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Stemming Specifications in Blasting With Dynamite

Stemming involves the use of an inert material to confine the energy produced by an explosive during blasting. Stemming is a significant part of the blasting process, as it locks in the gases emitted from explosives such as dynamite, to maximize the energy utilized during fragmentation. Specific guidelines must be adhered to if stemming is to be fully effective.

  1. Blasting

    • During rock blasting, holes are drilled into rock and filled with explosives. Stemming material is inserted at the top part of the hole, and the material is detonated. Each detonation produces large volumes of gases due to rapid decomposition of the explosive. These gases are responsible for rock fracture.

    Dynamite

    • Dynamite is the most widely known, yet most expensive explosive used for blasting. It is a nitroglycerin-based explosive, with high energy, velocity and strength. Dynamite is available in several forms, including extra-gelatin, semi-gelatin, propagation-resistant, and desensitized for water-blasting. Due to its heat and shock sensitivity, dynamite should not be removed from its factory cartridge. The quantity used in each blast hole is determined by the manufacturer's instructions.

    Stemming Material Size

    • For maximum efficiency, the stemming material must lock firmly into the blast hole, to fill any voids that may allow gas to escape and to reduce flyrock amount. This is achieved by using angular material with a diameter of at least 0.05 times that of the hole, or approximately 3/8 inch, which is the standard set by the United States Corps of Engineers.

    Stemming Distance and Material Type

    • Under normal conditions, the distance between the stemming material and the explosive is recommended at roughly 20 times that of the blast-hole diameter. Lesser distances may result in gas leakage and violent air vibration, while greater distances may cause poor breakage. Common stemming materials include drill cuttings and crushed stone, although increased flyrock and inefficient blasting have been reported with drill cuttings.

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