Inside the Towers on 9/11: My Story of Investigating the WTC Evacuation

Credit: N. Hanacek/NIST

Jason Averill, Chief, Materials and Structural Systems Division, National Institute of Standards and Technology (NIST)

The kickoff meeting

On Nov. 1, 2002, in a small conference room on the Gaithersburg, Maryland, campus of the National Institute of Standards and Technology (NIST), the trio of outside experts ( Dennis Mileti, Guylene Proulx and Norman Groner) hired to work on evacuation and emergency communication project of the World Trade Center Investigation met for the first time with the NIST investigation team. As we were ready to start the day, Dennis Mileti preempted the introductions with a statement that, in retrospect, became a transformative notion guiding the work of the following years: “I would just like to say before we begin that there has never, in the history of evacuation and human behavior, been a study of this importance and with this level of funding. The work we do here will be the gold standard for evacuation and human behavior research for generations that follow and I’m privileged and humbled to be a part of this work.” My initial reaction, as a 28-year-old NIST engineer with one graduate class in evacuation as part of my fire protection engineering degree, was “OK. No pressure.” My second thought was, “How did I get here?” The answer to the latter question requires a little personal history and a circuitous series of circumstances that led to November 2002.

My personal background

On Sept. 8, 1994, US Air Flight 427 crashed into the rolling hills of Hopewell Township, Pennsylvania, on approach to the Pittsburgh airport, killing all 132 passengers aboard, including my father, Daniel Averill. As a junior in college, the event was life-altering in a myriad of ways that I could have scarcely understood. In addition to the challenges of suddenly losing a parent, there are two dimensions of my post-crash experience that are relevant to my involvement in the WTC investigation: engaging with support groups for families of aircraft accidents and the crash investigation by the National Transportation Safety Board (NTSB).

The Flight 427 Air Disaster Support League formed in the wake of the plane crash as a mechanism for families to heal through shared experience and my family became involved. Shortly thereafter, the Flight 427 families joined with other family groups to form the National Air Disaster Alliance (NADA), an umbrella organization dedicated to informing and educating the flying public on critical issues and advocating for reform. The notion of advocacy for survivors is powerful — it helps to believe that the tragic loss of a loved one can result in some positive change in the world, however big or small. Based upon a pattern of experiences, the NADA advocated to Congress for the provision of basic resources for families following air disasters (e.g., designated points of contact, training for those conducting notification), culminating in the Air Disaster Family Assistance Act. Further, President Clinton established the White House Commission on Aviation Safety and Security in 1996 and, through the NADA, I had an opportunity to testify before the Commission on Nov. 20, 1996, at L’Enfant Plaza in Washington, D.C., about my experience as a family member. The timing and location was fortunate as I was also exploring an opportunity to become an intern in the NIST Fire Protection Engineering Division. It was a unique conversation starter with my prospective group leader to say that I had just come from having breakfast with then-Vice President Al Gore and testifying before a White House Commission. Through this advocacy experience, I learned a lot about how the federal government works and the power of citizens to bring about positive change.

I also learned a lot about communication from the NTSB. The NTSB provided regular written and verbal communications to families regarding the progress of the technical investigation into the underlying cause of the Flight 427 crash. Specifically, the NTSB did not communicate an exact timeline for the investigation, instead declaring that they would investigate until they figured it out. Indeed, in March 1999, the NTSB issued the final report stating that “the rudder surface most likely deflected in a direction opposite to that commanded by the pilots as a result of a jam of the main rudder power control unit servo valve secondary slide to the servo valve housing offset from its neutral position and overtravel of the primary slide.” This conclusion was informed by laboratory experiments that demonstrated the critical failure mode in less than 1% of the experiments and left no evidence afterward — truly a remarkable achievement of engineering forensics. The investigation was the longest in the history of the NTSB and also solved the mystery of at least two other Boeing 737 crashes. Following the final report, NTSB Chair John Hall met personally with the families to explain the report and answer questions. Through this experience, I learned about the powerful sense of closure that a thorough technical investigation can provide to family members and the importance of taking the time and resources to get it right — indeed, following the Flight 427 report, no Boeing 737 has experienced a similar rudder reversal.

