The Code War

The collapse of the Twin Towers taught us many things about skyscraper safety. Will we actually use the knowledge?



A building is a compromise — a bundle of risks safe enough to use, but dangerous enough to regulate.


How tall is too tall, how safe is safe enough? Before September 11, Americans thought little about such questions. And then the most extraordinary buildings in New York City burned and collapsed in front of a worldwide audience. Though the Twin Towers had long been scrutinized for their vulnerabilities (especially after the 1993 bombing), no one — not even their harshest critics — spent much time contemplating whether they would collapse as a result of catastrophic fires. Once people got past the simple explanation of the disaster — “the terrorists did it” — a  much more difficult truth emerged. We trust that our buildings are safe without knowing much about them.

The work of establishing American building codes and safety standards is hidden in plain sight, open to public view but rarely of interest. This is curious considering how critical building safety is to everyday life. Still, the fact remains that most Americans assume safety until events show the contrary. Public outrage after disasters from the Triangle Shirtwaist Factory Fire to Hurricane Katrina are constants throughout American history. But it is a rare case in which public action motivates government-funded research and moves the national conversation on building safety in a proactive way. Skyscraper safety since September 11 is one such case. But how far can the will to investigate and learn from disaster move away from the disaster itself? Is 10 years too far away?

The disaster experts investigating the collapse of the World Trade Center have found themselves in an uncomfortable position since September 11, trying to understand what went wrong, while at the same time explaining to impatient members of Congress and grieving families the ways that building and fire safety codes are created and tended in the United States. It is not a system designed for rapid response to a call for action. And, as much as the disaster experts may wish it to be otherwise, factors of cost matter.

Safety, innovation, and profitability all teeter on the wire of American risk-taking. The safest building is never the cheapest building. Developers, architects, and structural engineers are focused on construction, and safety resides within the bounds of probability — they trust in the community of experts to prescribe building codes, and they use them. The result is usually impressive and profitable, until it isn’t. Firefighters, fire protection engineers, and the people who live and work in skyscrapers usually err on the side of redundancy and protection: They want buildings that are reliable under even extreme conditions such as a plane crash or major fire. Finding consensus among these different parties is an ongoing process that leaves none of them fully satisfied, but results in the ever-changing landscape of the American skyscraper and the ever-changing codebook of skyscraper safety.

Families and Experts

A few months after September 11, Sally Regenhard attended a meeting of firefighters’ families in a Manhattan office building. Her son Christian, a probationary fireman, had been killed while responding to the World Trade Center attacks. His body remained missing. Walking across the lobby, she saw a gathering of reporters and learned from a security guard that Senator Hillary Clinton was in the building. The Senator would soon be coming downstairs to talk to the press. Regenhard’s letters and calls to Senator Clinton’s office, Senator Chuck Schumer’s office, Federal Emergency Management Agency (FEMA) headquarters — to any government official who might take an interest in investigating the deadliest, costliest building collapse in American history — had all gone unanswered. In those days, Regenhard always wore a business suit and always carried pictures of her son in his firefighter’s uniform, ready for any chance to make her case.

She waited.

When Senator Clinton arrived and began the press conference Regenhard waded into the crowd. She raised her hand at an opportune moment. Clinton acknowledged her, and Regenhard pulled out Christian’s picture and her petition.

“My name is Sally Regenhard, and this is a picture of my son.” Every head turned and the television lights went on. She owned the moment.

“Senator Clinton, will you support a federal investigation into the collapse of the World Trade Center?” she asked.

There was a pause.

“Yes, yes I will,” Clinton said.

The event was briefly noted in the papers, but for Regenhard and her grassroots organization, the Skyscraper Safety Campaign, it was the first win in an emotionally charged effort to force a public debate over why the World Trade Center collapsed — and what we should be doing to make high-rise buildings safer.

