The paper justifies the optimal delay time in non-synchronous fan blasting with the most optimal delay time between the holes being 15 ms. Experiments were conducted to assess the breaking conditions and seismic effects of face blasts in the underground conditions of the Rasvumchorrsky mine using the Iskra-T electronic initiating systems with delay times of 10, 15 and 20 ms. With the delay times of 10 and 15 ms there is no clear segregation of the blast stages and interference of compression waves, created by consecutively blasted charges, takes place, while their joint interaction leads to insignificant increase of the seismic effects on the mine workings. According to the results of ore drawing monitoring, the number of boulders with the above delay times did not exceed 10 pieces for the whole blasted volume for each round. With the delay time of 20 ms a clear segregation of the blast stages was obtained with the minimum number of 7 boulders per blast. In order to ensure acceptable rock mass fragmentation quality and reduce the seismic effect of blasting on the mine workings, as well as to preserve the pilot holes drilled, it is advisable to use reverse initiation with non-synchronized fan blasting with the delay time of 20 ms between the holes.