Executive Summary

INTRODUCTION

In recent years, explosives have been used maliciously in various ways for a variety of different reasons. Of particular concern in the United States are bombing incidents—such as the bombing of the World Trade Center in New York City in 1993 and of the Alfred P. Murrah Federal Building in Oklahoma City in 1995—that result in the death or injury of large numbers of innocent victims. High-visibility terrorist incidents targeting innocent individuals have also led to considerable loss of life in bombing attacks on airplanes, cars, and buildings throughout the world (U.S. Department of State, 1996).

In response to requirements in the Antiterrorism and Effective Death Penalty Act of 1996 (P.L. 104-132), the Committee on Marking, Rendering Inert, and Licensing of Explosive Materials was charged with considering the advisability of physically altering explosive materials and of controlling access to them for the purpose of suppressing illicit use of explosives. More specifically, the committee was asked to (1) evaluate the technical feasibility and practicality of using markers for detection, taggants for identification, and inertants for desensitization of explosives and (2) assess the implications of imposing regulatory controls on a prioritized set of precursor chemicals. Black and smokeless powders, among the explosives used most often for illegal purposes (ATF, 1995), were specifically excluded from this study by the enabling legislation.

In approaching its task, the committee quickly became aware of two currently relevant factors that must be taken into account in assessing how to deal effectively with the threat of illegal bombing attacks in this country:



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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors Executive Summary INTRODUCTION In recent years, explosives have been used maliciously in various ways for a variety of different reasons. Of particular concern in the United States are bombing incidents—such as the bombing of the World Trade Center in New York City in 1993 and of the Alfred P. Murrah Federal Building in Oklahoma City in 1995—that result in the death or injury of large numbers of innocent victims. High-visibility terrorist incidents targeting innocent individuals have also led to considerable loss of life in bombing attacks on airplanes, cars, and buildings throughout the world (U.S. Department of State, 1996). In response to requirements in the Antiterrorism and Effective Death Penalty Act of 1996 (P.L. 104-132), the Committee on Marking, Rendering Inert, and Licensing of Explosive Materials was charged with considering the advisability of physically altering explosive materials and of controlling access to them for the purpose of suppressing illicit use of explosives. More specifically, the committee was asked to (1) evaluate the technical feasibility and practicality of using markers for detection, taggants for identification, and inertants for desensitization of explosives and (2) assess the implications of imposing regulatory controls on a prioritized set of precursor chemicals. Black and smokeless powders, among the explosives used most often for illegal purposes (ATF, 1995), were specifically excluded from this study by the enabling legislation. In approaching its task, the committee quickly became aware of two currently relevant factors that must be taken into account in assessing how to deal effectively with the threat of illegal bombing attacks in this country:

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors Insufficiency of data on bombings. For technical evaluations, cost-benefit analyses, and formulation of a technically detailed rational response strategy, the data available today on illegal use of explosive materials in the United States do not constitute a suitable basis for a complete scientific analysis.1 For example, the annual bombing statistics reported by the Federal Bureau of Investigation and by the Bureau of Alcohol, Tobacco, and Firearms differ somewhat. In addition, neither agency maintains complete records on the frequency of illegal use of common explosive chemicals, and neither was in a position to supply for this study definitive, statistically sound information on sources of stolen commercial explosives used in bombings. It is important that the Congress be kept well informed on changing patterns and trends in illegal use of explosives so that appropriate actions can be taken in accord with a planned national strategy. Clearly, a single national data bank for incidents involving stolen explosives and criminal bombings—requiring uniform and detailed reporting from local, state, and federal investigators and organized so that interpretive correlations and trends in criminal activity could be readily extracted—would be of much value in developing a rational, broad-based approach to containing illegal bombing attacks in the United States. Such a data bank would emphasize significant bombing incidents but might also track nuisance bombings. Need for ongoing rigorous testing of additives proposed for use with explosives. Although some of the concepts now being proposed for altering explosives are technically feasible, none has been satisfactorily proven to have practical efficacy for broad use as a means to control illegal bombings. More research and development are necessary to find new approaches and to improve those that currently hold the most promise for future use. Also needed are extensive research and testing to address complex questions of safety, industrial practicality, affordability, and environmental impacts before implementation of any of the proposed concepts could be advised. Moreover, because of the risks associated with manufacturing, transporting, and using explosives, industries that produce or rely on these materials would have to be assured that any changes in their standard procedures represent modifications validated by vigorous testing. 1    The overall lack of sufficient, relevant, statistically valid data has persisted for two decades. In 1980, when it was engaged in examining the use of taggants in explosives, the Office of Technology Assessment (OTA) found that, despite the availability of computerized data banks, it was not possible to retrieve and analyze the data in a meaningful way. Furthermore, "the files did not contain all the data needed for the OTA analysis" (OTA, 1980, p. 233).

