AOAV: all our reportsIED precursors

An examination of the precursor chemicals used in the manufacture of explosive compositions found within Improvised Explosive Devices (IEDs)

Chapter 2: History

The following section will briefly introduce some recent historical events that have had a large effect on the use of precursor chemical materials in HME and IED construction. A broader historical overview of IED developments and usage over the centuries is available in AOAV’s report “Improvised explosive devices: past, present and future”. [2]


The Provisional Irish Republican Army (PIRA) bombing campaign (circa 1970) strongly influenced later HME usage in IEDs. Access to commercial explosives had been tightened up and large quantities became impossible to obtain. To sustain its primary tactic of widespread bombings, PIRA was forced to develop a range of HME based on precursor chemicals including potassium chlorate (PC), ammonium nitrate (AN), nitrobenzene, fuel oil, aluminium powder and sugar. These proved to be very capable explosive compounds that could be easily manufactured from widely available materials, concepts that were subsequently shared with European and Middle Eastern terror organisations, and which adapted quickly as controls against their use were implemented.


HME first appeared in large quantities in the United States (US) in 1970 when Vietnam protestors initiated a 900 kg device comprising AN and fuel oil (ANFO)

at the University of Wisconsin, Madison Campus. It caused USD $13M damage in 2020 dollars. The next significant attack in the US occurred when Timothy McVeigh and Terry Nicholls manufactured and deto- nated an IED at the Alfred P Murrah Federal Building in Oklahoma on 19th April 1995. Similar to Wisconsin, this device utilized ANFO, but also nitromethane and a commercial explosive booster. The device was estimated to contain over 2,300kg of explosive [3], cost 168 lives, and caused USD $510M damage.


The problem in using AN-based HME was that it required a booster of more powerful commercial/ military explosives (or very sensitive HME) to get it going. Powerful military detonators were insufficient. The ‘terrorist spring’ in the 1970s also saw specific legislation and more effective controls and security over the use and manufacture of commercial explosives in most developed countries. The lack of access to ‘booster quality’ explosives forced the majority of newly emerging terror groups, particularly in the Middle East, to examine other chemical compounds. The primary solution to initiation problems evolved in the form of organic peroxide- based explosives (OPE), using hydrogen peroxide as the principal oxidizer. OPE enjoyed being shock sensitive without the requirement of boosters and unlike AN-based HME, could be manufactured in liquid or gel form, thereby improving versatility.

The Alfred P. Murrah Federal Building in Oklahoma City, April 19, 1995, bombed using HME. By usacetulsa (CC BY 2.0).

Chapter 3:Precursor use in IED Manufacture

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