Improvised explosive devices (IEDs) are a type of unconventional explosive weapon that can be deployed in a variety of ways, and can cause loss of life, injury, and property damage in both military and civilian environments. Terrorists, violent extremists, and criminals (collectively referred to in this report as malicious actors) often choose IEDs because the ingredients, components, and instructions required to make IEDs are highly accessible. In many cases, precursor chemicals are used to make homemade explosives (HMEs), which are often a component of IEDs. HMEs are defined in this study as explosives produced from precursor chemicals either physically blended or combined in a chemical reaction. Many precursor chemicals are frequently used in industrial manufacturing and may be available for commercial or personal use. Guides for making HMEs and instructions for constructing IEDs are widely available and can be easily found on the internet.
Other countries restrict access to precursor chemicals in an effort to reduce the opportunity for HMEs to be used in IEDs. Although IED attacks have been less frequent in the United States than in other countries, IEDs remain a persistent domestic threat. Restricting access to precursor chemicals might contribute to reducing the threat of IED attacks and in turn prevent potentially devastating bombings, save lives, and reduce financial impacts.
In 1998, the National Research Council published a study titled Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing Explosives and Their Precursors, which was responsive to a congressional mandate to the Department of the Treasury in the Antiterrorism and Effective Death Penalty Act of 1996. That study, conducted in the aftermath of the World Trade Center and Oklahoma City bombings,
focused on precursor chemicals used primarily to produce HMEs for the main charges in large-scale IEDs, consistent with those attacks. It developed a short list of precursor chemicals of greatest concern in that context and made recommendations for limiting and controlling their availability for illegal use. The results of the study were incorporated in a Department of Homeland Security (DHS) rulemaking on Chemical Facility Anti-Terrorism Standards in 2007. In large part, high-profile terrorist incidents like the Oklahoma City bombing also motivated previous efforts to regulate precursor chemicals in the United States, leading policy makers to focus on ammonium nitrate, one of the precursor chemicals used in that incident.
Twenty years later, the threat of IEDs has evolved. Much of the transformation can be attributed to an internet-enabled increase in the availability of mat-rials and know-how, and to differences in other aspects of the threat environment related to actors, motives, and methods.
At the request of DHS, the Academies assembled a committee of experts in chemistry, energetic materials, supply chain management, economics, illicit markets, defense, law, and other fields to prioritize precursor chemicals that can be used to make HMEs; analyze the movement of those chemicals through United States commercial supply chains and identify potential vulnerabilities; examine current United States and international regulation of the chemicals; and compare the economic, security, and other tradeoffs among potential control strategies.
STUDY APPROACH AND CONCLUSIONS
During the course of its deliberations, the committee heard from experts and stakeholders from government agencies, industry (including trade associations), and academia. Experts and stakeholders presented or provided data on the movement of specific chemicals through the supply chain and on related policy mechanisms directly to the committee during one of several data-gathering meetings and in follow-up communications. Additionally, the committee chair, a committee member, and a staff officer conducted a site visit in April 2017 to the European Commission in Brussels, Belgium, and to the United Kingdom’s Home Office in London, England, to learn more about international policy on precursor chemicals and potential control strategies. The committee also sourced references from public documents, including the scientific literature and government reports, but did not use controlled or classified materials to construct any aspect of this report. The committee’s overall approach is described in greater detail in Chapter 1.
In responding to the statement of task, the committee focused solely on precursor chemicals used to make HMEs. The committee recognizes, however, that the majority of bombing incidents in the United States involve certain explosives—smokeless powder, black powder, flash powder, and pyrotechnic fillers—likely due to their ease of legitimate acquisition. Thus, no strategy for
restricting access to precursor chemicals can eliminate the threat of IED attacks as long as these other explosive materials remain accessible.
A wide range of precursor chemicals can be used to make HMEs. To assess the Precursor Chemicals Used to Make Homemade Explosives (Chapter 2), the committee assembled a chronological list of incidents that involved explosives, beginning nearly 50 years ago with the first major domestic incident that employed HMEs, which occurred in Sterling Hall at the University of Wisconsin. The data show that large-scale devices, such as the vehicle-borne IEDs (VBIEDS) used in the World Trade Center and Oklahoma City bombings, and smaller-scale devices, such as the person-borne IEDs (PBIEDs) employed more recently in Boston, New York, and New Jersey, pose a significant risk, even if all did not employ HMEs. Past research and regulatory efforts have tended to focus on the threat posed by VBIEDs, but attacks that employ PBIEDs can have and have had serious consequences both domestically and internationally (see Chapter 2).
This study, in contrast to past studies, focused on precursor chemicals that can be used as main charges in VBIEDs or PBIEDs. However, the committee did not assess precursor chemicals that are used only in very small amounts, as in the manufacture of aviation IEDs or detonators, or certain ubiquitous chemicals, such as food products, which would be too difficult to control.
