User:Tom harrison/7wtc-collapse-draft: Difference between revisions

=== 9/11 and collapse ===

As the North Tower collapsed on September 11, 2001, heavy debris hit 7&nbsp;World Trade Center, causing damage to the south face of the building.<ref name="NIST-june2004"/> 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. <ref name="ncstar1-a">{{cite book |url=http://wtc.nist.gov/NCSTAR1/PDF/NCSTAR%201A.pdf |format=PDF| publisher=NIST |title=NIST NCSTAR1-A: Final Report on the Collapse of World Trade Center Building 7 |month=November | year=2008 |accessdate=July 11, 2011}}</ref> The building was equipped with a [[Fire sprinkler system|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.<ref>{{cite web |url=http://wtc.nist.gov/media/P4InvestigationofActiveFireProtection.pdf|format=PDF |title=Active Fire Protection Systems Issues |author=Grosshandler, William |publisher=NIST |accessdate=September 11, 2007}}</ref><ref>{{cite web |url=http://wtc.nist.gov/NCSTAR1/PDF/NCSTAR%201-4.pdf |format=PDF|title=Active Fire Protection Systems |author=Evans, David D |publisher=NIST |month=September | year=2005 |accessdate=August 26, 2010}}</ref>

After the North Tower collapsed, some firefighters entered 7&nbsp;World Trade Center to search the building. They attempted to extinguish small pockets of fire, but low water pressure hindered their efforts.<ref>{{cite web |url=http://graphics8.nytimes.com/packages/pdf/nyregion/20050812_WTC_GRAPHIC/9110313.PDF |format=PDF|title=Oral Histories From Sept.&nbsp;11 – Interview with Captain Anthony Varriale |work=The New York Times |date=December 12, 2001 |accessdate=August 22, 2007}}</ref> Fires burned into the afternoon on the 11th and 12th floors of 7&nbsp;World Trade Center, the flames visible on the east side of the building.<ref>{{cite video | people=Spak, Steve | date=September 11, 2001 | url=http://video.google.com/videoplay?docid=6790722824543352916&hl=en | title=WTC 9-11-01 Day of Disaster | medium=Video | location=New York City | publisher=Spak, Steve}}</ref><ref>{{cite journal |author=Scheuerman, Arthur |url=http://wtc.nist.gov/media/ScheuermanStatementDec2006.pdf |format=PDF |title=The Collapse of Building 7 |date=December 8, 2006 |publisher=NIST |accessdate=June 29, 2007}}</ref> During the afternoon, fire was also seen on floors 6–10, 13–14, 19–22, and 29–30.<ref name="NIST-june2004"/> In particular, the fires on floors 7 through 9 and 11 through 13 continued to burn out of control during the afternoon.<ref name="nist-questions">{{cite web |url=http://www.nist.gov/public_affairs/factsheet/wtc_qa_082108.cfm |title=Questions and Answers about the NIST WTC 7 Investigation |publisher=NIST |accessdate=August 26, 2010}}</ref> At approximately 2:00&nbsp;pm, firefighters noticed a bulge in the southwest corner of 7&nbsp;World Trade Center between the 10th and 13th floors, a sign that the building was unstable and might collapse.<ref name="hayden">{{cite web |url=http://www.firehouse.com/stateprovince/new-york/deputy-chief-peter-hayden |title=WTC: This Is Their Story, Interview with Chief Peter Hayden |publisher=Firehouse.com |date=September 9, 2002 |accessdate=March 3, 2011}}</ref> During the afternoon, firefighters also heard creaking sounds coming from the building.<ref>{{cite web |url=http://www.firehouse.com/stateprovince/new-york/captain-chris-boyle |title=WTC: This Is Their Story, Interview with Captain Chris Boyle |publisher=Firehouse.com |month=August | year=2002 |accessdate=March 3, 2011}}</ref> Around 3:30&nbsp;pm FDNY Chief Daniel Nigro decided to halt rescue operations, surface removal, and searches along the surface of the debris near 7&nbsp;World Trade Center and evacuate the area due to concerns for the safety of personnel.<ref>{{cite news |url=http://www.nytimes.com/packages/html/nyregion/20050812_WTC_GRAPHIC/Nigro_Daniel.txt |title=Oral Histories From Sept.&nbsp;11 – Interview with Chief Daniel Nigro |work=The New York Times |date=October 24, 2001 |accessdate=June 28, 2007}}</ref> At 5:20:33&nbsp;pm EDT on September 11, 2001, 7&nbsp;World Trade Center started to collapse, with the crumble of the east mechanical penthouse, while at 5:21:10&nbsp;pm EDT the entire building collapsed completely.<ref name="fema-ch5"/> There were no [[casualty (person)|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&nbsp;WTC and 2&nbsp;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. According to FEMA, structural elements were exposed to high temperatures for a sufficient period of time to reduce their strength to the point of collapse;<ref name="fema-ch5"/> nevertheless, it has since been determined that the fires burned out in 20 minutes at any given location as they moved from point to point.<ref name="NIST Advisory Committee Dec 2007"/>

