A series of numerical simulations of rock blasting has been conducted using the LSDYNA software in order to test the hypothesis proposed by Rossmanith, stating that interaction of stress waves could result in finer fragmentation by controlling the initiation times. The rock material was simulated with the RHT material model. After the calculation, the elements with damage level above 0.6 were removed to simulate complete fracturing of the rock.Firstly, a series of numerical simulations were conducted to model the small-scale tests performed by Johnasson et al. (2013). This work also involved simulating initial damage to the rock through previous blasting, and analyzing the resulting effects. The effect of different delay times showed that through a properly chosen delay time, improved fragmentation could be inferred. Moreover, the initial damage (from the previous row) clearly affected the fragmentation; however, the results indicated that longer delay times (in which the stress wave would have passed the boreholes) also resulted in improved fragmentation, implying that stress wave superposition may not be the primary factor governing the fragmentation. Secondly, full-scale tests conducted at the Aitik open pit mine were modeled. The simulation results indicated that the case of no interacting stress waves (6 ms delay) gavefiner fragmentation at most of the interpretation section cuts compared to the cases of interacting stress waves (0, 1 and 3 ms delay times). Both the simulation results of small scale tests and full scale tests indicate that the stress wave interaction effect due to delayed initiation can result in finer fragmentation compared to simultanious initiation. However, the results also indicate that relatively long delay times, leading to no stress wave superposition, induce even finer fragmentation compared to the use of very short delay times.