Monday, January 22, 2007

NIST: A Boeing 707 travelling at 600 mph 'would result only in local damage which would not cause collapse'

"The buildings have been investigated and found to be safe in an assumed collision with a large jet airliner (Boeing 707 - DC 8) traveling at 600 miles per hour. Analysis indicates that such collision would result only in local damage which would not cause collapse or substantial damage to the building and would not endanger the lives and safety of occupants not in the immediate area of impact."

That's from a February 3, 1964 memo released by the National Institute of Standards and Techonology (NIST), the U.S. government agency responsible for analyzing the collapse of 1 and 2 World Trade Center, and NIST's recent analysis appears to support it.

The memo says: "The structural analysis carried out by the firm of Worthington, Skilling, Helle & Jackson is the most complete and detailed of any ever made for any building structure."

The February 3, 1964 memo is included as Appendix A to "Baseline Structural Performance and Aircraft Impact Damage Analysis of the World Trade Center Towers," NISTNCSTAR1-2, April 26, 2006.

Executive Summary, Table E-8 of the NIST report estimates aircraft impact speeds at 443 mph plus or minus 30 for AA 11 (WTC 1), and 542 mph plus or minus 24 for UAL 175 (WTC 2).

Executive Summary, Finding 18 states that "the tower still had reserve capacity after losing a number of columns and floor segments due to aircraft impact."

"NIST concluded that the WTC towers collapsed because: (1) the impact of the planes severed and damaged support columns, dislodged fireproofing insulation coating the steel floor trusses and steel columns, and widely dispersed jet fuel over multiple floors; and (2) the subsequent unusually large jet-fuel ignited multi-floor fires (which reached temperatures as high as 1,000 degrees Celsius) significantly weakened the floors and columns with dislodged fireproofing to the point where floors sagged and pulled inward on the perimeter columns. This led to the inward bowing of the perimeter columns and failure of the south face of WTC 1 and the east face of WTC 2, initiating the collapse of each of the towers."

NIST expects to release a draft report on the collapse of WTC 7 by "early 2007."