The Twin Towers: Ten Years – Ten Lessons

on Sustainable Infrastructure

Professor José Torero-Cullen FREng, FRSEBRE Trust/RAE Professor of Fire Safety Engineering

University of Edinburgh

Joint Lecture

at The Royal Society of Edinburgh

Monday 14 March 2011

Part of National Science and Engineering Week 11–20 March 2011

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The collapse of the World Trade Center towers represents one of the most dramatic failures of modern structural engineering. One of the most exhaustive and expensive failure analyses in history was conducted in the midst of speculation, controversy and conspiracy theories. In parallel, the world has seen an extraordinary evolution of the super-tall building. Seven of the ten tallest buildings in the world have been built after 9/11. These not only include the tallest four, but eight of these buildings are outside the USA. Furthermore, a strong drive towards sustainability has driven tall building design to levels of innovation never seen before. This presentation will extract, from a decade of questioning and innovation, ten lessons on what is sustainable infrastructure.

Professor Torero-Cullen originally qualified in engineering at the PontificiaUniversidad Católica of Peru, beforemoving to the University of California,Berkeley to complete his PhD.

Lecturing and research positions inFrance and the US followed, before his move to Edinburgh to head up theBuilding Research Establishment (BRE)Centre for Fire Safety Engineering atthe University in 2004.

Professor Torero-Cullen’s researchwork is in fire dynamics, structural behaviour in fire, flame spread, microgravity research, smoulderingcombustion, smoke detection and firesuppression systems. José has onductedwork on prescriptive and performance-based design, forensic fire investigationand product development. His workstrongly emphasises technology transfer and the education of firesafety engineers for the 21st Century.

José was elected a Fellow of the RoyalSociety of Edinburgh and awarded theArthur B. Guise Medal by the Societyof Fire Protection Engineers (USA) in2008, both in recognition of eminentachievement in advancing the scienceof fire protection. In 2010 he waselected a Fellow of the Royal Academyof Engineering. He is Chair of the Fire& Safety Working Group at the Councilon Tall Buildings and Urban Habitat(CTBUH) and Vice-Chair of the International Association for Fire Safety Science (IAFSS).

He has participated in landmark projects such as the NASA Space Shuttle Hangars in Florida, the 80-storey Heron Tower in London and the Clyde and Dartford Tunnel fire safety design, and in investigations of the WTC 1, 2 and 7collapses, the Madrid Windsor TowerFire, the Texas City and Buncefield Explosions, and the Ycua Bolanos supermarket fire.

He is Editor-in-Chief of Fire Safety Journal and a member of the Editorial Boards of Fire Technology,Progress in Energy and CombustionScience and Combustion Science and Technology. He is a Chartered engineer, and a member of the ASME Fire and Combustion (K-11) Committee, the UL Foams Fire Suppression Systems Committee andparticipated in the 2010 NationalAcademy of Science (USA) Decadal Review of NASA’s research agenda.

He has received numerous honours, including The European Space AgencyPost-Doctoral Research Fellowship(1993); NASA Certificate of Recognition for Outstanding Contributions to Space Shuttle Mission (1995); Lilly Center for Teaching Excellence (1996); E. RobertKent Outstanding Teaching Award(1999); Faculty Achievement Award,Office of the President (2000) and Faculty Service Award (2001) from the University of Maryland; the

William M. Carey Award for the Bestpaper Presented at the Fire Suppression and Detection Symposium,(2001); Harry C. Bigglestone Award for the Best Paper Published in Fire Technology (2002); Honorary membership of the Salamander FireProtection Engineering Society (2007);Bodycote Warrington Fire ResearchPrize for the best Fire Safety Engineering paper and the FM GlobalAward for the best paper at the 5th International Seminar on Fire and Explosion Hazards 2007. He was also awarded the Tam Dalyell Prize for Excellence in Engaging the Public with Science.

José has authored 20 book chaptersand more than 300 technical publications in a broad array of subjects associated with fire safety engineering.

