ABSTRACT
Two types of permitted detonators are commonly manufactured and approved for use in Indian underground coal mines. These include: (1) instantaneous electric detonators; and (2) delay electric detonators. Only seven series of delay detonators with delay nos. 0 to 6 having 25 ms difference in their nominal delay timings are approved in India. Permitted instantaneous electric detonators are generally used with permitted (ordinary) or P1 explosive and permitted (equivalent to sheathed) or P3 explosive. Permitted delay electric detonators can be used only with permitted (for solid blasting) or P5 explosives in India (Roy & Singh, 2011). Permitted detonators are designed to initiate multiple charges of permitted explosives with a single application of firing current in the blasting circuit. In the solid blasting method, a free face is created by blasting a few holes and then blasting the remaining holes into this opening in a single round using a suitable combination of delay detonators.
