Videos of the 5:28 p.m. collapse of 7 World Trade lend vivid support to the truss-failure theory. Roughly 30 seconds before the building goes down, a rooftop mechanical room starts to disappear, falling into the building's core. Then a second larger rooftop room sinks. The building then quickly collapses.
Both rooms were above sections of the building held up by the trusses. Other video evidence shows fire concentrated in the floors containing the trusses and the fuel tanks.
I remember getting a call from the, er, fire department commander, telling me that they were not sure they were gonna be able to contain the fire, and I said, 'We've had such terrible loss of life, maybe the smartest thing to do is pull it.' And they made that decision to pull and we watched the building collapse.
In the afternoon of September 11, Mr. Silverstein spoke to the Fire Department Commander on site at Seven World Trade Center. The Commander told Mr. Silverstein that there were several firefighters in the building working to contain the fires. Mr. Silverstein expressed his view that the most important thing was to protect the safety of those firefighters, including, if necessary, to have them withdraw from the building.