As engineers move into the somewhat new field of assessing vulnerability to terrorist threats, they need to understand the tools available to them and the associated limitations. To facilitate this understanding, an overview of the basic categories of prediction methods for airblast loadings from bomb detonations is presented. The complex problem of bomb detonation beneath an overpass bridge--an area that is semi-enclosed and where numerous reflecting surfaces exist--is used to aid the discussion and to highlight the importance of using the appropriate prediction methods and tools to address problems. Results from three prediction methods are compared. The high-fidelity Second-Order Hydrodynamic Automatic Mesh Refinement Code appears to be superior to the Conventional Weapon Effects Predictions and BlastX codes in terms of accuracy for use in complex environments such as that beneath a bridge, but the complexity, cost, and time required for use of this method make it prohibitive in most cases. The use of more economical and less accurate methods may suffice as long as their limitations are understood and appropriately accounted for in the analytical process.