Steel hollow section (SHS) tubular members have been widely used in the construction, infrastructure, onshore, offshore, mining, protective and security industries. Thus, strengthening of steel hollow tubular members is required to safely carry the dynamic loads to increase the security demands when the accidents, intentional impact, or explosive events occurred. In this paper, a finite element analysis tool, LS-DYNA is utilized to study the behaviors of (SHS) beam under a uniform transverse blast load. The explosive loads were sufficient in magnitude to cause plastic deformation of the cross-section (local deformation) and plastic flexural deformation of the overall member (global deformation). Different parameters were studied to investigate the effects of beam depth (H), beam width (B), support condition and axial load on the failure mode. The obtained displacement-time history from each simulation was recorded and compared. A numerical method for deriving pressure–impulse (P–I) diagrams for (SHS) beam, which subjected to transient loads are described in this paper, which can be applied in the preliminary design of protective structures to establish safe response limits based on the given blast-loading. The proposed model of (P–I) diagrams exhibited a good accuracy in predicting the pressure–impulse diagram to design the (SHS) beam under the extreme loads.