In the days and weeks after September 11 disaster, experts tried to understand the collapse of the Twin Towers. A “Building Performance Assessment Team” was rapidly assembled, coordinated by the American Society of Civil Engineers and FEMA. This was a common practice after major structural disasters such as the Oklahoma City and 1993 World Trade Center bombings. But this time the investigators quickly ran into frustrating difficulties. Without subpoena power, the experts’ requests for building plans, 911 call records, video, and photo data were blocked. Even gaining access to the site itself was a challenge. Meanwhile the wreckage — the steel that held the secrets to the fires and the collapse — was being hastily loaded onto trucks and shipped to New Jersey scrap yards for recycling, some of it already on its way to China. The grim search for bodies ruled the front page, as did the opening act of the Bush administration’s War on Terror. The idea that the World Trade Center had collapsed due to fire could not yet penetrate the public or governmental consciousness.

Meanwhile, Sally Regenhard, Monica Gabrielle (whose husband Richard had died in the collapse), and an expanding group of victims’ families were forming around shared impatience with their inability to get even basic answers about what had gone wrong in the Towers. Looking for any information they could use, they came across John Jay College fire protection engineering professor Glenn Corbett and Berkeley structural engineering professor Abolhassan Astaneh-Asl. The two disaster experts had received attention for their criticism of the disaster investigation’s lack of progress. The Skyscraper Safety Campaign was created on this common ground, harnessing the moral authority of families of the dead and advised by experts who were focused on the fire protection defects of the Towers. The effort saw some progress. Regenhard had her serendipitous lobby meeting with Clinton. Late in 2001, a timely New York Times story noted the failures of the technical investigation. New York’s congressional delegation jumped on it, with Clinton and Schumer calling for an investigation.

Two of New York’s House members, Democrat Anthony Weiner and Republican Sherwood Boehlert, took the lead. Members of the House Science Committee, Boehlert and Weiner convened two tense meetings in the spring of 2002. “The Building Performance Assessment Team is composed of an elite group of engineers and scientists,” Glenn Corbett noted in his testimony. Nevertheless, they had “allowed valuable evidence in the form of the towers’ structural steel to be destroyed.” Committee chairman Boehlert picked up on Corbett’s criticism. “We need to understand a lot more about the behavior of skyscrapers and about fire if we are going to prevent future tragedies,” he warned.

In the most widely reported episode from the hearings Representative Weiner asked a seemingly simple question. “Will the person who is in charge of the investigation raise their hand?” Two hands went up, and then a third. “I want to know who is in charge,” Weiner demanded. “Where does the buck stop . . . on this investigation?”  National Institute of Standards and Technology (NIST) director Arden L. Bement answered that it was, in fact, his investigation to run. Weiner wanted to know more about why examining the steel debris was critical. “You said that we have the capability to determine the impact of heat on structural failure in buildings. . . . Do you believe that if we had that information before September 11, some of the people that are sitting behind you would not have lost loved ones?” Weinter asked. This was the question that mattered most to the skyscraper safety advocates. Did the experts have the knowledge to prevent the worst from happening, and if so, could they have used it to anticipate the catastrophe, to prevent September 11 in New York from being more than two plane crashes into the Twin Towers?

“Perhaps. Yes,”  Bement replied.

This was a revealing admission. It acknowledged that simply knowing how to build more resilient structures did not — does not — guarantee that such knowledge will be used. When it comes to preventing American disasters, knowledge itself is often not the problem.

Surprising to many is the fact that the United States does not have a centralized process for implementing expert recommendations on fire protection and building safety. The country’s national fire protection and building safety system was created in the decades when American cities burned down in horrific conflagrations — a time when the federal government was not active in public safety, state and local government were unwilling to inhibit construction, and when insurance companies and average citizens were paying high prices for the fire dangers of the city. In this context, organizations such as the National Fire Protection Association (NFPA) and Underwriters Laboratories — initially founded by or closely associated with fire insurers — emerged as science-based clearinghouses for risk and disaster research. Building code groups grew similarly, merging in 1994 as the International Code Council (ICC), responsible for the widely used International Building Code. With input from the fire service, insurance companies, architects and engineers, industry and building trades, and government the experts developed what they call “consensus codes” — standards of safety and performance that are codified into law in most states and cities. The process is deliberative, slow, and decentralized, much like democracy itself.