The Royal Academy of Engineering and The Royal Society of Edinburgh Lecture 2011

Professor José Torero-Cullen FREng, FRSE BRE Trust/RAE Professor of Fire Safety Engineering, University of Edinburgh

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The Twin Towers: Ten Years – Ten Lessons on Sustainable Infrastructure

The history of technological evolutionis filled with failures and the lessonslearnt from them. Many will even claimthat “design by disaster” is one of themost effective methods for progress.The World Trade Center is no exception. The collapse of the WorldTrade Center buildings had the potential to question the mere natureof tall buildings and mark tall buildingdesign in ways that we could havenever anticipated. Nevertheless, tallbuilding design in the last decade wasnot driven by September 11th 2001,but by a strong impetus towards sustainability and a thriving real estatemarket. The result has been an unprecedented growth in the numberof tall buildings and unprecedentedinnovation driven by sustainability. The World Trade Center failures havenot driven the evolution of tall buildings; nevertheless, a series ofmore subtle, but no less important lessons have emerged.

Lesson 1: Sustainability is a managedlife cycle where proactive decisions aremade to reduce consumption and negative impact from the inception ofa project to the disposal of theinfrastructure. In those terms theWorld Trade Center collapses do notreflect the definition of sustainability.When addressing fire, the design oftall buildings needs to embrace theseprinciples.

Lesson 2: Fire safety is a social responsibility that guarantees the citizen a safe environment, thus it is an integral part of sustainable buildingdesign. This social responsibility hasbeen historically translated into codesand standards that establish prescriptiverequirements for buildings. These prescriptive requirements, if followedcarefully, provide the minimum level of safety required by society.

The Twin Towers: Ten Years – Ten Lessons on Sustainable InfrastructureThe nature of codes and standards is responsive, thus their development is not a driver for construction technology but a reaction to the introduction of novelideas. Because of this, there have been periods in which codes and standards had enough embedded knowledge that they could respond to all variants of construction innovation. In these periods, infrastructure can be comprehensivelyclassified into some group that is fully addressed by a specific set of rules. Fewexceptions appear outside the codes and standards and require individualised solutions. In periods of great urban or technological development, codes andstandards cannot cope with the evolution imposed by the drivers of the construction industry. In these periods, codes and standards fall behind, standardsolutions only concern few buildings and, in most cases, individualised solutionsare necessary. Explicit definitions of safety produced using engineering tools needto complement codes and standards to provide individualised solutions.

The WTC epitomised innovation, and most technical solutions were evaluatedusing the most sophisticated engineering tools of the time. Fire safety was established in a purely prescriptive manner. The last decade has been a period ofgreat innovation for tall buildings, thus fire safety cannot be based on a purelyprescriptive analysis.

Lesson 3: Sustainability requires building in the infrastructure’s life cycle throughan optimised design process. The WTC did not optimise fire safety within thestructural design process, thus it was not optimised correctly. The failure to understand the structural behaviour in fire resulted in disproportionate and unpredictable consequences. Tall buildings are by nature optimised structures,thus their design needs to incorporate fire safety as an integral design component.

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The Royal Academy of Engineering and The Royal Society of Edinburgh Lecture 2011

Lesson 6: Innovation introduces complexity, thus the drive for sustainable tall buildings is introducing fundamentalchanges in structural design, material selection and potentialfire conditions. The WTC demonstrated that to establishan adequate fire safety strategy,there was a need for professionals of great knowledgein all fields involved. Questions of competence emerged when the analysis of recognised professionals was put into question. What does a structuralengineer need to know to beable to design a tall building thatwill be safe in a fire? What doesa fire safety engineer need toknow to be able to design aproper fire safety strategy for tallbuildings? Sustainable tall buildings require the involvementof professionals competent in thedesign of a comprehensive firesafety strategy.

Lesson 5: Sustainability is about shared responsibility.WTC showed that the responsibility for integrating structural integrity to the fire safety strategy was undefined. While in a prescriptive environment the architect is responsible for the definition of thermal protection to the structure, nobody is responsible for theassurance that the structure will perform adequately. Theimplicit assumption that thermal protection is sufficient to guarantee safety was proven inadequate. For tall buildings, the structural engineer needs to assumeresponsibility for the adequate performance of the structure in a fire.

