Abstract: Two prediction methods were established based on the penetration experiments and theoretic analysis to rationally determine the initial velocity of the fragments. The initial velocity prediction model based on the initial kinetic energy was established by the total explosion energy and energy transferred factor. The total energy for the physical explosion of compressed gas tank and runaway reaction explosion can be estimated by Baum equation， while overheated energy as total energy produced by overheated liquid in BLEVE is more rational. The energy probability density transferred factor was obtained by the existing data collected from experiments of Baum， Birk， industrial explosions and maximum entropy principle. The results show that the probabilistic density of energy transferred factor is gamma distribution. Using the presented method， the initial velocity for the quantitative assessment of the explosion fragments can be predicted effectively.

Key words: fragments in explosion, fragments initial velocity, BLEVE accident, maximum entropy principle, probabilistic density function, gamma distribution