By Kirk Yeager, PhD, Senior Forensic Scientist, FBI Laboratory, Quantico, Virginia
n February 22, 2010, terrorist Najibullah Zazi pled guilty to conspiring to use weapons of mass destruction, conspiring to commit murder in a foreign country, and providing material support to a foreign terrorist organization. During the run-up to his disrupted plot, Zazi purchased numerous commercial products that he was trained to transform into deadly explosives. Zazi’s attempt to manufacture and use improvised explosives (IEs)—those that can be readily produced from common consumer products or commercial chemicals—was far from an isolated event. Terrorist usage of IEs is on the rise worldwide. To protect the security of the country and ensure their own personal safety, law enforcement officers must have a basic understanding of this evolving threat.
The Chemistry of Explosives
To recognize warning signs and indicators of the potential presence of IE materials, a very basic understanding of chemistry is required. The chemistry of explosives is the most rudimentary of all chemistries; it is the chemistry of fire and of life. In both a fire and an explosive event, a fuel is combined with some source of oxygen, heat is added, and a reaction is started, which releases energy through a combustion process.
In a fire, a fuel produces energy by reacting with oxygen from the air. In an explosive reaction, identical chemistry occurs. However, with an explosive, the reaction happens so rapidly that there is no time for oxygen to be brought in from the air. The explosive has to supply its own oxygen. At the most basic level, an explosive is a material capable of undergoing combustion chemistry without a source of external oxygen.
There are a select number of chemicals, called oxidizers, which can release oxygen quickly enough when combined with a fuel to produce an explosion. The best known oxidizer may be ammonium nitrate (AN). AN gained notoriety following the bombing of the Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma, and it is utilized by terrorists to this day in Iraq and Afghanistan as a precursor for IE formulations. When this chemical source of oxygen is mixed with a fuel oil such as diesel, the explosive ammonium nitrate/fuel oil (ANFO) is produced. This material is capable of rapid combustion, releasing all of its energy in approximately 1/100,000th of a second with great force and violence.
There are two ways to combine fuels and oxidizers to make an explosive: blending and cooking. Blending is the simplest and most common form of explosive manufacture and takes the least amount of chemical skill. This process consists of the physical mixing together of fuels and oxidizers. The ANFO mentioned earlier is a simple physical blend of AN and diesel.
Cooking, a term borrowed from the narcotics enforcement community and the meth lab phenomenon, is more complicated. In cooking, chemicals that are mixed together react to form new compounds with explosive properties. Cooking requires significantly more chemistry skill, as materials have to be run through a series of processes, each fraught with unique hazards such as toxic fumes and the potential for chemical burns or sudden explosions. IEs produced from both blending and cooking are routinely encountered by law enforcement.
Resources to Identify the Threat
The FBI has produced the Improvised Explosive Threat Card, a bifold reference card that provides law enforcement with an overview of chemicals that can be used for explosive production. Copies of the card and a detailed bulletin describing its use can be obtained upon request from the FBI Bomb Data Center by emailing email@example.com. This information and many other resources on this subject are availablethrough the Law Enforcement Online (LEO) website. User applications for LEO can be found at http://www.leo.gov/usrApp.html.1
The first page of the Threat Card, shown in figure 1, details common oxidizers and the compounds that contain them to help law enforcement quickly reference these materials. The presence of oxidizers remains one of the primary red flags to be aware of as an indicator of potential IE production.
|Figure 1. IE Threat Oxidizers|
Figure 2 represents a cross section of fuels commonly encountered in IE production. A full list of potential fuels is too extensive to cover, but the rule of thumb is any fuel that can be burned for energy can be used as a potential IE fuel.
The first column in figure 2 (labeled hydrocarbons) consists of the most basic fuels—those that are often found in most households. Law enforcement must use common sense when encountering these materials. For example, sugar in a pantry is not, in most cases, cause for alarm. However, sugar found on a work bench next to a container of a known oxidizer is grounds for suspicion.
The card also details the more exotic fuels—those not commonly found in consumer products. If law enforcement officers encounter elemental or “hot” fuels, the incident should be referred to a bomb squad immediately. These materials can form sensitive and dangerous explosives, threatening the safety of officers and others in the vicinity.
Cooking produces a wide range of dangerous IE materials. Figure 3 shows some of the most common cooked explosives and the materials used in their creation. In many cases, perpetrators are caught when unforeseen accidents involving these materials alert authorities to their activities. The peroxide explosives in particular are both extremely popular with home experimentalists and hypersensitive. In some cases, the static built up from shuffling across the floor and creating a spark is enough energy to ignite them.
|Figure 3. Common Cooked Explosives|
Unfortunately, knowing the chemicals that can be used to either blend or cook IEs is only part of the picture. A single chemical can be found in a variety of consumer products. For example, hydrogen peroxide is used in cleaning products, pool treatments, hair dyes, water purification systems, and hydroponics. Acetone can be found in both hardware stores and drug stores. Sulfuric acid is in both car batteries and consumer drain openers, and the list goes on. The FBI has produced multiple publications outlining consumer chemicals that can be used to produce explosives.2 These can be obtained by contacting the FBI Bomb Data Center or by enrolling in LEO.
The U.S. Department of Justice in collaboration with the Technical Support Working Group assembled a booklet outlining the most prevalent IE materials, their properties, the chemicals needed to produce them, the commercial sources of precursor chemicals, and the equipment that is needed for blending and cooking IEs. This booklet, Indicators and Warnings for Homemade Explosives, is available for sale to law enforcement from the Government Printing Office at http://bookstore.gpo.gov/actions/GetPublication.do?stocknumber=008-001-00185-1.
Bombers’ use of IEs is not a new trend. The attack on the World Trade Center building in 1993 and the Oklahoma City bombing in 1995 stand as testaments to the effective use of IEs in the hands of terrorists. As new forms of Internet media such as YouTube continue to gain popularity, explosives recipes available to a new generation of curious experimentalists are on the rise. Over the past decade, the odds of law enforcement encountering these materials have increased substantially. Law enforcement needs to thoroughly understand the methods and materials used to create IEs in order to fully protect officers, first responders, and the public from this growing threat.
For more information on the FBI’s Bomb Data Center or to request a copy of the Improvised Explosive Threat Card, email firstname.lastname@example.org. Download an application for an LEO account at http://www.leo.gov/usrApp.html. Visit the FBI’s Resources for Law Enforcement page to access additional publications and resources targeted to the law enforcement community at http://www.fbi.gov/stats-services/law-enforcement. ■
1Kirk Yeager, “Improvised Explosive Threat Card,” FBI Bomb Data Center Investigators Bulletin 2006-4.
2Kirk Yeager, “Explosive Peroxides,” FBI Bomb Data Center Investigators Bulletin 2006-2; and FBI Bomb Data Center, “Improvised Explosive Precursors,” FBI Bomb Data Center Investigators Bulletin 2009-1.
Please cite as:
Kirk Yeager, "What Law Enforcement Needs to Know about Improvised Explosives," The Police Chief 78 (September 2011): 52–55.