Post-9/11 building codesHow the Terrifying Evacuations from the Twin Towers on 9/11 Helped Make Today’s Skyscrapers Safer

By Erica Kuligowski

Published 12 September 2021

One legacy of the 9/11 tragedy and the harrowing experience of those who successfully escaped the Twin Towers – the disaster was the most significant high-rise evacuation in modern times —  is that today’s skyscrapers can be emptied much more safely and easily in an emergency.

The 2001 World Trade Center disaster was the most significant high-rise evacuation in modern times, and the harrowing experiences of the thousands of survivors who successfully escaped the Twin Towers have had a significant influence on building codes and standards. One legacy of the 9/11 tragedy is that today’s skyscrapers can be emptied much more safely and easily in an emergency.

The 110-storey Twin Towers, constructed from 1966 to 1973, both had open-plan floor designs, with stairs and elevators located in the buildings’ core. Each tower had three staircases which, barring a few twists and turns, ran all the way from the top of the building down to the mezzanine level just above the ground floor. One of the stairways had steps 142 centimeters wide, but the other two measured just 112cm, which would not be permitted by today’s skyscraper building codes.

As a result of the Twin Towers’ system of “sky lobbies”, which was innovative for its time, the number of available elevators varied depending on the floor. The system was not designed to be used in an emergency, and today, many towers above a certain height are required to be fitted with dedicated emergency elevators or an additional staircase.

When the planes hit on the morning of September 11 2001, the Twin Towers were at less than half their full occupancy, with about 9,000 people in each tower. Many people who worked there had not yet arrived, partly because of a New York mayoral election scheduled for that day.

At 8:46am, American Airlines flight 11 slammed into the north face of the North Tower, rendering all three staircases impassable for anyone above the 91st floor. Sixteen minutes later, and after one-third of its occupants had already evacuated, the South Tower was hit by United Airlines flight 175, leaving only one staircase available for evacuees above the 78th floor.

Besides the problems posed by fires and damage on floors, and debris inside the stairways, people in both towers also faced issues with communication. The North Tower’s public address system, which would have been used to make emergency announcements to the building’s occupants, was disabled by the crash.

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