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors DEVISING A THREAT-BASED STRATEGY FOR CONTROLLING ILLEGAL USE OF EXPLOSIVES Few would disagree with implementation of an "ideal" technology that would prevent bombings provided that all costs—financial, social, legal, and environmental—were acceptable. As these costs accumulate, however, any proposed technology or concept must be scrutinized and its likely effects weighed to ensure a favorable balance between costs and benefits. In examining how explosives might be controlled by technological means—marking for detection, tagging for preblast and postblast identification, and inerting by the use of additives—or by regulation, the committee found that a wide range of options is available. Recognizing that the threat of bombing attacks is likely to continue but may vary in nature and severity, the committee scaled its recommended options so that they can be applied in a manner appropriate to the assessed level of threat to the public.2 A major escalation of terrorism against the U.S. public and government, for example, might merit emergency controls as a suitable response. At a lower level of threat, however, the disruption of legitimate industries (chemicals, explosives, mining, and others) owing to such a program would be too costly. In considering the threat posed by illegal use of explosives in the United States, the committee has emphasized the lives lost and property damage per incident. In fact, the World Trade Center and Murrah Federal Building bombings were the precipitating events for this study. In addition, an assessment of bombing threat level must also reflect other considerations, including the public's perception of its vulnerability to bombings. The committee emphasizes that it will be policymakers—not the committee—who will determine what constitutes a specific level of threat. Basic to a workable national strategy is the importance of maintaining a flexible approach to any required use of detection markers, identification taggants, and inertants, as well as to regulation of access to explosives and their chemical precursors. Bombers have demonstrated that they can change their tactics in response to the implementation of controls or shifts in the availability of particular chemicals or precursors. In addition, their expertise and level of sophistication 2    The committee is, of course, mindful that responses to an assessment of increased threat cannot for the most part be instantaneous. The committee did not try to describe a threat-response scenario that could be implemented on a real-time basis but instead attempted to provide a range of options to choose from depending on the seriousness of the threat from illegal bombings as judged by policymakers. These options include a series of research efforts that should be undertaken now, so that responses could be quickly implemented should the need arise. But other options would necessarily require time for the normal process of developing any new technical capabilities, programs, or federal regulations and policies that might be considered essential. The committee did not attempt to estimate implementation times for such options.

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors may increase because of the detailed information on bomb making now available on the Internet, as well as from other sources. IMPROVING THE CAPABILITY TO DETECT EXPLOSIVES In assessing technical approaches to controlling the criminal use of explosives, the committee gave high priority to methods of detecting a bomb before it explodes. Preblast detection can be accomplished by (1) detecting a material added to an explosive—the detection marker—or (2) directly detecting the unmarked explosive itself through probing its mass or by trace detection of residues and vapors emitted by the explosive. Although it is somewhat more difficult, the direct detection of unmarked explosives is clearly preferable, because the potential bomber will continue to have illegal access to unmarked explosives, and their use in that form must thus be anticipated. Following the bombing of Pan American World Airways flight 103 in 1988, priority was given to screening passengers and baggage at airports because of the potential for significant loss of life from bombs made with small quantities of high explosives. Advances in analytical instrumentation have made direct detection of trace quantities of explosives relatively easy under laboratory conditions. However, it is difficult to detect small amounts (typically, a few pounds) of concealed plastic or sheet explosives, which is all that may be required to destroy an airliner. Plastic and sheet explosives are usually manufactured with RDX3 or PETN4 as the primary energetic ingredient. Each of these materials has a very low vapor pressure and is difficult to detect with vapor detectors, but the addition of volatile chemical markers makes plastic and sheet explosives detectable by inexpensive commercial equipment. Accordingly, the Ad Hoc Group of Specialists on the Detection of Explosives, which reports to the U.N. Council of the International Civil Aviation Organization (ICAO), proposed that volatile marker chemicals be added to plastic and sheet explosives during manufacture. Four detection markers were identified, and in March 1991 the ICAO Convention on the Marking of Plastic Explosives for the Purpose of Detection was signed by 39 nations (ICAO, 1991). The Antiterrorism and Effective Death Penalty Act of 1996, the enabling legislation for U.S. ratification, took effect on April 27, 1997. The ICAO Convention, anticipated to go into effect in 1998, provides only for the marking of plastic and sheet explosives. The capabilities for detecting unmarked explosives have improved significantly in the last decade, and continued improvement is expected. The committee believes that the desirability of adding detection markers to explosives to enhance 3    RDX is the high explosive 1,3,5-trinitro-1,3,5-triazacyclohexane. 4    PETN is the high explosive pentaerythritol tetranitrate.

