charge of that area, Assistant Chief Frank Fellini, ordered firefighters away from it for safety reasons. A combination of an uncontrolled fire and the structural damage might have been able to bring the building down, some engineers said. But that would not explain steel members in the debris pile that appear to have been partly evaporated in extraordinarily high temperatures, Dr. Barnett said. "Any structure anywhere in the world, if you put it in these conditions, it will not stand, Mr. Marcus said. The buildings are not designed to be a torch." ”

FEMA study

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. Structural elements were exposed to high temperatures for a sufficient period of time to reduce their strength to the point of collapse.[10]

The report did not reach final conclusions about the cause of the collapse, but listed several issues requiring further investigation. FEMA made these findings:

Loss of structural integrity was likely a result of weakening caused by fires on the 5th to 7th floors. The specifics of the fires in WTC 7 and how they caused the building to collapse remain unknown at this time. Although the total diesel fuel on the premises contained massive potential energy, the best hypothesis has only a low probability of occurrence. Further research, investigation, and analyses are needed to resolve this issue. [Ch. 5, p. 31.]
Plan view of collapse progression, with structural failure initiating on lower floors, on the east side of the building and vertical progression up to the east mechanical penthouse
Plan view of collapse progression, with structural failure initiating on lower floors, on the east side of the building and vertical progression up to the east mechanical penthouse

NIST investigation

In response to FEMA's concerns, the Commerce Department’s National Institute of Standards and Technology (NIST) was authorized to lead a three-year, $16 million investigation into the structural failure and collapse of the World Trade Center twin towers and 7 World Trade Center.[11] The investigation, led by Dr S. Shyam Sunder, drew not only upon in-house technical expertise, but also 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).[12]

Few photos and video clips exist that show the damage sustained to south face of 7 World Trade Center on 9/11. From a news helicopter, ABC News captured footage of the south face of 7 World Trade Center, including a glimpse of a gash, extending approximately 10 stories
Few photos and video clips exist that show the damage sustained to south face of 7 World Trade Center on 9/11. From a news helicopter, ABC News captured footage of the south face of 7 World Trade Center, including a glimpse of a gash, extending approximately 10 stories

NIST has released a video and still-photo analysis of 7 World Trade Center before its collapse that appears to indicate a greater degree of structural damage from falling debris than originally assumed by FEMA. Specifically, NIST's interim report on 7 World Trade Center displays photographs of the southwest façade of the building that show it to have significant damage. The report also highlights a 10-story gash in the center of the south façade, toward the bottom, extending approximately a quarter of the way into the interior.[13][1] A unique aspect of the design of 7 World Trade Center was that each outer structural column was responsible for supporting 2,000 sq ft (186 m²) of floor space, suggesting that the simultaneous removal of a number of columns severely compromised the structure's integrity.[14] Consistent with this theory, news footage shows cracking and bowing of the building's east wall immediately before the collapse, which began at the penthouse floors.[1] In video of the collapse, taken from the north by CBS News and other news media, the first visible sign of collapse is movement in the east penthouse 8.2 seconds before the north wall began to collapse, which took at least another 7 seconds.[1][15]

A progress report was released in June 2004, outlining NIST's working hypothesis.[16][1] The hypothesis, which was reiterated in a June 2007 status update, is that an initial failure in a critical column occurred below the 13th floor, caused by damage from fire and/or debris induced structural damage of a critical column, from the collapse of the two main towers. The collapse progressed vertically up to the east mechanical penthouse. The interior structure was unable to handle the redistributed load, resulting in horizontal progression of the failure across lower floors, particularly the 5th to 7th floors. This resulted in "a disproportionate collapse of the entire structure."[17]

NIST anticipates the release of a draft report of 7 World Trade Center by the end of 2007.[17] The NIST is utilizing ANSYS to model events leading up to collapse initiation and LS-DYNA models to simulate the global response to initiating events.[18] The investigation of 7 World Trade Center has been 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.[19] Regarding the investigation of 7 World Trade Center, Dr S. Shyam Sunder stated in a New York magazine interview in March 2006, "We are studying the horizontal movement east to west, internal to the structure, on the fifth to seventh floors”; he then added, "But truthfully, I don’t really know. We’ve had trouble getting a handle on Building No. 7."[20] In June 2007, he 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 WTC 7 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."[17]

