Reconstruction of the fires in the World Trade Center towers

Abstract

Certain commercial entities, equipment, products, or materials are identified in this document in order to describe a procedure or concept adequately or to trace the history of the procedures and practices used. Such identification is not intended to imply recommendation, endorsement, or implication that the entities, products, materials, or equipment are necessarily the best available for the purpose. Nor does such identification imply a finding of fault or negligence by the National Institute of .Standards and Technology. Disclaimer No. 2 The policy of NIST is to use the International System of Units (metric units) in all publications. In this document, however, units are presented in metric units or the inch-pound system, whichever is prevalent in the discipline. Disclaimer No. 3 Pursuant to section 7 of the National Construction Safety Team Act, the NIST Director has determined that certain evidence received by NIST in the course of this Investigation is "voluntarily provided safety-related information" that is "not directly related to the building failure being investigated" and that "disclosure of that information would inhibit the voluntary provision of that type of information" (15 USC 7306c). In addition, a substantial portion of the evidence collected by NIST in the course of the Investigation has been provided to NIST under nondisclosure agreements. Disclaimer No. 4 NIST takes no position as to whether the design or construction of a WTC building was compliant with any code since, due to the destruction of the WTC buildings, NIST could not verify the actual (or as-built) construction, the properties and condition of the materials used, or changes to the original construction made over the life of the buildings. In addition, NIST could not verify the interpretations of codes used by applicable authorities in determining compliance when implementing building codes. Where an Investigation report states whether a system was designed or installed as required by a code provision, NIST has documentary or anecdotal evidence indicating whether the requirement was met, or NIST has independently conducted tests or analyses indicating whether the requirement was met. Use in Legal Proceedings No part of any report resulting from a NIST investigation into a structural failure or from an investigation under the National Construction Safety Team Act may be used in any suit or action for damages arising out of any matter mentioned in such report (15 USC 281a; as amended by P.L. 107-231).

The influence of travelling fires on a concrete frame

“…Although it may be possible to replicate these conditions in a furnace, a recent experimental review of post-flashover tests [15] has clearly demonstrated that temperature conditions are non-uniform in most compartments. Moreover, the major fires at the Windsor Tower [17], World Trade Center [18,19] and TU Delft [20] have shown that fires tend to travel around large compartments rather than burn uniformly. Tests have also shown the there is a high degree of temperature variation even within small compartments [21][22][23].…”

Experimental review of the homogeneous temperature assumption in post-flashover compartment fires

“…Due to the travelling nature of the fires, it is likely that temperature distributions during these events were highly non-uniform. While no data exist to validate this, extensive numerical simulations conducted for the World Trade Center investigations by NIST clearly show temperature variations within single compartments of several hundred degrees Celsius [18,19].…”

“…Since the scale of most enclosures in real buildings is significantly larger than the scale in the few experimental tests available, it is likely that even higher degrees of non-uniformity are to be expected in real fires. Real, large fires that have led to structural failure, such as those in the World Trade Center towers 1, 2 [18] and 7 [19] in New York in September 2001, the Windsor Tower in Madrid, Spain in February 2005 [20] and the Faculty of Architecture at TU Delft in the Netherlands in May 2008 [21] were all observed to travel across floor plates. Due to the travelling nature of the fires, it is likely that temperature distributions during these events were highly non-uniform.…”

Travelling fires for structural design-Part II: Design methodology

“…Accidental fires that have led to structural failure [6,7,8,9] have been observed to travel across floor plates, and vertically between floors, rather than burn uniformly. Travelling fires have also been observed experimentally in compartments with non-uniform ventilation [10,11,12].…”

“…These two assumptions, which have never been confirmed experimentally, led to limitations in the use of the traditional methods in large compartments. Details of the limitations and their implications are given in Part I of this paper and in the literature [3,4,5].Accidental fires that have led to structural failure [6,7,8,9] have been observed to travel across floor plates, and vertically between floors, rather than burn uniformly. Travelling fires have also been observed experimentally in compartments with non-uniform ventilation [10,11,12].…”