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors their detectability must be evaluated in the context of this improving capability to detect unmarked explosives. Conclusions 2,3-Dimethyl-2,3-dinitrobutane (DMNB) has been identified as a viable vapor detection marker to be added in low concentrations to plastic and sheet explosives. Its use is in full accord with the ICAO Convention, ratified by the United States in April 1997, which requires the detection marking of plastic and sheet explosives with one of four volatile compounds. The potential presence in terrorist hands of unmarked explosives from a variety of noncommercial sources is a flaw in any marking approach where no provisions are made to detect the unmarked explosive as well. The addition of detection markers to any or all explosives would not address existing stocks of unmarked nonmilitary explosives diverted from the normal stream of commerce, unmarked military explosives, unmarked explosives provided by a state sponsor of terrorism, or unmarked improvised explosives. The technology available to detect unmarked explosives is improving rapidly, so that it is now increasingly possible to detect a broad range of explosives in many scenarios. Future improvements will allow the extension of this capability to a wider range of applications. Recommendations Strategic national investment should focus on the detection of unmarked explosives. This broad effort should include the following actions: Deploying detection equipment based on existing technology to other critical sectors beyond airports;5 Accelerating the engineering effort to make current detection equipment less costly and easier to implement, thus enabling wider operational deployment; and Conducting research leading to the development of new or improved techniques to detect unmarked explosives. 5    The committee made no attempt to identify which facilities might be priority candidates for explosives detection systems; such facilities might include federal courthouses, government offices, large public facilities, and power generation and transmission facilities, among others. Policymakers will make these decisions based on the cost of the detectors, their effectiveness in detecting bombs, and policymakers' assessment of the bombing threat level.

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors Emphasis should be placed on and resources directed toward the deployment of existing explosives detection technology capable of detecting ICAO markers and unmarked explosives. Research on the detection of unmarked explosives is currently under way under the direction of the Federal Aviation Administration (for aviation applications), the Interagency Technical Support Working Group (for federal applications), and the National Institute of Justice (for civilian law enforcement applications). The addition of detection markers to explosives beyond that required by the International Civil Aviation Organization Convention is not recommended at the present time. More than 5 billion pounds of commercial explosives (the majority of which cost $0.10 to $0.15 per pound) are used annually in the United States. The cost of marking with DMNB is projected to reach a lower limit of $0.02 to $0.20 per pound for, respectively, a 0.1 to 1 percent marking level. This cost increment, together with the cross-contamination concerns associated with widespread distribution of the marker in the environment, would appear to rule out the use of markers such as DMNB for all but the most high-value commercial explosives. The United States should conduct research on the use of International Civil Aviation Organization markers (or similar markers that can be detected by the same equipment) in commercial boosters, detonating cord, and other low-vapor-pressure, cap-sensitive commercial explosives . Currently these critical components, used in the fabrication of terrorist explosive devices, are not easily detectable. If technically feasible, the capability for marking these components of explosives should be ready for implementation in the event that the threat of illegal bombings escalates. Such research might be carried out jointly by the Department of Defense and commercial explosives manufacturers. The United States should conduct research leading to a commercial prototype system for the production and detection of detonators and/or explosives marked with coincident gamma-ray emitters. The coincident gamma-ray marking approach has great promise, but more operational information must be collected and evaluated before deployment can be considered. Research should be conducted to examine the real and perceived health hazards of the radioactive marker in manufacture, storage, and use. Methods of incorporation of the marker into detonators and methods of detection should be validated through a full-scale demonstration program. This option should be available for implementation if the bombing threat escalates. Some research in this area is currently being conducted within the Department of Energy.

