I would propose to use a dynamic loading factor (DLF). The DLF is a multiplier applied to the peak pressure in a static analysis to approximate the transient effects of the explosion. The DLF is calculated from the natural frequency of the structure and the blast load time and shape of the pulse. A reference I found useful for DLF calculation is:
Biggs, J.M., Introduction to Structural Dynamics. 1964: McGraw Hill.