Two Chicagoans are part of that change.
Bill Baker, partner of Skidmore, Owings & Merrill, was part of a team called to Ground Zero to learn why the twin towers collapsed. His firm has designed six of the tallest buildings ever, including Chicago's Willis Tower.
"When we saw the building, saw the fires, we thought perhaps it was going to survive," Baker said. "What we were not thinking about at the time, which later turned out to be true, is that airplanes knocked off so much of the fireproofing."
Fire-proofing material is spayed on steel columns and beams during construction. When the impact of the planes knocked off that material, the steel was exposed to intense heat and eventually bent like taffy, unable to carry the floors above.
Civil engineer Gene Corley was also part of the team with Baker that examined the World Trade Center collapse.
"When I first saw what had happened, my thought was I'm surprised they didn't collapse immediately," Corley said.
The team's investigation led to several recommendations, including constructing wider stairwells, adding more exit stairways, a designated fire service elevator for emergency responders and people with mobility problems and the bonding for fire-proofing material on structural beams be seven times stronger in skyscrapers.
"I would very much like to see these adopted universally," Corley said. "I think they improve the safety of buildings and give people a better chance to get out of there if there's a fire or if there is some other unusual event."
The city of Chicago has not adopted these recommendations but officials say changes will be considered when it revises building codes.