By Kathianne Boniello
For all the fires Vincent Dunn had seen and fought throughout his more than 40 years with the city Fire Department, the published author and well-regarded safety consultant was still surprised by the speed of the Sept. 11 collapse of the World Trade Center.
“I never believed a 110-story building would come down 11 floors per second,” the longtime Douglaston resident said during a Tuesday night presentation to the Douglaston Civic Association. “None of us ever believed these buildings would come down.”
On Sept. 11 terrorists hijacked two commercial airliners and slammed them into the Twin Towers of the World Trade Center, causing an explosion of jet fuel, a long-burning fire and the eventual toppling of the buildings. Some 3,000 people were killed, including 343 firefighters who rushed into the towers before they fell.
Dunn, a noted expert on fires in hi-rise buildings, wrote in a report released shortly after Sept. 11 that the Twin Towers’ unique design and construction should be considered as a contributing factor to the buildings’ collapse. He retired as a deputy fire chief.
“There’s never one single factor that makes a building collapse,” Dunn told the audience of about 50 gathered at Zion Episcopal Church. “Pilots call it a ‘cascading effect’ in a plane crash, where it’s one thing that goes wrong after another that causes a crash.”
At least three major factors played a role in the trade center’s collapse, Dunn said: the force of the 185-ton Boeing 767 airplanes hitting the buildings, fires created by 24,000 gallons of exploding jet fuel, and the towers’ construction.
The style of construction used in the construction of the 110-story tall Twin Towers was widely recognized as unique and included a number of engineering innovations.
As opposed to a traditional steel structure which uses large amounts of concrete and interior columns to support the weight of a building, the World Trade Center towers reversed the equation, Dunn said.
Engineers created an exterior wall of vertical tubes, often referred to as a girdle, to give the building its main supports with other heavier steel skeletons in the center of each building. Dunn said the effect created wide open, columnless spaces with little interior support.
Because builders in the early 1970s sought to make structures lighter and cheaper, Dunn said they moved away from heavier, more fire-resistant buildings.
“Fire resistance is directly related to the mass of a structure,” he said.
“When that plane struck the World Trade Center, it went through that outer wall — the collapse started right there — and skidded through the open floor space unimpeded by any columns,” Dunn said. “Those buildings were doomed.”
Unlike the trade center, the Empire State Building was constructed with much more concrete and far fewer structural weaknesses such as central air conditioning, said Dunn.
If the Empire State Building had been hit by the terrorist attack, Dunn said: “I believe that it would not have come down.”
Reach reporter Kathianne Boniello by e-mail at Timesledgr@aol.com or call 229-0300, Ext. 146.