Blasting in Mines A typical blast-hole is shown in the following image. The primary factor that affects almost every other aspect of the blast is the hole diameter, this determines how much explosive can be used for a given hole length. The amount of explosive per length of hole determines the radius around the hole that the rock can be effectively broken. This impacts both the Spacing and the Burden for a blast. Some key considerations in the image are the Stemming and the Powder Column. The Stemming is loose material, usually leftover cuttings from when the hole was drilled, it is used to cap the upper end of the hole and prevent the explosive gases from escaping out the top of the hole. Holes are drilled down to a predetermined length below the depth of rock that needs to be broken. This ensures enough explosive energy will be transferred to the rock at that level. This is called the Sub-Drill Length.