In this paper, an analytical model for determining the iso-damage curves for framed monolithic glass panels subjected to blast loading is proposed. Two typical damage levels corresponding to different conditions in GSA/ISC are classified, namely (a) the glass crack limit and (b) glass fragments invading with a certain velocity. The nonlinear dynamic responses and failure modes of framed monolithic glass under different blast loadings are firstly analysed numerically. Then critical states of glass panel in both impulsive region and quasi-static region of the pressure-impulse (P-I) diagram are defined. Based on the energy balance approach, an analytical method is proposed for determining the pressure asymptote and the impulse asymptote of framed monolithic glass for different damage levels. The proposed method is verified through comparison with published experimental data and numerical results. The method can be applied for any framed monolithic glazing with different dimension and thickness and provides a practical approach for engineering design and hazard level estimation of framed monolithic glass against blast loading.