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1
Introduction

On February 26, 1993, the World Trade Center towers in New York City, two of the tallest buildings in the world and an instantly recognizable symbol of the United States, were the target of a terrorist car bomb. Six people were killed, scores were injured, and the damage to the structure and its contents would cost many hundreds of millions of dollars to repair. Two years later, on April 19, 1995, the Alfred P. Murrah Federal Building in downtown Oklahoma City was the target of an even more devastating and deadly attack.

Such bomb attacks have become a familiar feature of modern life around the world. In the past few years, there have been explosions in the financial center of London, and in Buenos Aires a multistory community center was destroyed, resulting in major loss of life. The technology to produce powerful explosives is relatively simple and inexpensive. Delivery can be as easy as parking a car or van under or near a building, or by walking into a building with a briefcase or package.

What can be done to mitigate the effects of explosions that do occur? Several federal agencies, including the Defense Nuclear Agency (DNA) and the U.S. Army Corps of Engineers (USACE), have for many years studied explosions and their effects on structures of various kinds. It is reasonable, therefore, to inquire about all the information developed for military use and how that information might be applicable to the civilian sector. The director of DNA, in cooperation with the director of the Waterways Experiment Station (WES), USACE, asked the National Research Council (NRC) to undertake a study to recommend policy and technical advice on transferring to the civilian sector the applicable security technologies developed by DNA, USACE, and other federal agencies.



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Page 4 1 Introduction On February 26, 1993, the World Trade Center towers in New York City, two of the tallest buildings in the world and an instantly recognizable symbol of the United States, were the target of a terrorist car bomb. Six people were killed, scores were injured, and the damage to the structure and its contents would cost many hundreds of millions of dollars to repair. Two years later, on April 19, 1995, the Alfred P. Murrah Federal Building in downtown Oklahoma City was the target of an even more devastating and deadly attack. Such bomb attacks have become a familiar feature of modern life around the world. In the past few years, there have been explosions in the financial center of London, and in Buenos Aires a multistory community center was destroyed, resulting in major loss of life. The technology to produce powerful explosives is relatively simple and inexpensive. Delivery can be as easy as parking a car or van under or near a building, or by walking into a building with a briefcase or package. What can be done to mitigate the effects of explosions that do occur? Several federal agencies, including the Defense Nuclear Agency (DNA) and the U.S. Army Corps of Engineers (USACE), have for many years studied explosions and their effects on structures of various kinds. It is reasonable, therefore, to inquire about all the information developed for military use and how that information might be applicable to the civilian sector. The director of DNA, in cooperation with the director of the Waterways Experiment Station (WES), USACE, asked the National Research Council (NRC) to undertake a study to recommend policy and technical advice on transferring to the civilian sector the applicable security technologies developed by DNA, USACE, and other federal agencies.

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Page 5 Scope of the Study In response to that request, the NRC established the authoring committee of this report and charged the committee with the following specific tasks: • Identify, document, and review the body of knowledge on blast-mitigating technologies and the design methodologies used to minimize or mitigate blast-effects on internal building structures and relevant subsystems. • Assess this body of knowledge as it might apply to conventionally designed existing civilian office buildings. Identify gaps in knowledge, needed research and development, and other appropriate actions to further develop and apply promising technologies and design methodologies in the civilian sector. • Recommend steps, such as research and development, education and training programs, or policy changes within or applying to the military agencies, that would be needed to implement promising civilian applications. This report considers non-nuclear explosions and their effects (including fire and smoke) on multistory commercial buildings and facilities; however, much of the information presented here should have wider applicability to civilian building design. Prevention of explosions through the use of perimeter access-control security systems to limit entry of bombs and to detect those that get through before they are detonated is discussed only superficially. There is an extensive body of knowledge concerning the design and application of active security systems which the committee has judged to exceed the scope of its charge. For similar reasons, the committee also did not address the potential effects of chemical or biological weapons. At the outset, the committee was aware that techniques for hardened military construction, developed over many years by the U.S. Department of Defense, focus on maintaining the structural integrity of a principal facility at some designated threat level in order to sustain operation of mission-critical equipment and personnel within. Usually the facility is located and constructed in a way to reduce the likelihood of attack (e.g., buried missile silos, underground command centers) and further protected through controlled access, bomb detection, and other passive and active security measures. Moreover, since the primary structural envelope of a blast-hardened military facility is not intended to be breached by a bomb explosion at design threat levels, little consideration is given to the blast resistance and failure characteristics of critical building life-support subsystems such as lighting, communications, and ventilation. Clearly, many of these design approaches are characteristic of military construction and are neither desirable nor practical for civilian buildings that provide ready access and a friendly atmosphere to the public and where prevention of injury and loss of life is of paramount importance under emergency situations. The more appropriate perspective for civilian buildings design professionals

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Page 6 might be that, since little can be done to thwart the determined terrorist bomber, how can the building be designed and constructed in ways that can reduce hazards to people and enhance safe rescue and repair efforts? This question has been uppermost in the committee's deliberations in dealing with the second of the three tasks stated above. Organization of the Report The succeeding chapters in this report address the study's charge in the following manner: Chapter 2 presents a fundamental background on the motives, methods, and immediate results of terrorist activities, including such topics as statistical patterns of recent terrorist acts, the types of damage to structures and critical building systems, and injuries that can be expected after a bomb detonates. Chapter 3 summarizes relevant knowledge on blast-effects mitigation and protective design technologies, including both empirical techniques and numerical simulations, which in the committee's judgment are applicable to civilian architecture. The scope of the committee's charge did not include an exhaustive assessment or review of the state of the art of all hardening and protective design methodologies. The committee did, however, elicit and receive numerous briefings from the sponsors and their principal contractors concerning all relevant past and current research and development in this area, and has utilized this information in generating its findings and recommendations. Chapter 4 explores the potential opportunities to transfer blast-effects mitigation technologies in such areas as architectural planning and design and placement of building systems, along with possible transfer agents and economic issues for the transfer process. The study's findings and recommendations are presented in Chapter 5.