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IED precursorsAOAV's IED researchAOAV: all our reportsImprovised Explosive Devices

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

Chapter 5: Analysis

Positioning ourselves within the perpetrator’s decision matrix is paramount. It allows us space for our manoeuvre. A large amount of academic work has been completed on precursor control, which certainly provides boundaries for those chemicals of significant concern. There appears to be general agreement that certain precursors require restriction, substitution, standardization and policing – but a global policy, which draws on best practice, appears lacking.

Annex F compares the international, regional and national approaches with Table 1. It is observed from the areas shaded red that views on chemical importance vary (perhaps linked to national threat analysis) and that disagreement (in the detail) surrounds standardized limits for % compositions in solid mixtures or % compositions in aqueous solutions.

The EU considers AN where the nitrogen content is >16% by weight problematic. Australia, Canada and Singapore cite 45 and 60%. Hydrogen peroxide is similar (varies between 12 and 65%), yet it is the aqueous precursor to OPE and hydrogen peroxide / organic material (HPOM) composition.

Observations: when hydrogen peroxide at concentration 60% w/w is mixed with glycerine, ethylene glycol, methanol, or organic fuel substances (such as flour, sugar, coffee and pepper) it forms a highly effective explosive (21 July 2005, the 7/21 bombing of a London bus incorporated a HPOM mixture). When AN > 28% is mixed with an organic fuel it becomes detonable. As such the variation in limit range allows viable HME compositions to be made, and the higher the limit range the less complicated is the chemistry to enhance it. Incoherent standardization also causes unnecessary confusion with legitimate commerce and international trade.

With that in mind, the ‘remarks’ column in Annex F provides an explosive engineering perspective on the importance of each precursor in HME manufacture and why consideration should (or should not) be given to its restriction, substitution or standardization within a global legislation. It is also useful to remember that precursors can be obtained in national retail outlets and this is where the principal issue of substitution needs to be considered. Sodium azide has already been mentioned above, but an ammonium nitrate-based coolpack is also a useful example. The ammonium nitrate within the coolpack is exploitable and could easily be replaced by a non-precursor salt that is sufficiently endothermic. And whilst these examples are relatively straightforward, other substitutions may not be obvious and require funded research to identify them. Given the costs of research, development and implementation, there also needs to be clear incentives from the market or elsewhere to initiate the process.

Recommendations: The disparity in national and regional legislation regarding precursor chemicals suggests that restriction, substitution and standardization would be better served within a global response to the violence carried out using precursor chemicals and with the draft of more uniform legislations at the international level. A system approach to research in this field should be funded, internationally, to search for viable substitutes within the marketplace.


An array of improvised explosive devices containing ammonium nitrate (AN) and aluminium explosive. BCL-RO.

Chapter 6:Future Trends

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