After scolding the disaster experts for not yet having the answers, the House Science Committee moved to continue the investigation, pushing forward a 16 million dollar appropriation to support a long-term NIST study. Formerly known as the National Bureau of Standards, NIST is the only American national laboratory focused on structural and fire safety, maintaining a state-of-the art research complex in the suburbs of Washington, D.C. Congress also passed the National Construction Safety Team Act, a bill that granted subpoena powers to NIST, putting the organization clearly in control of building collapse investigations. An enthusiastic Boehlert summed up Congress’ actions as “in many ways, a memorial to those who lost their lives on September 11 and a tribute to their families who have joined together to advocate for this measure in the Campaign for Skyscraper Safety.”

NIST now had the money and the political backing to dig deep into the disaster. But time was critical. The first anniversary of September 11 passed with politicians vowing reconstruction as a symbolic and patriotic act. The Lower Manhattan Development Corporation, a special body created to oversee the redesign and reconstruction of the World Trade Center site, started reviewing design proposals for the next World Trade Center before the disaster experts could decisively say why the buildings had fallen.

An Unprecedented Study

After three years of research, NIST released its World Trade Center investigation in 2005. Here was the first in-depth look at how the buildings performed on September 11. The investigation focused on three main areas: the collapse of the Twin Towers, the difficulties in evacuating the buildings, and a comprehensive evaluation of the “design, construction, operation, and maintenance” of the Towers.

The collapse issue was relatively straightforward. Both Towers withstood the aircraft impacts very well, with load being efficiently redistributed to undamaged columns. The redundancy of the external framing system and the sheer scale of the buildings had allowed each to take the hit and stand. This point captured the fascination of many engineers, especially Leslie Robertson, structural engineer for the Twin Towers. Robertson took pride in the “stalwart” character of the Towers, noting in a PBS interview after September 11 that he had “designed the project for the impact of the largest airplane of its time.” Indeed, wind tunnel testing and crash modeling had been inventive aspects of the World Trade Center’s design process. To Robertson, the idea was to imagine a Boeing 707 crashing into one of the Towers, and have it withstand the collision.

Though “stalwart” in the face of a crash, the NIST report went on to detail the Towers’ startling vulnerabilities to fire. While most of the jet fuel in the planes had burned up at once, massive fires were ignited in each Tower, challenging every aspect of the fire suppression and evacuation systems. Both systems — the so called “life safety” systems — failed. Firefighters on the way up could not adequately communicate with their commanders or each other, and had to run up to the fire while occupants on the way down clambered by. Under these conditions, it is unlikely that firefighters could have put out the fire. In such an instance, the issue becomes one of time — will the buildings stand long enough for the occupants to escape? Unfortunately, closely grouped stairwells and thin stairwell walls made escape nearly impossible for the thousands trapped above the impact zones. And here the structural system — with lightweight floors designed to enable the soaring heights of the Towers — revealed the designed-in horror of the collapse. Fireproofing material applied to the structural steel had been blown off by airplane impact. The steel was exposed, the floors sagged and buckled, initiating a “progressive collapse.” As devastating as it was — with 2,753 lives taken and $100 billion in direct economic impact — there was in the NIST report a chilling side note. Given the difficulties in evacuating the Towers, if they had been fully occupied the morning of the attack, 14,000 people might have died.

