On the other hand, World Trade Center Building 7 (WTC 7) collapsed even though it was not hit by aircraft. The 47-story office building caught fire after debris from WTC 1 fell on it, and the flames spread uncontrolled because its sprinklers also did not work—city water lines were damaged in the destruction of the Twin Towers. In the 2008 report on the breakdown of WTC 7, NIST investigators concluded the fire then caused steel floor beams and girders to expand, resulting in unexpected structural weakness and triggering a progressive collapse, the first known instance of a tall building brought down primarily by uncontrolled fires.
In light of these disasters, NIST issued 31 recommendations to improve the safety of high-rises and the emergency responses in the face of major threats. Critics did emerge against these recommendations, including from another federal agency, the General Services Administration. Concerns included the costs of these changes, "and when that happens, that's because they're not really convinced of the benefits, and I think that's because there was a lack of consensus over the results of the investigation," notes Guy Nordenson, a Princeton professor of architecture and structural engineering who runs a structural engineering firm in New York and was not involved in the NIST investigation.
Earlier NIST recommendations were received more easily. For instance, in the late 20th century, when NIST undertook a large investigation of building designs and their readiness for earthquakes, it had broad involvement from the engineering community and thus its recommendations were widely accepted by the field. "The problem many have with the World Trade Center investigation is that it wasn't as open and not adequately peer reviewed, due in part to the veil of security concerns, so lots of people can disagree with the conclusions," Nordenson says. For instance, Nordenson himself is part of litigation suggesting the collapse of WTC 7 was not inevitable, but was due to design flaws in both the fire protection and some aspects of the structure.
Sunder defended NIST's investigation, noting that the federal agency endeavored to make it as open and inclusive as possible, with numerous opportunities for the public and engineering community to review and provide input, such as public meetings, comment periods and advisory committee meetings that were open to the public. He also stood by its conclusions regarding WTC 7, saying "NIST has not seen any data or analyses from other researchers that would lead NIST to reevaluate its findings."
As to what happened with NIST's recommendations, "23 changes to the 2009 editions of the International Codes and another 17 changes to the 2012 editions, responsive to the recommendations, have been adopted," Sunder says. These building and safety codes from the International Code Council "are typically adopted by state and local authorities."
For instance, buildings taller than 420 feet are now required to include an extra exit stairwell or a specially designed elevator that occupants can use for evacuations. Also, stairwells in buildings more than 75 feet high must now have glow-in-the-dark markings that show the exit path even when lighting is out or dim. In addition, spray-applied fire-resistive materials must perform four times more effectively than current requirements in buildings 75 to 420 feet tall, and more than seven times better in buildings taller than 420 feet. "The code changes have broad implications for building safety," Sunder says.
So far, New York City has already made significant changes in response to NIST recommendations, Sunder notes, as have many new projects in the United States, such as One World Trade Center, the lead building of the new World Trade Center complex. "The speed, magnitude and scope of changes in response to the recommendations of the World Trade Center investigation have been truly remarkable," he says.