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

Chapter 6:Future Trends

While we plan our strategy, so does the perpetrator. As their hand is forced to pursue other explosive effects, what does predictive threat analysis suggest? Two examples are provided.

Example 1. The perfection of a fuel air explosion, which differs from that created by a conventional explosive in that the fuel elements do not carry their own oxygen. For an explosion to occur, fuel must be mixed with ambient atmospheric air, and when mixing is complete, be initiated by a delayed ignition source. Delayed ignition is required in order that the fuel can mix appropriately with the air. Fuels involved take the form of gases, vapours, aerosolized liquids or particulate dust clouds, which all have varied upper and lower explosion limits. The energy released in a fuel-air explosion greatly exceeds that of HMEs.

Fuel air explosions have been attempted by armed groups, terrorists and criminals with varying degrees of success / failure as follows:

  • the 1983 Beirut bombing, where butane and PETN were used;
  • the 1993 World Trade Centre bombing where a urea nitrate main charge (enhanced with aluminium, magnesium and iron oxide) sat surrounded by bottled hydrogen to enhance the fireball and afterburn of the solid metal particles;
  • 1994 Jerusalem, propane and detonating cord (PETN);
  • Columbine High School 1999, where propane bombs were planted in the school dining hall;
  • the Ghriba synagogue bombing in 2002, with propane cylinders, PETN and delay detonators;
  • Glasgow International Airport 2007, propane;
  • Time Square 2010, propane, gasoline and urea with underlying delay considered in the design; Brindisi school bombing 2012, propane;
  • Karrada bombing Baghdad, 2016 (ammonium nitrate and > 20% fine aluminium)
  • Notre Dame 2016, propane;
  • Rotterdam 2017, butane;
  • Melbourne 2018, propane.

Bombing of Karrada, Baghdad, 2016, killed at least 340 civilians and injured hundreds more. The IED used contained ammonium nitrate and > 20% fine aluminium. Image: AFP/Getty Images

It is not appropriate for this paper to expose the chemistry behind some reasons of failure, but trial and error with fuel-air explosives (FAE) and thermobaric mixtures should be anticipated. The concept of mixing a combustible gas, dust or metal cloud with air, then detonating it, is simplicity itself.

Example 2. ‘Over-the-counter’ materials. Is it possible to synthesize HME such as TATP without the use of liquid peroxides given the revised precursor legislations already discussed? The answer is yes. Commonly available ‘over- the-counter’ materials, specifically percarbonates and perborates, are available in large quantities in fabric stain removers such as Vanish Oxy- Action and Oxi-Clean. The threatening feature ofpercarbonates and perborates is that when dissolved in water or subjected to an acid, both compounds release hydrogen peroxide. In terms of Vanish Oxy-Action, its active ingredient is sodium percarbonate. The percarbonate is essentially a solid and stable form of hydrogen peroxide. It can easily be added to acetone and with the addition of acids to neutralise the base carbonate, produces excellent crystals of TATP, depending on acid strength and conditions. With the addition of hexamine and acetone, HMTD can also be produced.

Recommendations: As perborates and percarbonates have no specific legislation applied to them, more focus on the matter is required by legislators to reduce their destructive capability.

Chapter 7: Conclusion

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