An approach was proposed for the assessment of the expected number and drag factor of fragments generated in the collapse of a vessel Clue to internal pressure. The analysis of a database reporting data oil more than 140 vessel fragmentation events allowed the identification of a limited number of fragment reference shapes. The correlation of fragment reference shapes to the vessel credible fragmentation patterns allowed the assessment of the expected number and reference shape of fragments generated. Starting from the fragment reference shapes identified, simplified functions for drag factor calculation were developed, based oil few geometrical parameters of the vessel undergoing the fragmentation event. The probabilistic models for the expected shape and number of fragments generated and the simplified drag factor functions developed may constitute all important input for the analysis of the possible fragment trajectories in the framework of missile hazard assessment. (C) 2008 Elsevier FIN. All rights reserved.