Flashing detonation grenade which can be used for massive riots is the most effective non-lethal weapons, fragments generated by its explosion may cause fatal injuries to animate goal. To improve security of bomb blast, box testing experiments and high-speed photography were used to analyze quantity and quality of distribution of the fragments that affect the remaining targets, a fragment velocity decay equation was established to determine the safety of bomb blast radius, all these findings provide a theoretical basis for evaluation of non-lethal effects and flashing stun grenade design improvement.