Miracles of 9/11: Firefighters
"Remember this area here was really the, the sanctuary particularly right about in the middle of it. That's where Stairway B was. And so what happened is the plane hit here on the 94th floor. There were about ten floors above it. Once the steel gets above 600 degrees or so it loses most of its structural strength. As the floors collapsed on one another and pancaked on top of one another on the way down, by the time it got down to the lower floors you had the weight of 75 floors of building pressing on this area but fortunately the debris field by then had spread wider and so it scattered outward," says Ross.
He also finds that due to the way the floors pancaked as the building collapsed, the stairway could remain standing as the floors fell around it. Ross identifies a survival zone from approximately floor 6 to floor twenty of Stairway B. This is the only such zone in the entire building.