Lesson 4: Sustainability requires optimised utilisation of tools and resources. Problems need to be understood and resolved by means of the most adequate methodologies. The WTC demonstrated that, for tall buildings, egress and structural performance are the pillars on which fire safety stands. But for tall buildings, egress is of a similar time scale to the deterioration of the structure by the fire. Thus, both components of the fire safety strategy are coupled. Egress times can be reduced but, for tall buildings, they can never be made much shorter than structural failure times. Thus improvements in egress can be legislated through code requirements. In contrast, innovative structures need a proper engineering analysis, because they do not conform to standard practices but mainlybecause their integrity is the guarantee for safe egress. In the absence of an adequate structural design, enhanced egress capabilities cannot be used as compensation. The safety of tall buildings requires an explicit structural analysis onducted using state-of-the-art engineering tools.

Lesson 7: Throughout the WTC investigation, it becamevery clear that the framework educating professionals involved in the design of innovative buildings leaves a gap of knowledge when it comes to the assessment ofsafety. It is designed to operate within a prescriptive environment and does not incorporate the knowledgebase necessary for engineering-based safety. If we are to continue to strive for sustainable infrastructure and the associated innovation, then we need to support the development of an educational framework that will enable our professionals to deliver safe infrastructure. The current framework is not sustainable.

Burj el Khalifa in Dubai, opened in January 2010. Thetallest man-made structure to date at 828 m with 163habitable floors.(Image from Wikimedia Commons)

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The Twin Towers: Ten Years – Ten Lessons on Sustainable Infrastructure

Lesson 8: The WTC showed that welack an adequate definition of competence. Our current definition ofcompetence not only leaves enormousknowledge gaps, but also is structuredaround incorrect objectives. The development of sustainable tall buildings needs a definition of who iscompetent to deliver the engineeredfire safety strategy.

Lesson 9: Extracting from a failure allthe knowledge that will enable professionals not to make the samemistakes requires a minimum level ofprior understanding. The most successful investigations are those conducted in an atmosphere where allthose involved have sufficient knowledge to make the most of theinvestigation and to transfer that newknowledge into the design process. Inthe past, fire investigations have beenconducted in such an atmosphere. The unprecedented magnitude andnovelty of the WTC failure caught thefire safety and structural communitiesunprepared for the investigation. Thus,over the last decade, these professional communities have produced the science to unveil manyof the phenomena, but not to transform that knowledge into designmethodologies and tools. The gaps ofknowledge are now evident; thus thefuture of tall building design dependson our capability to continue fillingthese knowledge gaps at a pace fasterthan our capability to innovate.

Lesson 10: The WTC showed that if we want sustainable tall buildings, we needto develop the knowledge base and the technological tools that can adequatelyassess the performance of a fire safety strategy. We need to incorporate thisknowledge, not by legislating new rules, but through adequate professionalsstructured within a relevant definition of competence. We need to legislate competence, not standardised solutions.

The Jin Mao Tower – 421 m –88-storey landmark in Shanghai,constructed 1994–1999

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The Royal Academy of Engineering and The Royal Society of Edinburgh Lecture

The Royal Society of Edinburgh

The Royal Society of Edinburgh (RSE) is Scotland’s National Academy of Science & Letters. It is an independent body with charitable status. The Society organises conferences and lectures for the specialist and for the general public. It provides a forum for informed debate on issues of national and international importance. Its multidisciplinary Fellowship of men and women of international standing provides independent, expert advice to key decision-making bodies, including Government and Parliament.

The Society’s Research Awards programme annually awards over £2 million to exceptionally talented young researchers to advance fundamental knowledge, and to develop potential entrepreneurs to commercialise their researchand boost wealth generation.

Among its many public benefit activities, the RSE is active in classrooms from the Borders to the Northern Isles,with a successful programme of lectures and hands-on workshops for primary and secondary school pupils.

