Figure 6. Underground blasting sequence in M13: (a) center hole for relief; (b) line drill for extra relief; (c) two burn shots; (d) U round; (e) trim round; (f) roof scaling and floor blasting. Zoom in for hole detonation sequence. Underground blasting occurred from inside to outside. A somewhat similar blast design was used in M15. respect to the 4th bench. Figure 5-b and c show the drilling of the 6.5 in (16.5 cm) burn hole drilled from outside to the inside (will be discussed later). Following the conclusion of the surface blasting program, the underground blasting proceeded. A typical underground blast started with a 6.5-inch (16.5 cm) diameter center burn hole (that was not loaded) to provide relief (figure 6-a). A line drill perimeter with a diameter of 1 7/8 inch (4.8 cm) and 1 ft (0.3 m) spacing provided extra relief (figure 6-b). Two burn shots each with a 6 ft (1.8 m) advance were then performed around the center hole (figure 6-c). The inset on figure 6-c details each burn. A U round (slabbing) with a 12 ft (3.7 m) advance was then blasted (figure 6-d). A trim round with a 12 ft (3.7 m) advance was blasted to extend the opening to the ribs (figure 6-e). On each figure, # denotes the sequence of blast. Finally, the remaining 2-3 ft (0.6-0.9 m) of rock was removed from the roof by scaling and about 6 ft (1.8 m) of material was removed from the floor by blasting vertical holes (figure 6-f). July/August 2022 The Journal of Explosives Engineering 11