Predicting explosive response to jet attach is difficult due to the complex nature of the projectile. The shock duration term in the critical energy (Ec) criterion developed by Walker and Wasley for plate impact is modified for application to round-nosed rods which appear to simulate jet attack. Experimental data on explosive initiation threshold in the cases of plate or rod impacts, LS DYNA2D simulations and data obtained with the new criterion are in good agreement.