How must permissible explosives be stemmed to remain permissible?

The requirement for permissible explosives is that they must be stemmed with incombustible stemming material that is at least 24 inches long. This is crucial because proper stemming helps confine the explosive gases and enhances the efficiency of the blast while also ensuring safety. Using incombustible material mitigates the risk of ignition from the heat generated during detonation and decreases harmful effects such as fly rock, which can cause significant hazards.

Stemming that is less than 24 inches or of a combustible nature might not provide adequate confinement, potentially leading to dangerous outcomes during detonation. Therefore, utilizing incombustible stemming material of the specified length not only adheres to safety regulations but also ensures the permissible use of explosives in mining and construction environments.