How the Terrifying Evacuations from the Twin Towers on 9/11 Helped Make Today's Skyscrapers Safer

In the South Tower, three minutes before the impact, occupants were told via the public address system to stay in place and wait for further information. Two minutes later they were told they could evacuate if they wanted. This may have meant more people from higher floors were waiting at the sky lobby on floor 78 when the plane crashed into that floor.

In both towers, people had only limited information on which to base their decisions. For those closest to the impacts, the seriousness of the situation and the need to evacuate was clear. But for those further away, who may have witnessed only the lights flicker, the uncertainty was palpable. Many people delayed their evacuation to seek out extra information, whether by speaking with colleagues, making phone calls, sending emails or searching online for news updates.

Many lives were saved by the brave leadership of people who took control of the situation, urging others to evacuate and helping those who needed assistance. My PhD research revealed these were typically people who were used to taking charge: high-level managers, fire wardens and people with military experience.

Hazardous Exit
Evacuees faced a dangerous and claustrophobic journey down to ground level. A subsequent US government investigation found 70% of evacuees encountered crowding on the stairs. Some people recalled having to leave the stairwell either because of overcrowding, being told to do so by fire or building officials, or because they needed a rest. Other problems included poor lighting, not knowing which direction to go, and finding the route unavoidably blocked by people with permanent or temporary disabilities.

While people are typically told not to use elevators in an emergency, 16% of those who escaped the South Tower used the elevators to evacuate during the 16 minutes between the two impacts. Simulations of a hypothetical 9/11 in which elevators were unavailable showed that occupants’ use of elevators saved 3,000 lives in the South Tower.

Not everyone was so lucky. The US National Institute of Standards and Technology (NIST) investigation (on which I was an author) estimated that between 2,146 and 2,163 people were killed in the towers, and that more people died in the North Tower, which was struck first. Most of those who died on 9/11 were on or above the floors hit by the planes.

Roughly 99% of people on floors below the impacts managed to evacuate successfully. For those who didn’t, the factors linked to their deaths included delaying their evacuation, performing emergency response duties, or being unable to leave their particular floor because of damage or debris. Had the buildings been fully occupied, the consequences would undoubtedly have been even worse.

Building Better
The stories of those who experienced the terrifying evacuations have helped to shape important and life-saving changes in high-rise buildings. The NIST report made several recommendations that were eventually implemented in a range of building codes and standards around the world, notably the International Building Code.

Emergency stairs in skyscrapers must now be at least 137cm wide, and feature glow-in-the-dark markings on the stair treads that are visible even if the power fails.

What’s more, while elevator use is not typically encouraged during building fires, the International Building Code now requires a new “occupant-safe” elevator system or an additional staircase in buildings over 128 meters tall. These new elevator systems are designed to be safely used during fires, offering a vital escape route for people unable to use stairs.

The tragic events of 9/11 changed the world in all sorts of ways. But hopefully, when it comes to the design of today’s skyscrapers, it has changed things for the better.

Erica Kuligowski is Vice-Chancellor’s Senior Research Fellow, RMIT University. This article is published courtesy of The Conversation.