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors TAGGANTS FOR PREBLAST AND POSTBLAST IDENTIFICATION OF EXPLOSIVES The committee examined a variety of concepts for identification taggants, additives that can provide information, both before and after a blast, about the nature and source of an explosive. Designed to survive a blast and to be recovered at the site of an explosion, an identification taggant can help law enforcement officials to trace an explosive's transfer from the manufacturer, through intermediaries, and finally to the bomber. In its assessment, the committee focused particularly on the ability of a taggant to supply postblast information that would be useful to law enforcement in identifying and prosecuting bombers, and that therefore might have a deterrent effect. The various taggant concepts described to the committee can be classified broadly as particulate, isotopic, or biological. Although a number of these appear promising, the information currently available about nearly all of the taggant concepts is inadequate to evaluate their effectiveness in real operational or economic terms. More research and development are needed to find new approaches and to improve those that currently hold the most promise for future use before implementation could be advised. Only one taggant has been subjected to extensive testing in the United States (Aerospace, 1980b), and this taggant, now manufactured by Microtrace Inc., is currently in use by the Swiss explosives industry (Schärer, 1996). The committee would, of course, recommend the use of any "ideal" taggant that met all of the necessary technical and economic requirements, if the threat to society justified the costs of its implementation. No taggant known to the committee realizes this standard. The Microtrace taggant, manufactured originally by the 3M Company, was the subject of a 1980 Office of Technology Assessment report (OTA, 1980) and has been in commercial use in Switzerland for 18 years following adoption by the Swiss of the Federal Act on Explosives for Civil Purposes (Schärer, 1996).6 Even with this comparatively extensive background of study and use, the economic, environmental, and other costs associated with this taggant make its adoption as a universally acceptable taggant unlikely. This committee's assessment of identification taggants was aided considerably by discussions with appropriate officials in Switzerland.7 However, applications in Switzerland are different from those envisioned for the United States, and 6   The related legislation includes the Federal Law on Explosive Materials (explosives law) of March 25, 1977, enacted by the Federal Assembly of the Confederation of Switzerland, and the Order Concerning Explosive Materials (explosives regulation) of March 26, 1980, issued by the Swiss Federal Council. 7   See Appendix F, "Summary of European Site Visit."

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors many questions remain unanswered concerning the practical use of taggants in this country. For example, the Swiss explosives market is more narrowly defined than that in the United States, and nearly all Swiss explosives are packaged. The U.S. situation is much more complex, with a several-hundredfold-larger market for explosive materials, a wider range of products, and broader use of explosives in legitimate industries. In the United States, for instance, explosives are used in virtually all mining operations, whereas no comparable mining is done in Switzerland. Conclusions It is technically feasible to tag some explosives for identification. The Office of Technology Assessment report (OTA, 1980) and the Swiss experience (Schärer, 1996) show that some explosives can be usefully tagged. The additional diversity and larger scale of U.S. uses of explosives mean that the Swiss experience does not provide definitive guidance for the U.S. deployment of taggants. Identification taggants could provide an additional tool to law enforcement in solving and prosecuting criminal cases. Depending on the thoroughness of the sales and distribution records maintained, the information encoded by taggants might aid in identifying the type and source of an explosive used illegally. Also, the presence of taggants could be of value in linking explosives recovered in a suspect's possession to those used in a criminal act, although there are unresolved legal issues associated with the use of such evidence in criminal proceedings. Technical criteria must be considered in the evaluation of any taggant concept. These criteria are safety in manufacture and use, effect on the performance of explosives products, utility for law enforcement (including ease of countermeasures, cross-contamination problems, forensic and prosecutorial utility, and blast survivability), environmental acceptability, immunity from contamination of the mined product, costs (of the taggant material, processing, and record keeping), and universal applicability. Only one taggant concept—a particulate, coded material—has been subjected to extensive technical evaluation and has a long-term history of use. In the late 1970s the Bureau of Alcohol, Tobacco, and Firearms funded an Aerospace Corporation evaluation of the Microtrace taggant (Aerospace, 1980b). In addition, this taggant has been used for identification tagging of explosives in Switzerland since 1980 (Schärer, 1996). Other taggant concepts have been proposed but have not gone beyond the research and development phase. Several taggant concepts presented to the committee require the introduction of the taggant into the explosive at a level of

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors no more than a few parts per million. Additives at such low levels are likely to come sufficiently close to meeting the requisite taggant technical criteria, but a recommendation for adding these identification taggants cannot be made at this time without successful demonstration and testing against these criteria. Costs weigh against broad-based U.S. implementation of a taggant program. Uncertainties about long-term persistence in the environment, product contamination, range of costs, and possible safety issues argue against broad-based implementation of the particulate tagging of explosives (including ammonium nitrate) at the present time. A taggant program limited to cap-sensitive explosives would pose fewer concerns regarding costs, persistence in the environment, and product contamination than would a program for tagging blasting agents and bulk ammonium nitrate. Since ammonium nitrate cannot be detonated without a detonator and a cap-sensitive booster, tagging these components could offer forensic value comparable to that of tagging ammonium nitrate without disrupting the manufacture and handling of this high-volume chemical. Similar arguments apply to tagging packaged cap-sensitive explosives, which represent a small fraction of the market for all commercial explosives. Using distinct taggant types for different classes of commercial explosives could complicate collection, recovery, and analytical protocols. Training and equipment requirements, time for investigation, and costs weigh against the use of multiple taggant concepts. Furthermore, premature introduction of taggant concepts could stifle the development of superior methods later. Recommendations Identification tagging of explosives should not be required at the present time. Although tagging is technically feasible, the costs of a tagging program do not currently appear to be justified on the basis of the potential benefits. A research program should be carried out to identify, evaluate, and develop a taggant system that meets several technical criteria. These criteria are safety in manufacture and use, effect on the performance of explosives products, utility for law enforcement (including resistance to countermeasures, lack of cross-contamination, forensic and prosecutorial utility, and blast survivability), environmental acceptability, immunity from contamination of the mined product, costs (of the taggant material, processing, and record keeping), and universal applicability. Such a taggant system should be available for use in case the bombing threat level rises.