How my background could be useful to the investigation

Therefore, when Sept. 11, 2001, occurred, I felt a profound empathy for the many families experiencing a large-scale and sudden loss. In fact, the event had a personal dimension as my wife had stopped working at the Pentagon shortly before 9/11 due to the birth of our first child (Daniel), and we lost a close friend, Patty Mickley, at the Pentagon. In the ensuing weeks and months, it became clear that NIST would be conducting a technical investigation of the World Trade Center. I was moved to write a letter to the lead investigator, Shyam Sunder, who at the time was the chief of the Structures Division and a person whom I had never met. In my letter, I shared some of my personal experiences and argued for NIST to consider appointing a family liaison to act as conduit to the families to ensure that they would be prioritized for communications and have a mechanism to provide input to NIST. After some discussion, I was initially selected to serve as the WTC Family Liaison and lead the project documenting the fire protection systems in the towers. Then, two things happened at roughly the same time: we visited NTSB and my boss took a job in academia.

The visit to NTSB was helpful in many ways — they are experts at forensic engineering investigations and the National Construction Safety Team (NCST) authorities were written by Congress to mirror the NTSB authorities; in addition, they recommended that the family liaison not be a person that was also going to be involved in the technical investigation. I would have to choose between conducting technical work and working with families. At the same time, my supervisor left NIST — giving me the opportunity to be the project leader for the building evacuation project. The evacuation project would combine technical work with the opportunity to work with survivors and family members.

That is the long story of how I became the project leader for the evacuation project and Mat Heyman, then-NIST chief of staff, was installed as the family liaison. In retrospect, this worked well overall, as Mat was an outstanding intermediary to the families, eventually working principally with the leadership of an advocacy group that had (mostly) coalesced the families called the Skyscraper Safety Campaign.

Determining what happened inside the towers

As predicted by Dennis Mileti, the NIST investigation of the evacuation of WTC 1, 2 and 7 was one of the most comprehensive and rigorous technical studies of building evacuation ever. Along with colleagues Erica Kuligowski, Rick Peacock and Paul Reneke (and the trio of experts mentioned previously), we quickly gathered any existing information, including a database of over 700 evacuation accounts in the media, design documents for the building egress systems (stairwells, elevators, alarm and public address systems) and documented sitewide and tenant evacuation protocols (such as floor wardens, evacuation drills and prior evacuation events). We put out a public call for photos or videos from inside the building on September 11 (few of which existed) and importantly, how to participate in NIST interviews. We listened to every 911 emergency call from lower Manhattan that fateful morning, including many from inside the towers, both above and below the floors of impact. We listened to fire, police, and Port Authority radio records.

As a note, the NCST Act authority was a critical tool for conducting the investigation — for the evacuation project, we were able to obtain access to critical evidence such as the 911 calls and the “badge list” — the list of all individuals with badge access to the building, which also included the employer and building floor to which they were assigned. Further, the imprimatur of being the “official federal investigation” lent a credibility and objectivity to our efforts that was crucial for convincing some reluctant respondents to provide evidence or personal accounts. In fact, several of our interviews were conducted jointly with the 9/11 Commission in an effort to minimize the trauma for select interviewees having to recount their experience on September 11.

With the assistance of a team of trained contractors, we conducted three types of interviews with over 1,200 people, including: more than 800 telephone interviews using a uniform set of questions of randomly sampled interviewees from the badge list; more than 200 open-ended face-to-face interviews to allow novel or unexpected information to emerge; and six focus groups of people with shared experiences (such as people with mobility disabilities).

