Quote from ByLoSellHi:
No. Building 7 wasn't impacted by a jet, which was 'a' cause, nor exposed to the temperatures generated by jet fuel, which were alleged causes of the reasons the other two buildings fell.
Building 7 essentially is claimed to have fallen in upon itself due to conventional fires burning on multiple floors. SO, yes, it is the first steel skyscraper to have ever been alleged to have been fallen by conventional fires. Even the government concedes this.
Historical Survey of Multistory Building Collapses Due to Fire
By: Jesse Beitel and Nestor Iwankiw, Ph.D., P.E.
INTRODUCTION
There have been, and remain to be, continuing concerns about the adequacy of structural fire protection in the wake of the 9/11 tragedies. As significant as these events were, they were also clearly not representative of the normal accidental impact of fire on building structures. To assess the extent and nature of structural collapses due to fire in taller buildings, a review of existing information about fire incidents resulting in structural collapse was collected and reviewed.
The survey was international in scope and included building collapses due to fire in structures with four or more stories that had occurred during the 1970-2002 time frame of the survey. Both total and partial collapses were included in the survey. Since no database exists that systematically identifies building collapses due to fire (including the NFIRS system), the survey was necessarily exploratory. The survey methodology included a review of both news sources and technical literature, as well as inter-views with a wide range of individuals knowledgeable in structural fire protection. Twenty-two fires were identified that caused either partial or total collapse of a multistory structure. The adequacy and code compliance of the original structural and fire-resistant design of the identified buildings were beyond the scope of the project and were not assessed. While the number of fire events may appear low (average of one/year), these fire events are high-consequence occurrences with respect to loss of life, injuries, and economic costs.
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This survey of structural building collapses due to fire causes was sponsored in 2002 by the National Institute of Standards and Technology (NIST) as part of a larger project. The complete report is available from NIST.1
SURVEY RESULTS
For the purposes of this NIST survey, multistory buildings were defined as those having four or more stories. Nonbuilding structures, such as tunnels, bridges, observation or transmission towers, were not included. Either partial or total failure of the structural framing, members, and/or connections was considered to have constituted a collapse, and it was necessary for a fire to have been the direct cause of this failure.
A total of 22 such cases were identified through 2002 after extensive searches of the literature, news, and other contacts, with the Sept. 11 disasters in New York and Washington, DC, counting as five of these incidents [World Trade Center (WTC) 1, 2, 5, and 7, and the Pentagon]. The cases occurred not only in the U.S. and North America, but also internationally. This NIST survey data demonstrated that buildings of all types of construction and occupancies, in the U.S., North America, and abroad, are susceptible to fires, particularly older buildings and those that may be undergoing construction, renovations, or repairs. The total fatalities were dominated by the Sept. 11 WTC disasters, which were unique in that they were precipitated by terrorist attacks that substantially damaged the buildings' structural framing and destroyed their fire protection systems prior to the fires.
The NIST survey of 22 fire-induced building collapses from 1970-20021 identified a variety of conditions, materials, locations, and buildings. Fifteen cases were from the U.S., two from Canada, and five from Europe, Russia, and South America. The numbers of fire collapse events can be categorized by building material as follows:
Concrete: 7 (1 in Pentagon 9-11 event)
Structural steel: 6 (4 in 9-11 WTC events)
Brick/Masonry: 5
Wood: 2
Unknown: 2
Three of the these events were from the 1970s, another three from the 1980s, four from the 1990s, and 12 in 2000 and beyond. This temporal distribution is skewed towards more recent occurrences, as expected, both due to the magnitude of the WTC (counted as four events) and Pentagon (one event) disasters of 9-11 and the news media searches.
The collapse distribution by building story height was as follows:
4-8 stories: 13
9-20: 3
21 or more: 6
Almost 60 percent of the cases are in the 4-8 stories range, with the remainder affecting much taller buildings. Six collapses occurred in buildings over 20 stories, and three of these were the WTC steel-framed buildings (1, 2, and 7).
At least four of these fire collapses had occurred during construction or renovations of some kind, when the usual expected architectural, structural, and fire protection functions were still incomplete or temporarily disrupted, and/or potential new fire sources were introduced, such as electrical and gas line repairs, welding, and the presence of other flammable supplies and/or equipment. Partial collapses (14 events) were the most frequent occurrences, and the WTC disasters (listed as four separate events, with three full collapses) dominated the full collapse event total of eight cases. Office and residential were the primary types of occupancy in these 22 buildings, as would be expected in multistory construction, with the occupancy distribution being as follows:
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