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors If the bombing threat level increases owing to greater use of packaged, cap-sensitive explosives as the main charge or booster in bombs that cause injury, death, or major property damage, a program should be implemented to tag these explosives using the best available technology, provided that the chosen taggant technology has satisfactorily met all the appropriate technical criteria. The types of explosive materials to be tagged should be those contributing to an increased (current and projected) bombing threat level. From 1991 to 1995, on average, commercial high explosives were used as a main charge in only a low percentage of U.S. explosive bombings. To the extent that commercial high explosives are used as initiators or boosters in improvised bombs, tagging them might also help to solve these cases. Appropriate testing would be necessary to ensure the feasibility of this approach, including recovery testing of the taggants. RENDERING EXPLOSIVE MATERIALS INERT Many common chemicals could potentially be used as explosives in bombs, but a careful review by the committee showed that ammonium nitrate, used in the bombing of the Murrah Federal Building in Oklahoma City, is by far the most commonly accessible explosive material. The committee therefore gave special attention to steps that might reduce the danger from large bombs with ammonium nitrate as the main component. Several other chemicals were considered but were judged to be of lesser concern. Ammonium nitrate is produced in enormous quantities for use both as a fertilizer and as an ingredient in legitimate blasting agents, and so it is difficult to prevent its acquisition by bombers. Despite considerable international effort to reduce fertilizer-grade ammonium nitrate's effectiveness as an explosive or to render it inert, no currently known technique or technology would drastically reduce its explosive potential in large illegal bombs without seriously affecting its use as a fertilizer. A variety of other strategies, both technical and regulatory,8 have been used in Northern Ireland to raise the barrier to obtaining pure ammonium nitrate. The committee discussed with British law enforcement personnel their experience in dealing with terrorist bombings (see Appendix F). These discussions were informative about attempts to control access to explosives, especially by rendering ammonium nitrate inert. Although the British experience does not 8   Applicable regulations include the Statutory Rules and Orders of Northern Ireland, No. 118, Explosives: Control of Ammonium Nitrate, Ammonium Nitrate Mixtures, and Sodium Chlorate; No. 218, Control of Nitrobenzene; No. 171, Explosives Regulations; No. 463, Control of Sodium Chlorite; No. 32, Control of Potassium Nitrate and Sodium Nitrate; and No. 51, Control of Sodium Nitrite, 1972-1981.

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors provide a remedy that is directly applicable to U.S. problems, it does yield valuable information about what does and does not work under field conditions. In principle, explosive chemicals might be rendered inert by adding a chemical suppressant or diluent or by changing the explosive's physical form. Alternatively, energetic materials might be desensitized to reduce their explosive potential or make them more difficult to detonate, much as textiles or polymers are made less flammable by the addition of fire retardants. In fact, many methods have been attempted for making ammonium nitrate fertilizer inert to detonation, including the addition of limestone in Northern Ireland. To date, techniques to defeat attempts at inerting have always been found. Following the bombing of the Murrah Federal Building, methods to render ammonium nitrate nondetonable were discussed in congressional hearings. One such method was based on a patent issued in 1968 to S.J. Porter.9 The patent claims a method of rendering fertilizer-grade ammonium nitrate resistant to flame and insensitive to detonation by adding 5 to 10 percent of mono-and diammonium phosphate or a mixture thereof with potassium chloride or ammonium sulfate. However, subsequent tests showed that mixtures of ammonium nitrate containing the Porter additives were detonable when tested in sufficiently large charge diameters (Eck, 1995). The original Porter tests had been performed on small charge sizes, with minimal confinement and minimal booster materials. This result demonstrates the importance of performing evaluation testing under appropriate test conditions. Clearly, there is great incentive to identify an additive that, when added in small percentages, could render ammonium nitrate or other energetic chemicals inert to detonation. Research is now being conducted in the United States and in Great Britain, but no such additive has yet been identified. Conclusions Although a number of common chemicals could be used in illegal bombings, the common explosive chemical likely to be of greatest threat is ammonium nitrate. The committee's qualitative ranking of common explosive chemicals, based on availability and accessibility, ease of bomb making, cost, and history of prior use, indicated that ammonium nitrate (AN) is by far the most obvious material for making large bombs. Despite ongoing research in both the United States and abroad, no practical method for inerting ammonium nitrate has yet been found. No additive (such as claimed by the Porter patent) has been shown to be capable of rendering 9   Samuel J. Porter, ''Method of Desensitizing Fertilizer Grade Ammonium Nitrate and the Product Obtained," U.S. patent number 3,366,468.

