||To simulate accurately a pressure wave propagation problem, a fine mesh is required in order to capture peak pressures accurately. This may require a very large size problem with several millions of elements. To reduce CPU time and prevent high mesh distortion, a two-dimensional problem for blast ignition and pressure propagation is performed first on a fixed Eulerian mesh. When the pressure wave gets closer to the structure, a three dimensional ALE simulation follows, where the fluid mesh and structure mesh at the fluid structure interface are coincident. The three dimensional problem is performed after mapping history variables from the two-dimensional to the three dimensional mesh. In this paper an ALE multi-material formulation is used for both explosive and air materials, and a classical Lagrangian formulation for the structure. The method has been implemented successfully in LSDYNA code and validated with different applications. To validate the method, this technique is used for pressure wave propagation, due to explosive detonation, and its interaction with the structure. The numerical solution, in term of maximum displacement, is compared to experimental data performed at Aeronautical and Maritime Research Laboratory at DSTO, Australia. Good correlation has been observed between numerical results and experimental data.