Damage to adjacent buildings

When 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 is not salvageable. As of August 2007, Fiterman Hall is undergoing deconstruction.[21] The adjacent Verizon Building, an art deco building constructed in 1926, had extensive damage to its east façade from the collapse of 7 World Trade Center, though was able to be restored at a cost of US$1.4 billion.[22]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Interim Report on WTC 7 (pdf). Appendix L. National Institute of Standards and Technology (2004). Retrieved on 2007-08-20.
  2. ↑ Oral Histories From Sept. 11 - Interview with Captain Anthony Varriale (pdf). The New York Times (December 12, 2001). Retrieved on 2007-08-22.
  3. ↑ Spak, Steve. (2001, September 11). WTC 9-11-01 Day of Disaster [Video]. New York City: Spak, Steve.
  4. ↑ Scheuerman, Arthur (December 8, 2006). "The Collapse of Building 7" (pdf). NIST. Retrieved on 2007-06-29.
  5. ↑ 5.0 5.1 WTC: This Is Their Story, Interview with Chief Peter Hayden. Firehouse.com (September 9, 2002). Retrieved on 2007-06-28.
  6. ↑ WTC: This Is Their Story, Interview with Captain Chris Boyle. Firehouse.com (August 2002). Retrieved on 2007-08-22.
  7. ↑ Oral Histories From Sept. 11 - Interview with Chief Daniel Nigro. The New York Times (October 24, 2001). Retrieved on 2007-06-28.
  8. ↑ Glanz, James and Eric Lipton. "City Had Been Warned of Fuel Tank at 7 World Trade Center", The New York Times, December 20, 2001.
  9. ↑ Glanz, James and Eric Lipton. "City Had Been Warned of Fuel Tank at 7 World Trade Center", The New York Times, December 20, 2001.
  10. ↑ WTC7 - Building Performance Study. FEMA (May 2002).
  11. ↑ NIST’s World Trade Center Investigation. NIST. Retrieved on 2007-08-20.
  12. ↑ Final Report on the Collapse of the World Trade Center (pdf). National Institute of Standards and Technology (NIST) (September 2005).
  13. ↑ "Debunking the 9/11 Myths: Special Report", Popular Mechanics, March 2005.
  14. ↑ NIST Response to the World Trade Center Disaster (Part IIC - WTC 7 Collapse) (pdf). NIST (April 5, 2005). Retrieved on 2007-08-23.
  15. ↑ CBS News. (2001, September 11). CBS Sept. 11, 2001 4:51 pm - 5:33 pm (September 11, 2001) [Television]. WUSA, CBS 9, Washington, D.C..
  16. ↑ Key Findings of NIST’s June 2004 Progress Report on the Federal Building and Fire Safety Investigation of the World Trade Center Disaster. Fact sheets from NIST. National Institute of Standards and Technology (2004). Retrieved on 2006-07-28.
  17. ↑ 17.0 17.1 17.2 National Institute of Standards and Technology (June 29, 2007). NIST Status Update on World Trade Center 7 Investigation. Press release.
  18. ↑ McAllister, Therese (December 12, 2006). WTC 7 Technical Approach and Status Summary. NIST.
  19. ↑ Answers to Frequently Asked Questions. National Institute of Standards and Technology (August 2006).
  20. ↑ Mark Jacobson (March 2006). The Ground Zero Grassy Knoll. New York Magazine. Retrieved on 2006-11-26.
  21. ↑ Fiterman Hall - Project Updates. Lower Manhattan Construction Command Center/LMDC. Retrieved on 2007-08-23.
  22. ↑ Verizon Building Restoration. New York Construction (McGraw Hill). Retrieved on 2007-06-28.

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