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors fertilizer-grade AN nondetonable under all circumstances when the additive is present in concentrations of about 20 percent or less. The present state of knowledge identifies neither the additive nor the critical levels of inertant needed to guarantee nondetonability. High concentrations of inertants may not be practicable, because of both their cost and their deleterious effect on the utility of the fertilizer. At present, there is no widely accepted standardized test protocol for determining whether a substance would be detonable under conditions likely to exist in large-scale bombings. A small quantity of an improvised explosive may not detonate, whereas a large quantity may make a very effective bomb. Thus, any suitable test of detonability must be experimentally validated to confirm that it correctly predicts the detonability of car-or truck-bomb quantities of known terrorist explosive formulations. To date, methods proposed for inerting ammonium nitrate fertilizers have not received a thorough agronomic or economic analysis. Factors that should be examined include compatibility of any proposed inerting material with all crops grown in soil fertilized with bulk AN; any disruption of AN manufacturing and distribution processes caused by any proposed inerting material; cost increases to the end user caused by introducing any proposed inerting material; and potential environmental impacts of any proposed inerting material. Although explosive-grade ammonium nitrate is sometimes sold in the fertilizer market, there is insufficient justification to recommend regulations prohibiting this practice. Occasional sale of explosive-grade AN in the fertilizer market has raised some concerns about its availability to potential bombers. However, simple techniques are available that transform fertilizer-grade AN into a bomb ingredient as effective as explosive-grade AN. Thus, there would be little public safety benefit in requiring that markets for explosive-and fertilizer-grade AN be kept separate. Recommendations No requirements for inerting bulk ammonium nitrate used as a fertilizer are recommended at the present time. No practical method of inerting AN ha yet been found. Should the bombing threat escalate, inerting schemes not available today, but that might be developed in the future, could be considered. Standard test protocols for evaluating the detonability of bulk ammonium nitrate-based fertilizers should be developed by the federal government. Appendix H describes a test protocol presented for illustrative purposes. Many

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors laboratories in the United States are capable of running such tests, including those listed in Appendix I. Research to identify, explore, and demonstrate practical methods of inerting ammonium nitrate used as a fertilizer should be undertaken . Current fundamental understanding of explosive reaction mechanisms is inadequate to guide research for inerting fertilizers. Both fundamental and applied research programs should be defined and funded to develop new inerting methods that could be ready for implementation if the bombing threat escalates. Packaged ammonium nitrate-based fertilizers typically sold in retail outlets should be sold only as nondetonable mixtures (as defined by a standard test protocol developed in response to Recommendation 9). Alternatively, the purchaser should be required to produce identification and the seller to keep records of the transaction. This recommendation is intended to prevent the undocumented retail purchase of pure AN, which might be used in illegal bombings. The economic impact and agricultural suitability of proposed inerting methods should be thoroughly analyzed before requiring their application to bulk ammonium nitrate. The vast size, complexity, and societal significance of the agricultural sector of the U.S. economy require that caution be exercised when changes are considered. LIMITING CRIMINAL ACCESS TO EXPLOSIVES AND PRECURSOR CHEMICALS In addition to the technical approaches considered by the committee for controlling the illegal use of explosives in the United States, regulatory initiatives might also be valuable. Enactment in Switzerland of the 1977 Federal Law on Explosive Materials and the 1980 Federal Act on Explosives for Civil Purposes, and subsequent implementation of a uniform set of federal regulations,10 coincide with a decrease in bombings there.11 However, the number of factors that may have contributed to this decline is too large to enable unambiguous identification of its principal cause. Because a precursor chemical is essentially any chemical from which an explosive material can be improvised, the committee examined a range of common 10    The regulations governing use of explosives are specified in the order Concerning Explosive Materials issued March 26, 1980, by the Swiss Federal Council. 11    Communications from Swiss authorities during committee members' site visit, April 7-9, 1997 (see Appendix F).