The committee developed a prioritized list of precursor chemicals according to three criteria: (1) whether the precursor chemical could be used in both VBIEDs and PBIEDs, (2) whether the precursor chemical had a history of use in IED attacks, and (3) whether the precursor chemical could be used to make HMEs, independent of the presence of another specific chemical. On that basis, the committee established three groups of precursor chemicals—Groups A, B, and C—by order of priority (see Table S-1). With one exception, it placed chemicals that satisfied all three criteria in Group A, indicating the highest current priority. It placed chemicals that satisfied two of the three criteria in Group B; and it placed chemicals that satisfied one of the three criteria in Group C. The precursor chemicals in Groups B and C do not pose the greatest threat at the time of this report, but could gain greater prominence in the future given the potential for changes in the threat environment and use of the precursor chemicals in HMEs. Because the threat of IED attacks continues to evolve, the committee stresses the importance of reevaluating the groupings to address shifting tactics and precursor chemical use.
The committee next examined the Domestic Chemical Supply Chains (Chapter 3) of Group A precursor chemicals, the security mechanisms in place along the supply chains, and potential vulnerabilities that terrorists might exploit to access precursor chemicals. Precursor chemicals enter the supply chain as imports or through manufacturing; are transported and stored; arrive at retail locations; and exit via export or sale to consumers or to agricultural or industrial end users. Numerous federal agencies (including DHS, DOJ, DOT, EPA, and OSHA), state agencies, and voluntary programs, like ResponsibleCare and
|Charge Size||Prior Use||Dependency|
|Group A||Aluminum (powder, paste, flake)||V/P||Y||1|
|Calcium ammonium nitrate||V/P||Y||1|
|Urea ammonium nitrate solution||V/P||N*||1|
|Group B||Calcium nitrate||V/P||N||1|
|Group C||Ammonium perchlorate||P||N||1|
NOTE: *See discussion in Chapter 2 for explanation of including UAN in Group A. V: VBIED (~40 lbs to 10,000 lbs), P: PBIED (~1 lb to 40 lb), Y: used historically, N: not used historically, I: independent, D: dependent.
ResponsibleAg, managed by private organizations contribute to restricting access to precursor chemicals, but they do so differently, resulting in inconsistencies and gaps in oversight. Nevertheless, industry tracks movement of precursor chemicals, especially in bulk quantities, through much of the supply chain, and security mechanisms are in place at many of the early nodes in the chain, starting with imports and manufacturing.
By contrast, the available data suggest that a malicious actor can easily acquire enough precursor chemicals to manufacture a HME through legal purchases at retail outlets, especially outside of agriculture. The precursor chemicals sold at retail outlets have legitimate uses and often fall below the quantity thresholds mandated by existing regulations, and are therefore subject to little or no oversight as a security matter.
The committee concluded that retail-level sales present a substantial vulnerability in the supply chains under consideration. Retailers, especially those selling through internet commerce, have not been a major focus of federal regulation or of voluntary programs, except in a limited number of specific circumstances and sectors, such as agriculture. Internet commerce presents additional challenges because of the anonymity of purchasers, the ease of sharing information, and the large volume of transactions that occur online. All Group A precursor chemicals that can be purchased online can be delivered to a home or business address with very few restrictions.
Presently, binary exploding target kits present one of the most accessible and readily usable forms of precursor chemicals. These kits contain precursor chemicals in the proper weights and physical forms—and with instructions for use—to create an optimized HME that does not require either a commercial detonator or any other primary explosive to detonate. Moreover, exploding target kits are widely available through online and brick-and-mortar retailers.
The committee looked at International Regulations (Chapter 4), specifically the regulations in place to restrict access to precursor chemicals in Australia, Canada, Singapore, the United Kingdom, and the European Union (EU) overall, for insight into possible control strategies. The regulators in those locations have tended to focus on point-of-sale restrictions and have accumulated enough experience to provide some information on the strengths and weaknesses of different approaches to restricting access, even if the applicability to the United States’ policy environment is imperfect. Although the benefits of security regulations are difficult to track (Appendix G), authorities in the EU believe their restrictions on access, which have included retail bans, licensing, and registries, have reduced the threat of attacks using IEDs made with HME precursor chemicals, albeit at some cost to commerce. They frame threat reduction as the decrease in the amount of explosives precursors on the market and the increase in capacity for law enforcement authorities to investigate suspicious incidents involving explosives precursors.
Using the lessons learned from international regulations, the committee began Assessing Possible Control Strategies (Chapter 5) that could include
different combinations of mandatory and voluntary policy mechanisms, directed at retail sales to noncommercial end users (i.e., the general public). The committee considered tradeoffs among security, economic, and other factors associated with a small set of possible strategies, drawing notionally from principles of regulatory assessment (Appendix G), including those of benefit-cost analysis. It assessed the strategies qualitatively in relation to three goals: (1) restricting malicious actors’ access to precursor chemicals, (2) gathering and disseminating information to prevent or respond to terrorist incidents, and (3) minimizing the burdens on legitimate commerce and use. In deference to the third goal, the committee did not consider restrictions on access for commercial end users; in each case, a commercial purchaser, such as a housecleaning, pool, or spa service or a beautician, would only be expected to provide evidence of commercial status to complete a transaction.
