What is the purpose of stemming in blasting operations?

Stemming is a crucial element in blasting operations, primarily serving to control fragmentation. When explosives are detonated in a borehole, stemming involves filling the upper part of the hole with an inert material, such as crushed stone or soil, after the explosive charge has been placed. This practice optimizes the expansion of the explosive gases by preventing them from venting upward, thereby allowing more of the energy to be directed toward breaking the rock.

By controlling how the explosive energy is released, stemming can significantly influence the size and distribution of rock fragments resulting from the blast. A well-stemmed blast results in desirable fragmentation, which can improve efficiency in subsequent loading and hauling operations, reduce the need for secondary blasting, and minimize the creation of oversized rock that would be more difficult to manage.

While stemming contributes to safety and can help minimize environmental impacts, its primary purpose is to directly influence the fragmentation and efficiency of the blasting process.