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors chemicals that could cause an explosion and evaluated the utility to law enforcement of imposing increased controls on them. It found that there would be no substantial benefit to law enforcement if only precursors were regulated without also imposing adequate controls on the ultimate end products—the explosives themselves. The committee summarized on a "short list" a number of precursor chemicals and explosive materials that appear to pose the greatest risk. Because ammonium nitrate is the material most likely to be used in highly destructive bombings, it has the highest priority for control despite the extreme complexity of its distribution system in the United States and its singular importance for the mining, commercial explosives, and agricultural industries. Other chemicals of concern are sodium nitrate, potassium nitrate, nitromethane, concentrated nitric acid, concentrated hydrogen peroxide, sodium chlorate, potassium chlorate, and potassium perchlorate. For the chemicals on this short list, the committee recommends controls at three bombing threat levels: the current threat, an increased threat, and a greatly increased threat. At today's threat level, current practices are adequate for selling and controlling access to most of the short-list chemicals, but for some materials and market segments the committee recommends significant increases in controls. Conclusions Compared with some countries, the United States has relatively lax federal controls on the purchase of explosives. Although some states do have strict purchasing requirements, many states allow individuals to purchase explosives without background checks or adequate verification of their identity. Many high explosives used in bombings are stolen. Common targets of theft are believed to be small end users, many of whom may not have the legally required magazines for storing high explosives securely. Explosives stolen from these end users are available to bombers for use as detonators, boosters, or as the main charge in improvised bombs. Effective bombs can be synthesized from a variety of readily available chemical precursors. Those chemical precursors that pose the greatest threat in the United States were identified by the committee according to the following criteria: The chemical is available in substantial quantities (e.g., on the order of 100 pounds or more); The chemical is an essential component of an explosive system in significant

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors use or with the potential for significant use, where significant use is defined in terms of deaths, injuries, and property damage; and The chemical is a critical precursor, i.e., one not easily replaced in generating an explosive system. It is not feasible to control all possible chemical precursors to explosives. Efforts to control access should focus on the chemicals identified by the committee as current candidates for control in the United States. These chemicals are ammonium nitrate, sodium nitrate, potassium nitrate, nitromethane, concentrated nitric acid, concentrated hydrogen peroxide, sodium chlorate, potassium chlorate, and potassium perchlorate. Urea and acetone also meet the criteria for control but are adequately controlled if access to nitric acid and hydrogen peroxide is limited. This list of chemicals may change over time if the materials preferred for bomb making change. Incremental increases in controls on a few carefully selected precursor chemicals can help keep these chemicals out of the hands of bombers. Sales of bulk chemicals may be controlled at a level different from that applied to retail sales. Many models exist for controlling access to explosive precursor chemicals . Perhaps the most relevant are the regulatory controls placed on chemicals used in the synthesis of illegal drugs. Also, the voluntary "Be Aware for America" program12 established by the fertilizer industry to keep ammonium nitrate and other explosive fertilizer chemicals out of the hands of bombers appears to be a positive step, but it must be improved by more rigorous implementation and stronger interaction with law enforcement. Recommendations Criminal access to explosives in the United States should be made more difficult by the following legislative actions: Creating uniform national regulations for the purchase of commercial high explosives. At a minimum, these regulations would extend current interstate controls (i.e., federal requirements for licensing and verification of compliance with storage requirements) to cover intrastate explosives transactions; and 12    The program and publicity materials were developed collaboratively in 1995 and are described in a brochure, "Be Aware for America: 1995," developed by the Fertilizer Institute; the Bureau of Alcohol, Tobacco, and Firearms; the Association of American Plant Food Officials; and the Agricultural Retailers Association.

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors Giving the Bureau of Alcohol, Tobacco, and Firearms the authority and resources to ensure that all purchasers of high explosives use secure magazines if the explosives are to be stored. The options below should be considered for controlling criminal access to the precursor chemicals listed by the committee: ammonium nitrate, sodium nitrate, potassium nitrate, nitromethane, concentrated nitric acid, concentrated hydrogen peroxide, sodium chlorate, potassium chlorate, and potassium perchlorate. The most appropriate option for control depends on the perceived level of threat. Options for consideration include the following: Establishing voluntary industry controls on sales similar to the "Be Aware for America" program; Requiring that purchasers show identification and sellers keep records of transactions; Requiring that sellers have licenses and that purchasers obtain permits; Making the listed chemicals nondetonable by addition of certain additives; and Banning sales of listed chemicals in certain markets. At the current level of threat, the committee recommends the following: The "Be Aware for America" program for sales of bulk nitrate fertilizers should be strengthened by more rigorous implementation and by establishing partnerships with local and national law enforcement agencies. Packaged ammonium nitrate-based fertilizers typically sold in retail outlets should be sold only as nondetonable mixtures (as defined by a standard test protocol developed in response to Recommendation 9). Alternatively, the purchaser should be required to produce identification and the seller to keep records of the transaction. Additional controls should not be placed on sales of any other precursor chemical at the present threat level. At an increased threat level, the committee recommends the following additional controls: Purchasers of bulk nitrate-based fertilizers and large quantities of sodium nitrate, potassium nitrate, nitromethane, concentrated nitric acid, concentrated hydrogen peroxide, sodium chlorate, potassium chlorate, and potassium perchlorate should be required to produce positive identification. Sellers should be required to keep records of sales transactions for a specified period of time.

