But for those further away, who may have witnessed only the lights flicker, the uncertainty was palpable. For those closest to the impacts, the seriousness of the situation and the need to evacuate was clear. In both towers, people had only limited information on which to base their decisions. 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.ĩ/11 conspiracy theories debunked: 20 years later, engineering experts explain how the twin towers collapsed Two minutes later they were told they could evacuate if they wanted. 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. 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. 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.īesides the problems posed by fires and damage on floors, and debris inside the stairways, people in both towers also faced issues with communication. Many people who worked there had not yet arrived, partly because of a New York mayoral election scheduled for that day.Īt 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. 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. 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. One of the stairways had steps 142 centimetres wide, but the other two measured just 112cm, which would not be permitted by today’s skyscraper building codes.Īs 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. 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. 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. The twin towers’ elevator layouts meant getting to ground level was more complicated on some floors than on others. RMIT University provides funding as a strategic partner of The Conversation AU. Finally, Erica gratefully acknowledges the UK WTC project HEED, funded by the UK EPSRC (grant EP/D507790/1) for providing access to the HEED database, which was used in her PhD thesis. While at NIST, Erica worked on NIST's Technical Investigation of the 2001 WTC Disaster as a team member of Project 7: Occupant Behavior, Egress, and Emergency Communications. Also, from 2002 to 2020, Erica worked as a research engineer and social scientist in the Engineering Laboratory of the National Institute of Standards and Technology. She is affiliated with the Society of Fire Protection Engineers (SFPE) as a Section Editor for their Handbook of Fire Protection Engineering (Human Behaviour Section) and as a member of the Board of Governors for the SFPE Foundation. Vice-Chancellor's Senior Research Fellow, RMIT UniversityĮrica Kuligowski currently receives funding from the National Institute of Standards and Technology's (NIST) Measurement Science and Engineering Grants Program (as a subcontractor).
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