Nov. 14, 2017


New Report Calls for Greater Oversight of Precursor Chemicals Sold At the Retail Level to Reduce Threats from Improvised Explosive Devices

WASHINGTON – Policymakers’ efforts to reduce threats from improvised explosive devices (IEDs) should include greater oversight of precursor chemicals sold at the retail level – especially over the Internet – that terrorists, violent extremists, or criminals use to make homemade explosives, says a new report from the National Academies of Sciences, Engineering, and Medicine.  While retail sales of these precursor chemicals present a substantial vulnerability, they have not been a major focus of federal regulations so far.

“The bombings of the Murrah Federal Building in Oklahoma City and the World Trade Center in New York City in the 1990s and those over the past few years in Paris, Brussels, and Manchester, in New York and New Jersey, and in many other communities around the world starkly demonstrate the long lived and persistent threat posed by IEDs,” said Victoria Greenfield, chair of the committee that wrote the report, and a visiting scholar in the department of criminology, law and society at George Mason University. “The report stresses the importance of engaging in an ongoing deliberative process to reduce this threat.”

The report, which was requested by the U.S. Department of Homeland Security, identifies, lists, and prioritizes precursor chemicals that can be used to make homemade explosives, using criteria on utility and use to separate them into Groups A, B, and C. The 10 chemicals in Group A constitute the greatest current threat and should be the highest priority for policymakers’ attention, the report says. 

Precursor chemicals enter the supply chain as imports or through manufacturing and make their way to industrial, agricultural, and other end users. Industry tracks the movement of chemicals through much of the supply chain, but visibility and oversight appear to diminish as chemicals approach the end of the line. Data suggest that a terrorist can acquire enough precursor chemicals to manufacture homemade explosives through legal purchases from retail outlets.  While the Oklahoma and New York City bombings employed thousands of pounds of precursor chemicals, many contemporary incidents have involved much smaller quantities that are readily available to consumers.

Conscious of the need to address this vulnerability yet minimize the burden on legitimate commerce, the committee assessed four general types of control strategy, directed at a subset of retail sales to noncommercial end-users, that is, the general public.  Each strategy could include different combinations of mandatory and voluntary policy mechanisms, but three would feature a new control—a ban, a licensing requirement, or a registry for non-commercial purchases—and one would augment existing controls with increases in related outreach, training, and reporting.

Of the four types of strategy, none emerged as the best choice during the committee’s deliberations on security, economic, and other trade-offs, the report says, noting that the committee lacked the time, resources, and directive from DHS to do an in-depth analysis of these policy options and that such an endeavor would require greater specificity about the terms of proposed actions.  The report calls on DHS to use the committee’s assessment as a starting point for engaging in a more comprehensive, detailed, and rigorous analysis of specific provisions for mandatory and voluntary policy mechanisms.

In examining possible policy options, policymakers and private-sector entities should consider strategies that would address multiple chemicals, rather than just a single chemical, the report says.  Historically, terrorists’ have modified their tactics by using alternative chemicals in response to single-chemical controls.  The federal government also should provide more support for voluntary measures and programs that can help restrict access.  Regardless of the path chosen, the report calls for re-evaluating priorities among chemicals and re-visiting policy responses regularly, in light of changing threats.

In addition, federal, state, local, and private-sector entities should explore strategies for harmonizing oversight of the sale and use of commercially available exploding target kits that are designed to produce homemade explosives, the report says. Some states have implemented rules independently, but no federal agency has explicit authority from Congress to oversee the sale of these kits. 

The committee also identified opportunities for future research, including work to identify chemicals that could replace precursor chemicals in commercial products and to better understand how terrorists might respond to possible controls.  

The study was funded by the U.S. Department of Homeland Security. The National Academies of Sciences, Engineering, and Medicine are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine.  The National Academies operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln.  For more information, visit

Riya V. Anandwala, Media Relations Officer
Joshua Blatt, Media Relations Assistant
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Copies of Reducing the Threat of Improvised Explosive Device Attacks by Restricting Access to Explosive Precursor Chemicals are available at or by calling 202-334-3313  or 1-800-624-6242. Reporters may obtain a copy from the Office of News and Public Information (contacts listed above).


Division on Earth and Life Studies
Board on Chemical Sciences and Technology
Committee on Reducing the Threat of Improvised Explosive Device Attacks by Restricting Access to Chemical Explosive Precursors


Victoria A. Greenfield (chair)
Visiting Scholar
Department of Criminology, Law, and Society
George Mason University
Fairfax, Va. 

Robert G. Best
Joint Improvised-Threat Defeat Organization
Defense Threat Reduction Agency
U.S. Department of Defense
Burke, Va.

Leo E. Bradley
Independent Consultant and Owner
LE Bradley Consulting LLC
Alexandria, Va.

John C. Brulia
Director of Safety and Compliance (retired)
Austin Powder Co.
Sagamore Hills, Ohio

Carrie L. Castille
Agriculture and Natural Resources Consultant
Breaux Bridge, La.

David G. Delaney
Senior Fellow
Center for Health and Homeland Security
University of Maryland

Arthur G. Fraas
Visiting Fellow
Resources for the Future
Chevy Chase, Md.

William J. Hurley
Adjunct Research Staff Member
Joint Advanced Warfighting Division
Institute for Defense Analyses
Alexandria, Va.

Karmen N. Lappo
Principal Member
Sandia National Laboratories
Albuquerque, N.M.

Becky D. Olinger
Science Adviser
Office of Counter Terrorism and Counter Proliferation
National Nuclear Security Administration
Los Alamos, N.M.

Jimmie C. Oxley
Professor of Chemistry and Co-Director
Forensic Science Partnership
University of Rhode Island

Kevin F. Smith
President and CEO
Sustainable Supply Chain Consulting
Windermere, Fla.

Kirk Yeager
Senior Forensic Scientist
Federal Bureau of Investigation
Quantico, Va.



Camly Tran
Staff Officer