Let me make a few clarifications on your article, "Research May Never Pinpoint Sequence of Events on 9/11," about the federal building and fire safety investigation of the World Trade Center disaster being conducted by the National Institute of Standards and Technology (ENR 1/19 p. 12).
First, NIST seeks to determine the most probable structural collapse sequence for each tower, from the several scenarios under consideration, using established statistical and probabilistic analysis methods. The methodology is described in Appendix 5, p. 93, of the May 2003 progress report that is available on the NIST World Trade Center Website, http://wtc.nist.gov. While we recognize that it is possible there may not be a unique collapse sequence, we are not far enough along in our analyses to make that determination at this time.