The decay coefficient b can be calculated through a non-linear fitting of an experimental pressure time curve over its positive phase. Besides the peak pressure, for design purposes an even more important parameter of the blast wave pulse is its impulse because it relates to the total force (per unit area) that is applied on a structure due to the blast. It is defined as the shaded area under the overpressure-time curve of Figure 1. The impulse is distinguished into positive is and negative is¯, according to the relevant phase of the blast wave time history. Equation (2) gives the expression in the case of the positive impulse,which is more significant than its negative counterpart in terms of building collapse prevention,