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors At greatly increased levels of threat, the committee recommends the following additional controls: Sellers of bulk detonable nitrate fertilizers should be required to have licenses, and purchasers should be required to obtain permits. Packaged ammonium nitrate-based fertilizers typically sold in retail outlets should be sold only as nondetonable mixtures (as defined by a standard test protocol developed in response to Recommendation 9). Alternatively, sellers should be required to have licenses and purchasers should be required to obtain permits. Sellers of sodium nitrate, potassium nitrate, nitromethane, packaged concentrated nitric acid, concentrated hydrogen peroxide, sodium chlorate, potassium chlorate, and potassium perchlorate should be required to have licenses and purchasers should be required to obtain permits. Alternatively, sales of these chemicals in some markets should be banned. The list of chemical precursors to be controlled should be reevaluated periodically to correlate with ongoing assessment of the level of threat posed by illegal use of explosives. Bombers have demonstrated that they can change their tactics in response to the implementation of controls or shifts in the availability of particular chemicals or precursors. INTEGRATED APPROACH TO IMPLEMENTING RECOMMENDED OPTIONS FOR ACTION To facilitate development of a flexible national strategy to contain the threat from illegal bombing, the committee's recommendations can be used as steps in a strategy of progressive controls and measures based on policymakers' ongoing assessment of the bombing threat level. These progressively stringent measures would likely be regarded by the terrorist or criminal as increasingly severe obstacles to the illegal use of either commercial or improvised explosives for large-scale destruction. Although complying with regulations or any changes to the efficient status quo could be quite costly for industry, agriculture, and the consumer, the price paid in lives lost, property damage, and the diminished security of U.S. citizens as a result of uncontrolled large-scale bombings of public facilities could potentially be enormous. A determination of when to accelerate from controls at the current level of threat to those appropriate for increased or greatly increased threat levels would be made by U.S. government policymakers.

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors Current Threat The actions recommended at the current level of threat reflect current technological capability, ease of implementation, predicted value, and predicted cost. They include the following: Implementing International Civil Aviation Organization (ICAO) vapor marking of plastic and sheet explosives; Conducting preemptive research on (1) new techniques to detect unmarked explosives, (2) use of ICAO (or similar) chemical vapor marking of some commercial explosives, (3) a coincident gamma-ray marking prototype, (4) a practical identification taggant system, and (5) practical fertilizer-grade AN inerting methods; Increasing deployment of explosives detectors to critical sectors beyond airports; Developing standard test protocols to evaluate the detonability of bulk AN-based fertilizers; Prohibiting sales of packaged, detonable AN-based fertilizers unless purchaser identification and accurate record keeping for sales are required; Adopting uniform national standards for the purchase of commercial explosives and increasing enforcement of existing storage and security regulations; and Strengthening the "Be Aware for America" program as it applies to sales of bulk nitrate fertilizers. Increased Threat Additional options for action recommended to combat an increased level of threat from illegal bombings are those for which necessary technical capabilities are currently lacking or for which the costs at present are unwarranted, the inconvenience of implementation is too great, or the utility is too limited. Additional actions recommended at an increased level of threat are as follows: Expanding implementation of ICAO (or similar) vapor marking to some commercial explosives, if technically feasible; Implementing identification tagging of packaged, cap-sensitive explosives and/or initiators, providing that the taggants satisfy appropriate technical criteria; and Requiring purchaser identification and record keeping for bulk sales of nitrate-based fertilizers and for large purchases of sodium nitrate, potassium nitrate, nitromethane, concentrated nitric acid, concentrated hydrogen peroxide, sodium chlorate, potassium chlorate, and potassium perchlorate. The list of chemical precursors to be controlled would have to be reevaluated periodically.

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Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors Greatly Increased Threat At a greatly increased level of threat, the recommended actions are those for which necessary technical capabilities are currently lacking or for which the costs at present are unwarranted, the inconvenience of implementation is too great, or the utility and applicability are too limited. Additional actions recommended at a greatly increased level of threat are as follows: Considering the use of coincident gamma-ray marking of detonators and/or explosives; Implementing an inerting technique for bulk fertilizer-grade ammonium nitrate if technically feasible, agriculturally suitable, and economically acceptable methods are found as a result of future research and development efforts; and Requiring licenses for sellers and permits for purchasers of bulk and packaged detonable nitrate-based fertilizers, sodium nitrate, potassium nitrate, nitromethane, concentrated nitric acid, concentrated hydrogen peroxide, sodium chlorate, potassium chlorate, and potassium perchlorate. The alternative would be to ban sales of specific precursor chemicals in certain markets.