Modelling improvised explosive device attacks in the West – Assessing the hazard

Improvised Explosive Devices (IEDs) continue to be a terrorist weapon of choice. With increasing pressures on the economies of Western nations, spending on counter-terrorism is subject to greater scrutiny. Homeland security agencies are no longer exempt from government fiscal due diligence, needing to justify how their spending achieves best value-for-money. Probabilistic Risk Assessment (PRA) is a valuable tool that can assist in this endeavour. This paper introduces a PRA model that characterises IED attacks in Western nations, and can be used to assess the risk reduction associated with IED attack countermeasures. When using the model with the START open-source terrorism database we identified that current IED attack countermeasures provide a risk reduction of at approximately 22%, and that terrorists using IEDs in Western nations cannot generally be considered adaptive, with the operational effectiveness of terrorists being approximately 7%.