World Trade Center, Collapse of The 18
World Trade Center, Collapse of The 18 : Investigations: (2) NIST Report: The outer shell of the South Tower (tower 2) of the WTC is still standing at right. The 22-story Marriott Hotel in the foreground was crushed when the adjacent tower collapsed. After the FEMA report had been published, and following pressure from technical experts, industry leaders and families of victims, the Commerce Department's National Institute of Standards and Technology conducted a three-year, $16 million investigation into the structural failure and progressive collapse of several WTC complex structures. The study included in-house technical expertise, along with assistance from several outside private institutions, including the Structural Engineering Institute of the American Society of Civil Engineers, Society of Fire Protection Engineers, National Fire Protection Association, American Institute of Steel Construction, Simpson Gumpertz & Heger Inc. , Council on Tall Buildings and Urban Habitat, and the Structural Engineers Association of New York. The scope of the NIST investigation was focused on identifying "the sequence of events" that triggered the collapse, and did not include detailed analysis of the collapse mechanism itself (after the point at which events made the collapse inevitable). In line with the concerns of most engineers, NIST focused on the airplane impacts and the spread and effects of the fires, modeling these using the software program Fire Dynamics Simulator
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