The report did not reach conclusions about the cause of the collapse and called for further investigation:

<blockquote>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&nbsp;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.]<ref name="fema-ch5"/></blockquote>

In its progress report, NIST released a video and still-photo analysis of 7&nbsp;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&nbsp;World Trade Center displays photographs of the southwest facade of the building that show it to have significant damage. The report also highlights a 10-story gash in the center of the south facade, toward the bottom, extending approximately a quarter of the way into the interior.<ref name="NIST-june2004"/><ref>{{cite news |url=http://www.popularmechanics.com/technology/military_law/1227842.html?page=5#wtc7 |title=Debunking the 9/11 Myths: Special Report |publisher=Popular Mechanics |date=March 2005|accessdate=January 17, 2008}}</ref> A unique aspect of the design of 7&nbsp;World Trade Center was that each outer structural column was responsible for supporting 2,000&nbsp;sq&nbsp;ft (186&nbsp;m²) of floor space, suggesting that the simultaneous removal of a number of columns severely compromised the structure's integrity.<ref>{{cite web |url=http://wtc.nist.gov/pubs/WTC%20Part%20IIC%20-%20WTC%207%20Collapse%20Final.pdf |format=PDF|title=NIST Response to the World Trade Center Disaster (Part IIC – WTC 7 Collapse) |date=April 5, 2005 |publisher=NIST |accessdate=August 23, 2007}}</ref> 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.<ref name="NIST-june2004"/> 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&nbsp;seconds before the north wall began to collapse, which took at least another 7&nbsp;seconds.<ref name="NIST-june2004"/><ref>{{cite video |url=http://www.archive.org/details/cbs200109111651-1733 |people=CBS News |date=September 11, 2001 |title=CBS Sept.&nbsp;11, 2001 4:51&nbsp;pm – 5:33&nbsp;pm (September 11, 2001) |publisher=[[WUSA (TV)|WUSA]], CBS 9, Washington, D.C |medium=Television}} – View [http://www.youtube.com/watch?v=4k6GMddY-lQ footage] of the collapse captured by CBS</ref>

The working hypothesis, released in the June 2004 progress report and reiterated in a June 2007 status update, was that an initial failure in a critical column occurred below the 13th floor, caused by damage from fire and/or debris 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."<ref name="NIST-june2004"/><ref name="NIST7STAT1"/><ref>{{cite web | year = 2004 |url = http://www.nist.gov/public_affairs/factsheet/wtc_keyfindings.cfm | title = Key Findings of NIST’s June 2004 Progress Report on the Federal Building and Fire Safety Investigation of the World Trade Center Disaster | work=Fact sheets from NIST | publisher=National Institute of Standards and Technology |accessdate =August 26, 2010}}</ref>

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.<ref name="nist-questions" />