NIST Versus Rosie: No Contest

The National Institute of Standards and Technology (NIST) has released its long-awaited analysis of what happened to World Trade Center 7 on 9/11/2001. The troofers (including Rosie "Unemployed" O'Donnell) have long theorized that fire could not have brought the building down. The NIST begs to differ. Fire did, indeed, bring the building down. That opens up some rel concerns since many tall buildings may be inadequately designed to handle fires without suffering structural failure.

Today's report confirms that a fire was, indeed, the cause. "This is the first time that we are aware of, that a building taller than about 15 stories has collapsed primarily due to fires," Sunder told reporters at the press conference. "What we found was that uncontrolled building fires—similar to fires experienced in other tall buildings—caused an extraordinary event, the collapse of WTC7." The unprecedented nature of the event means that understanding the precise mechanism of the collapse is important not just to answer conspiracy theorists' questions, but to improve safety standards in the engineering of large buildings.

The final report describes how debris from the collapse of WTC 1 ignited fires on at least 10 floors of WTC 7 at the western half of the south face. Fires on Floors 7 through 9 and 11 through 13 burned out of control, because the water supply to the automatic sprinkler system had failed. The primary and backup water supply to the sprinkler systems for the lower floors relied on the city's water supply. Those water lines were damaged by the collapse of WTC 1 and 2. These uncontrolled fires in WTC 7 eventually spread to the northeast part of the building, where the collapse began.

After 7 hours of uncontrolled fires, a steel girder on Floor 13 lost its connection to one of the 81 columns supporting the building. Floor 13 collapsed, beginning a cascade of floor failures to Floor 5. Column 79, no longer supported by a girder, buckled, triggering a rapid succession of structural failures that moved from east to west. All 23 central columns, followed by the exterior columns, failed in what's known as a "progressive collapse"—that is, local damage that spreads from one structural element to another, eventually resulting in the collapse of the entire structure.

As the report points out, joints in these buildings are designed to resist the downward pull of gravity, not the lateral stress of a structural member expanding rapidly in a hot fire. Popular Mechanics continues to do yeoman's work slapping down the troofers with hard facts.

Found via Neptunus Lex.