An expert on the Sept. 11 collapse of the World Trade Center explained Monday how researchers discovered that the fires from the explosion caused the twin towers to collapse.

W. Gene Corley, who headed the committee of postmortem studies for the American Society of Civil Engineers, detailed for Northwestern engineering professors and students both past misinterpretations and truths about why the towers collapsed.

Corley maintained that the buildings did not collapse because the fires were hotter or lasted longer than the building could stand. He illustrated his point by showing a photograph, taken of the hole in one of the towers shortly after the crash, in which a person standing inside the building did not appear affected by the heat.

“There is a person standing there who is not bothered by the heat and from that we determined that this is a normal office fire,” Corley said.

He also presented the audience with a photograph of a large fireball enveloping a portion of each of the towers, arguing the initial fire burned out within three to nine minutes and exhausted all the fuel from the plane.

According to Corley, the initial impact weakened the buildings so much that any extra disturbance, including the fires that followed, would have caused a collapse.

“A strong wind would’ve done the same thing,” Corley said. “It is our position that if there had been no fire, the buildings would have stood indefinitely until some other major occurrence.”

Although the fires did not burn long, they burned thoroughly, he said. One of the major reasons the fires burned the buildings as completely as they did was the fact that the sprinklers failed to work, he said.

When the planes hit the towers, they cut through the water supply that would otherwise have helped calm the fires, Corley said.

Corley went on to discuss the fire-proofing of the internal columns done during the construction of the buildings in the 1960s, which also contributed to the building’s collapse. Much of the World Trade Center’s fire-proofing was not secured strongly enough to withstand the impact of the planes hitting the buildings.

Civil engineering Prof. Ray Krizek pointed out the preparation that was done on the part of the World Trade Center’s structural engineers.

“They did design for an (airplane) hitting it,” Krizek said.

Structurally, the buildings should have been able to withstand the impact, Corley said. The fire-proofing, an aspect that the architect designs, was the ultimate problem.

“You’ve never heard anyone say the architect screwed up,” Corley said. “They say, ‘What did the structural engineers do wrong?'”

Ahmad Hadavi, a civil engineering professor and associate director of the masters of project management program, attributed this misunderstanding to the public’s image of an architect as just a designer.

“People think of an architect as the artist who thinks of what to do with the space, not (as a person) who thinks of structural considerations,” Hadavi said.