Leslie Robertson admitted that the Towers’ design stage had not considered fuel load in the airplane crash scenarios. “Indeed,” he told an interviewer, “I don’t know how it could have been considered… There was no fire suppression system that could even begin to deal with that event. Nothing. Nothing.” Were the Twin Towers so unique — tall, imaginative, and ultimately so deadly — that the lessons of their collapse was inapplicable to other buildings? Here was the key question. By Robertson’s logic, there are just some contingencies for which we cannot prepare. If we want to build tall, then we must take some risks that have no remedies. By extension, if there is no way to build skyscrapers that can withstand terrorist attacks of the magnitude of September 11, then our best bet is to prevent the attacks.

Fire protection experts reject Leslie Robertson’s logic.

NIST researchers also studied a third building that had collapsed on September 11: World Trade Center 7. This much more modest building had been hit by debris, burned for hours, and collapsed late in the day. Never hit by a jetliner, WTC 7’s collapse suggested that the dangers of skyscraper fires were not limited to terrorism targets alone.

At the conclusion of their research, NIST put forward 30 detailed recommendations — from communications to fireproofing, evacuation to design principles for skyscraper safety — aimed at translating the lessons of the collapse into concrete changes for the nation’s buildings. It was the culmination of the most intense structural and fire protection investigation in American history, pushing fire testing and computer modeling of fires to the limit.

The House Science Committee convened a third hearing. Now appearing as a witness, Sally Regenhard took aim at NIST’s work. “The recommendations,” she argued, were “vague,” and “the vagueness of the language was influenced by a need for political correctness and a general reluctance or an inability to investigate, use subpoena power, lay blame, or even point out the deadly mistakes of 9/11 in the World Trade Center.”

Regenhard was particularly alarmed that the responsibility of the Port Authority of New York and New Jersey had not been adequately investigated. As owners of the land on which the Twin Towers had stood, the Port Authority enjoyed immunity from New York City building codes, and was ultimately responsible for signing off on the experimental design of the Twin Towers. Considering that the 1993 bombing demonstrated many of the same evacuation problems that were so devastating on September 11, and that fire experts had long questioned the fireproofing, Regenhard was angered by NIST’s seeming unwillingness to pursue a more aggressive investigation of negligence on the Port Authority’s part.

Experts in Action

From the September 11 attacks and collapse of the Twin Towers to the NIST study and recommendations, four years elapsed, an exceptionally short timeline from a fire safety research point of view. But this is where the pace slowed considerably, as the recommendations entered the American consensus code system.

Tangible action on NIST’s recommendations is evident, in some instances action that will redefine skyscraper design for the next generation of buildings. Fire experts agree that the most impactful change has been in design features for building evacuation. The International Building Code now requires a third exit stairway for buildings over 420 feet in height; substantial luminescent markings are now required for exit pathways in tall buildings; and stairwells must be no less than 30 feet apart, avoiding (it is hoped) the destruction of all escape pathways due to one type of impact, as happened in the Twin Towers.

Most important, skyscrapers must now also equip elevators for use in occupant evacuation. Building evacuation expert and Skyscraper Safety Campaign technical adviser Jake Pauls points out that the use of the elevator for evacuation is a much-needed “paradigm shift,” the most important change he has seen thus far in a career that stretches back to research and critique of the Towers’ evacuation design from their construction through 1993 and to the scene of the 2001 disaster. Using elevators for evacuation also opens the idea of using elevators more effectively for firefighting on high floors. On the frontier are “smart elevators” that may be programmed with building occupant information, ready to prioritize evacuation according to the special needs of occupants with disabilities, for example. Such technology would likely have saved lives on September 11.

To date, NIST reports action on 18 of its 30 recommendation areas. Clearly much remains to be done. Specifications for emergency communications systems in buildings, for example, and requirements for the adhesion of fireproofing to steel supports remain incomplete. Concerns over jurisdiction — the issue raised by Sally Regenhard regarding the Port Authority’s ability to unilaterally adopt an unproven design — remain unaddressed. But 10 years after September 11, experts at the ICC and NFPA remain positive that we will continue to see important changes flowing from the consensus code system. The process takes time, and is moving much faster than usual, a fact that representatives from every expert institution involved report is directly attributable to the lobbying of the Skyscraper Safety Campaign.

