"5:21:03 p.m. Approximately 30 seconds later, Figure 5-21 shows the east mechanical penthouse disappearing into the building. It takes a few seconds for the east penthouse to "disappear" completely." - FEMA (05/02)

~5:21:08 p.m. Approximately 5 seconds later, the west mechanical penthouse disappears (Figure 5-22) or sinks into WTC 7.

~5:21:09 p.m. Approximately 1 or 2 seconds after the west penthouse sinks into WTC 7, the whole building starts to collapse. A north-south "kink" or fault line develops along the eastern side as the building begins to come down at what appears to be the location of the collapse initiation (see Figures 5-23 and 5-24).

~5:21:10 p.m. WTC 7 collapses completely after burning for approximately 7 hours (Figure 5-25). The collapse appeared to initiate at the lower floors, allowing the upper portion of the structure to fall." - FEMA (05/02)

"The debris generated by the collapse of WTC 7 spread mainly westward toward the Verizon building, and to the south... The average debris field radius was approximately 70 feet.
The collapse of WTC 7 had a small debris field as the facade was pulled downward, suggesting an internal failure and
implosion." - FEMA (05/02)


"...when you need to bring down a massive structure, say a...skyscraper, you have to haul out the big guns. Explosive demolition is the preferred method for safely and efficiently demolishing larger structures. When a building is surrounded by other buildings, it may be necessary to "implode" the building, that is, make it collapse down into its footprint." - HowStuffWorks.com

America Rebuilds: A Year at Ground Zero -PBS (09/10/02)

Narrator: "World Trade Center 7 had always been considered the starting point for rebuilding.

Larry Silverstein, WTC Leaseholder: "I remember getting a call from the, uh, fire department commander, telling me that they were not sure they were gonna be able to contain the fire, and I said, 'You know we've had such terrible loss of life, maybe the smartest thing to do is, is pull it.' Uh, and they made that decision to pull and then we watched the building collapse." - Audio


(Unidentified construction worker): "Hello? Oh, we're getting ready to pull building six."

Luis Mendes, NYC Dept of Design and Construction: "We had to be very careful how we
demolished building six. We were worried about the building six coming down and then damaging the slurry walls, so we wanted that particular building to fall within a certain area." - Audio