The Royal Society of Edinburgh, working as part of the UK and within a global context, is committed to the future of Scotland’s social, economic and cultural wellbeing.

The Royal Acacemy of Engineering

"As Britain’s national academy for engineering, we bring together the country’s most eminent engineers from all disciplines to promote excellence in the science, art and practice of engineering. Our strategic priorities are to enhance the UK’s engineering capabilities; to celebrate excellence and inspire the next generation; and to lead debate by guiding informed thinking and influencing public policy."

Strategic PrioritiesThe Academy’s work programmes are driven by three strategic priorities, each of which provides a key contribution to a strong and vibrant engineering sector and to the health and wealth of society.

Enhancing national capabilitiesAs a priority, we encourage, support and facilitate links between academia and industry. Through targeted national and international programmes, we enhance – and reflect abroad – the UK’s performance in the application of science, technology transfer, and the promotion and exploitation of innovation. We support high-quality engineering research, encourage an interdisciplinary ethos, facilitate international exchange and provide means of determining and disseminating best practice. In particular, our activities focus on complex and multidisciplinary areas of rapid development.

Recognising excellence and inspiring the next generationExcellence breeds excellence. We celebrate engineering excellence and use it to inspire, support and challengetomorrow’s engineering leaders. We focus our initiatives to develop excellence and through creative and collaborative activity, we demonstrate to the young, and those who influence them, the relevance of engineering to society.

Leading debateUsing the leadership and expertise of our Fellowship, we guide informed thinking; influence public policy making; provide a forum for the mutual exchange of ideas; and pursue effective engagement with society onmatters within our competence. The Academy advocates progressive, forward-looking solutions based on impartial advice and quality foundations, and works to enhance appreciation of the positive role of engineeringand its contribution to the economic strength of the nation.

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The University of Edinburgh has been an important institution in the field of Fire Safety Engineering forover three decades. Many of those who are now leaders in the field came to Edinburgh to study and research under the supervision of the late ProfessorDavid Rasbash, one of the main pioneers of the discipline, and Professor Dougal Drysdale, author ofthe definitive text book on the subject, Introduction to Fire Dynamics (Wiley, 2nd edition 1998).

Teaching and research in fire safety continues at Edinburgh under the leadership of Professor JoséTorero-Cullen, appointed to the BRE/RAE Chair in Fire Safety Engineering in 2004.

The BRE Centre for Fire Safety Engineering is part of the Institute for Infrastructure and Environment,School of Engineering at The University of Edinburgh.

This group of fire safety engineering experts represents a world-class research fire centre, with 40 research members from more than 18 different nationalities.

The BRE Centre for Fire Safety Engineering exists to:

•Equip tomorrow's leaders in the field with the skills they require

•Support today's fire safety with multidisciplinary research

•Provide first-class education in Fire Safety Engineering and Stuctural Fire Engineering

•Deliver fire safety consultancy services to industry and other consultancies

•Disseminate information about advances and research in fire safety engineering through courses,symposia and publications

They consult to fire safety and building consultantsworldwide in a commercial capacity. Advice from the group is invaluable, both to commercial operators in the construction and engineering sector and also to public bodies concerned with health and safety regulation.

The Twin Towers: Ten Years – Ten Lessons on Sustainable Infrastructure

Contact:The Royal Society of Edinburgh – www.royalsoced.org.uk – 0131 240 5000The Royal Academy of Engineering – www.raeng.org.uk – 020 7766 0600

BRE Centre for Fire Safety Engineering, University of Edinburgh –www.see.ed.ac.uk/fire/

National Science and Engineering Week – www.britishscienceassociation.org/web/

The Royal Academy of Engineering/The Royal Society of Edinburgh

Joint Lecture 2011ISBN No 978 0 902198 56 2

© The Royal Society of EdinburghMarch 2011

The Royal Society of Edinburgh, Scotland’s National Academy, is Scottish Charity No SC000470The Royal Academy of Engineering is Registered Charity No 293074