Tall Buildings Are Safe!?

“Tall Buildings are Safe!” proclaims Leslie Robertson in a recent article marking the 10th anniversary of the World Trade Center collapse. “From a structural point of view,” Robertson argues, “it isn’t realistic to think there is much you can do against large airplanes flying into tall buildings.”

Fire protection experts such as Jake Pauls worry that such a mindset is pervasive and dangerous. Over the past decade, Pauls has watched expert groups such as the ICC and NFPA “bend over backwards” in their work to learn from September 11: “What they didn’t deal with was a change of mindset — right from the beginning there was a leitmotif that what happened was not to be used for design changes. It was a special situation.”

Pauls is referring to a battle among the disaster experts over the right way to assess and control building safety going forward — not an academic issue considering we are now entering the age of the “supertall building,” with skyscrapers that dwarf the Twin Towers rising in the Middle East, across Asia, and of course on the World Trade Center site itself in the form of the planned 1,776-foot Freedom Tower.  

One of NIST’s recommendations called for the adoption of “performance-based” standards for fire and building codes. Performance-based methods would require that every building be evaluated individually not only for its structural abilities, but also for its life safety readiness. Rather than using one-size-fits-all standards, advocates of performance-based design are pushing for a close look at the unique aspects of every skyscraper before it is approved for construction. In some cases this will reveal vulnerabilities like those seen in the Twin Towers, vulnerabilities that could and should be remedied before a disaster strikes. In this view, one shared broadly throughout the fire protection engineering community, lowest common denominator “prescriptive codes” do not adequately prepare buildings as unusual as the Twin Towers for the complex dynamics of a fire.

Still, prescriptive codes today remain the norm. The NIST study demonstrated what is already possible. By using detailed structural analysis and fire protection modeling, engineers can design buildings that will both withstand major catastrophes such as a plane crash, and the major fires that might result from such an incident. Fire protection engineer Jose Torero explains that performance-based codes are well understood, but engineers like him are a minority in the larger engineering community. Currently, they have a weak voice, even with September 11 such a recent memory.

“The Leslie Robertson’s don’t understand the magnitude of the problem,” Torero worries. Structural engineers have always been focused on building skyscrapers that wouldn’t fall down, but the lesson of September 11 is that engineers need to also focus on helping first responders get to the site of a fire in a building and allowing occupants to evacuate. Further, the lesson of World Trade Center 7 is that high-rise fires can bring down buildings, whether they are attacked by planes or not. But how uniquely tailored should our procedures of design evaluation be, and how much cost will this add to a building’s construction? Again we ask: How safe is safe enough? Skyscrapers will never be safe in the opinion of engineers such as Jose Torero until the available technology of fire safety is used to its full extent. He contends that this can be done in a cost-effective way, and that performance-based design may actually reveal cost savings in many instances, cases where necessary fireproofing or structural redundancy might on close analysis be less than the prescriptive code requires. In 2011, and for the foreseeable future, this is the most divisive issue in the realm of skyscraper design.

Tall buildings are safe, but not always. This is one of the legacies of September 11 — an uncertainty on our national skyline. Looking ahead, we can expect NIST’s recommendations to drive life-safety focused upgrades to standards and building codes. In 2008, the Christian Regenhard Center for Emergency Response Studies — a center for emergency management and disaster research launched in part through a contribution from Hillary Clinton — opened at John Jay College in New York City. The work of the Skyscraper Safety Campaign goes on, as does the larger debate over safety standards in the supertall buildings of the 21st century. Whether or not the next generation of skyscrapers embraces safety along the lines advocated by Sally Regenhard, Jake Pauls, and Jose Torero remains to be seen. With the 10th anniversary of September 11 upon us, they (and we) are all hoping it won’t take another disaster to find out. • 2 September 2011

Scott Gabriel Knowles is the author of The Disaster Experts: Mastering Risk in Modern America and teaches history at Drexel University.


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