Stemming is the inert material filled between the explosive charge and the collar of the blasthole to confine the explosion. Stemming confines the propagation of the explosion to the horizontal direction; therefore little explosive energy is lost through the tops of the blasthole. This maximizes blast efficiency, and also minimizes safety hazards associated with flyrock and limits noise nuisance. The stem height is determined by the blasthole diameter and compressive strength of the rock mass to be blasted.

The explosive charge height is the height (or length) of blasthole filled with explosive material. Generally speaking,

explosive charge height = blasthole height – stem height.

Figure: Stemming is important in confining the energy of the blast. Usually crushed spoil rock is used as the stemming.