The committee considered four general types of control strategy, each differing by the form of control, defined as a mandatory restriction on access to precursor chemicals. Three of the strategies would feature a new control, either a ban, licensing, or a registry; one of the strategies, referred to here as “business as usual plus,” would not feature a new control, but would augment any existing controls with supplemental measures and activities, such as outreach, training, and reporting. Indeed, any of the four strategies, not just business as usual plus, could incorporate such measure and activities. The committee notes that outreach, training, and reporting could be implemented as mandatory or voluntary programs, implying varying degrees of government and industry involvement and the potential for a hybrid strategy.
Overall, of the four types of control strategy considered, none emerged as a best choice during the committee’s deliberations on security, economic, and other tradeoffs. For example, the committee found the benefits of stringency might come at the price of forgone sales and use, displacement to other forms of terrorism, and commercial disruption. The committee lacked the time, resources, and directive from the U.S. Department of Homeland Security (DHS) to conduct a comprehensive and detailed analysis of policy options. Thus, this report constitutes a starting point, not an ending point for evaluating possible control strategies.
A full analysis, as would be necessary to support a policy decision, would require more time, data, industry participation, and specificity about the structure and content of proposed actions. Any such analysis should also consider the results of existing domestic programs that restrict access to precursor chemicals, including those intended to curb illicit drug production, and programs adopted in other countries. The EU’s continuing experience with bans, licensing, and registration might provide fertile ground for an analysis of those types of controls and lessons learned about what is, or is not, working in the EU, the related costs and unintended consequences, and the applicability to U.S. policy making.
Precursor chemicals have played a role in the manufacture of HMEs in prior IED terrorist attacks, and that role will continue to change with time as the threat environment evolves. Given the ease of accessing HME precursor chemicals and the information to manufacture IEDs, particularly via the internet, the threat of terrorist attacks using IEDs within the United States has not abated.
While the United States has not experienced an attack with a large-scale VBIED since the 1990s, the committee stresses the importance of deliberative thinking before crises, and cautions against intuitive thinking and action bias during and after crises. History suggests that a push for a policy response—from the public and government officials—often follows a crisis, but event-driven policy making, based on spontaneous, intuitive thinking, suffers limitations and can yield counterproductive results. The committee also stresses the importance of periodically reevaluating priorities among precursor chemicals, in light of changes in the threat environment, and of designing control strategies with means of harvesting and leveraging data to learn from experience and strengthen the strategies over time.
Pursuant to the primary goal of reducing the threat of IED attacks by restricting access to precursor chemicals, the committee details six recommended courses of action and four research areas meriting future attention in Chapter 6. The committee emphasizes the essential role of Congress in developing and implementing appropriate risk-reducing control strategies. Congress can be particularly instrumental in ensuring that crisis-driven interests do not unduly influence new laws or regulations, and can play a role in each of the six recommendations listed below to enhance the nation’s domestic and international risk-reduction programs.
Priority Precursor Chemicals
Recommendation 1: Federal, state, local, and private sector entities attempting to reduce the threat of IED attacks by restricting access to precursor chemicals should focus on both person-borne and vehicle-borne IEDs.
Recommendation 2: Federal, state, local, and private sector entities attempting to reduce the threats from person-borne and vehicle-borne IEDs should consider multi-chemical, rather than single-chemical, strategies.
Strategies at the Retail Level
Recommendation 3: Federal, state, local, and private sector entities attempting to reduce the threats from person-borne and vehicle-borne IEDs should focus on retail-level transactions of precursor chemicals, especially e-commerce.
Recommendation 4: Federal, state, local, and private-sector entities should explore strategies for harmonizing oversight of the sale and use of commercially
available kits that contain precursor chemicals that are specifically designed to be combined to produce homemade explosives.
Analysis of Control Strategies
Recommendation 5: U.S. DHS should engage in a more comprehensive, detailed, and rigorous analysis of specific provisions for proposed mandatory and voluntary policy mechanisms to restrict access to precursor chemicals by malicious actors.
Voluntary Measures, Activities, and Programs
Recommendation 6: The federal government should provide additional support for voluntary measures, activities, and programs that can contribute to restricting access by malicious actors to precursor chemicals used to manufacture IEDs.
In addition to the aforementioned recommendations, the committee identified several areas of research that could provide additional pathways for limiting access to precursor chemicals or designing appropriate regulations. Major topics for future research include the following:
- standardization of explosives incident data collection;
- substitution of precursor chemicals in commercial products;
- standardization of regulatory thresholds; and
- understanding behavioral responses, including those of terrorists, to proposed controls and those of policy makers to terrorist attacks.