December 14, 2007: NIST Fact Sheet Responds to Questions about Its WTC Investigation

The National Institute of Standards and Technology (NIST) publishes a fact sheet responding to 14 “frequently asked questions” about its investigation into the collapse of the Twin Towers on September 11. Some of the key questions and answers are as follows:
Regarding the question, “Why was the collapse of WTC 1 and 2 not arrested by the intact structure below the floors where columns first began to buckle?” NIST replies, “The vertical capacity of the connections supporting an intact floor below the level of collapse was adequate to carry the load of 11 additional floors if the load was applied gradually and 6 additional floors if the load was applied suddenly (as was the case).” As the number of floors above the points where the collapses initiated exceeded six (12 in the case of the North Tower, 29 for the South), NIST says, “[T]he floors below the level of collapse initiation were unable to resist the suddenly applied gravitational load from the upper floors of the buildings.”
In answer to the question of “Why was physical evidence not collected immediately following the collapse of the WTC towers,” NIST says, “In the initial days and weeks following the WTC disaster, the emphasis was on rescue and later on recovery, necessitating the removal of steel and disturbing the collapse site.” It adds, “NIST did not receive the legal authority to collect and preserve physical evidence from a disaster/failure site until the National Construction Safety Team Act became law in October 2002.” The decision to rapidly scrap the remaining steel from the WTC was made shortly after 9/11 (see Shortly After September 11, 2001), but the destruction of this steel was strongly protested by some within the engineering and firefighting communities (see December 25, 2001 and January 4, 2002).
In response to a question about why it did not use its subpoena authority during its investigation, NIST states that its “experience during the investigation was that it was able to obtain all essential documentary and visual evidence without the need to invoke subpoena authority.”
In answer to the question, “Why didn’t NIST fully model the collapse initiation and propagation of WTC towers?” NIST says, “Once the collapse had begun, the propagation of the collapse was readily explained without the same complexity of modeling” as was used to determine the sequence of events leading up to the collapse initiation.
During its investigation, NIST had selected several variables for its computer simulations, and then experimented with different possible values (see (October 2002-October 2005)). But it has been asked: “Why didn’t NIST consider the ‘base’ and ‘less severe’ cases throughout its analysis of the WTC towers? What was the technical basis for selecting only the ‘more severe’ case for its analyses?” Its answer is that, “Of the three [possible values], the more severe case resulted in the closest agreement with the visual and physical evidence.” [National Institute of Standards and Technology, 12/14/2007]
NIST published its final report on the Twin Towers collapse in October 2005 (see October 26, 2005). It released an earlier fact sheet answering previous “frequently asked questions” in August 2006 (see August 30, 2006). [National Institute of Standards and Technology, 8/30/2006]