With this rich and diverse set of data, the project team wove a narrative of how the building evacuation commenced, interspersing data and facts with anonymized quotations that convey the perspectives of evacuees throughout the 102 minutes between the first aircraft impact and the collapse of the second tower. Key observations emerged that formed a strong basis for recommendations for changes to building codes, standards, and practices that can make other buildings safer and help ensure that outcomes like 9/11 won’t happen again in the future. For example:

  • 99% of the people who were below the floors of aircraft impact at the time their building was attacked were able to successfully evacuate. However, as the building was only partially full, egress modeling demonstrated that the stairwells would not have been adequate to fully evacuate all occupants if the building had been full.
  • In the 16 minutes between WTC 1 being attacked and WTC 2 being attacked, 40% of the building occupants evacuated WTC 2. This was attributable to the decision by WTC 2 occupants to immediately initiate their own evacuation and widespread use of the still-functioning elevator system in WTC 2.

Making a difference

Publishing a rigorous technical account of the events inside WTC 1, WTC 2 and WTC 7 hopefully provided some sense of closure to some families who wanted to know more about how their loved one perished on Sept. 11, 2001. However, the findings and recommendations from our nearly 450 pages of technical reports required active follow-through with standards and building code developing organizations to ensure that the lessons were fully acted upon. The code changes, such as requirements for photoluminescent markings in stairwells that can illuminate the path in the event of power loss and requirements to increase stairwell width from 1.2 meters (44 inches ) to 1.5 m (54 in), required a specific code change proposal and testimony from NIST and other like-minded advocates about how the findings from World Trade Center evacuation reports supported the proposed changes to convince hearing attendees to vote for adoption.

Other changes required upending one of the most effective public education campaigns in history — after all, everyone knows that you don’t use the elevator in the event of a fire. However, for ultra-tall buildings (generally considered to be buildings more than 40 stories), the efficacy of elevators is so apparent that it does not make sense to try and evacuate buildings that tall using only stairwells. In particular, when you consider that the Americans with Disabilities Act of 1990 mandates building access for people with disabilities (generally elevators) but does not mandate evacuation access during a fire when the elevators are taken out of service, elevators can provide more rapid and equal evacuation opportunity for tall buildings.

A consortium of interested parties, including NIST, firefighters, civil and mechanical engineering associations, elevator companies, and academics established a working group to develop code requirements that would enable the safe use of elevators by occupants during a fire and the fire service when trying to fight a fire (imagine hauling 45 kilograms (100 pounds) of gear up 80 flights of stairs before starting to fight the fire and rescue civilians). The working group met for one week at a time in the same Boston hotel every three months for five years. Using an ISO standard method to conduct a formal hazard analysis that finally required 600 pages, the working group proposed changes to the Elevator Code (ASEM A17.1) and to the International Building Code (Chapter 30) that require the new elevator systems in buildings over 122 m (400 feet) or one additional stairwell beyond the minimum number otherwise required. Analysis by the NIST Applied Economics Office demonstrated that the elevator systems have far superior economic benefit as the additional stairwell consumes a significant amount of leasable square footage and practice has shown developers’ preference for elevators over additional stairs. In addition, persons with mobility disabilities now have equality of egress opportunity.

In summary, my experience with the World Trade Center Investigation has had a significant impact on my life personally and professionally. The opportunity to connect my personal life experiences to such a landmark event ignited a sense of purpose in my work that is motivating and rewarding. I am proud of the technical work that the evacuation team performed and just as proud that we achieved more than a dozen significant evacuation-related changes to building codes, standards, and practices making tall buildings safer for people to live and work in.

This post originally appeared on Taking Measure, the official blog of the National Institute of Standards and Technology (NIST) on September 3, 2021.

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About the Author

Jason Averill is the chief of the Materials and Structural Systems Division. Mr. Averill started at NIST in the Fire Protection Engineering Division in 1997 and has devoted his technical career to making buildings safer for the public and first responders, first as a research fire protection engineer and currently overseeing technical work involving community resilience, earthquake and wind engineering, and material science.



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