September 11 attacks Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.Anti-spam check. Do not fill this in! === National Institute of Standards and Technology === {{Main|NIST World Trade Center Disaster Investigation}} {{See also|7 World Trade Center#9/11 and collapse}} [[File:WTC-Wreckage-exterior shell of south tower.jpg|thumb|The exterior support columns from the lower level of the South Tower remained standing after the [[Collapse of the World Trade Center|building collapsed]]]] The U.S. [[National Institute of Standards and Technology]] (NIST) investigated the collapses of the Twin Towers and 7{{spaces}}WTC. The investigations examined why the buildings collapsed and what fire protection measures were in place, and evaluated how fire protection systems might be improved in future construction.<ref name="NISTInvest">{{cite press release |title=NIST's World Trade Center Investigation |publisher=National Institute of Standards and Technology |date=September 8, 2006 |url=https://www.nist.gov/news-events/news/2006/09/nists-world-trade-center-investigation |access-date=September 4, 2011}}</ref> The investigation into the collapse of 1{{spaces}}WTC and 2{{spaces}}WTC was concluded in October 2005 and that of 7{{spaces}}WTC was completed in August 2008.<ref name="NIST WTC 7 Investigation">{{cite press release |title=NIST WTC 7 Investigation Finds Building Fires Caused Collapse |date=August 21, 2008 |publisher=The National Institute of Standards and Technology |url=https://www.nist.gov/news-events/news/2008/08/nist-wtc-7-investigation-finds-building-fires-caused-collapse |access-date=September 4, 2011}}</ref> NIST found that the fireproofing on the Twin Towers' steel infrastructures was blown off by the initial impact of the planes and that had this not occurred, the towers likely would have remained standing.<ref name="NISTCollapse">{{cite book|author=National Construction Safety Team |chapter-url=https://www.nist.gov/customcf/get_pdf.cfm?pub_id=909017 |title=Final Report on the Collapse of the World Trade Center Towers |publisher=National Institute of Standards and Technology, United States Department of Commerce |chapter=Executive Summary |date=September 2005 |access-date=April 10, 2011 |chapter-format=PDF}}</ref> A 2007 study of the north tower's collapse published by researchers of [[Purdue University]] determined that since the plane's impact had stripped off much of the structure's thermal insulation, the heat from a typical office fire would have softened and weakened the exposed girders and columns enough to initiate the collapse regardless of the number of columns cut or damaged by the impact.<ref>{{cite journal|last1=Irfanoglu |first1=A.|last2=Hoffmann |first2=C. M.|doi=10.1061/(ASCE)0887-3828(2008)22:1(62)|title=Engineering Perspective of the Collapse of WTC-I|journal=Journal of Performance of Constructed Facilities|volume=22|page=62|year=2008|quote=As the aircraft debris went through several stories in the tower, much of the thermal insulation on the core columns would have been scoured off. Under such conditions, the ensuing fire would be sufficient to cause instability and initiate collapse. From an engineering perspective, impact damage to the core structure had a negligible effect on the critical thermal load required to initiate collapse in the core structure.}}</ref><ref>{{cite news|title=Purdue creates scientifically based animation of 9/11 attack|last=Tally|first=Steve|publisher=Purdue News Service|url=http://news.uns.purdue.edu/x/2007a/070612HoffmannWTC.html|date=June 12, 2007|access-date=September 4, 2011|quote=The aircraft moved through the building as if it were a hot and fast lava flow", Sozen says. "Consequently, much of the fireproofing insulation was ripped off the structure. Even if all of the columns and girders had survived the impact{{snd}}an unlikely event{{snd}}the structure would fail as the result of a buckling of the columns. The heat from an ordinary office fire would suffice to soften and weaken the unprotected steel. Evaluation of the effects of the fire on the core column structure, with the insulation removed by the impact, showed that collapse would follow whatever the number of columns cut at the time of the impact.|archive-date=December 31, 2018|archive-url=https://web.archive.org/web/20181231084252/https://news.uns.purdue.edu/x/2007a/070612HoffmannWTC.html|url-status=dead}}</ref> The director of the original investigation stated that "the towers did amazingly well. The terrorist aircraft didn't bring the buildings down; it was the fire that followed. It was proven that you could take out two-thirds of the columns in a tower and the building would still stand".<ref name="TerrorProof">{{cite web|title=Building a Terror-Proof Skyscraper: Experts Debate Feasibility, Options |first=Pete |last=Sigmund |url=http://www.constructionequipmentguide.com/Building-a-Terror-Proof-Skyscraper-Experts-Debate-Feasibility-Options/2598/ |access-date=April 11, 2012 |date=September 25, 2002}}</ref> The fires weakened the trusses supporting the floors, making the floors sag. The sagging floors pulled on the exterior steel columns causing the exterior columns to bow inward. With the damage to the core columns, the buckling exterior columns could no longer support the buildings, causing them to collapse. Additionally, the report found the towers' stairwells were not adequately reinforced to provide adequate [[Fire escape|emergency escape]] for people above the impact zones.<ref name="NIST">{{cite web|title=Translating WTC Recommendations into Model Building Codes|publisher=National Institute of Standards and Technology|url=http://wtc.nist.gov/NIBS_MMC/CodeChangeProposals.htm|archive-url=https://web.archive.org/web/20110310004023/http://wtc.nist.gov/NIBS_MMC/CodeChangeProposals.htm|archive-date=March 10, 2011|access-date=September 4, 2011 |date=October 25, 2007}}</ref> NIST concluded that uncontrolled fires in 7{{spaces}}WTC caused floor beams and girders to heat and subsequently "caused a critical support column to fail, initiating a fire-induced progressive collapse that brought the building down".<ref name="NIST WTC 7 Investigation" /> Summary: Please note that all contributions to Christianpedia may be edited, altered, or removed by other contributors. 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