Those neat rows of holes on a mine bench are the entire engineering problem. The explosive is the cheap part. Each hole is drilled into a bench typically 10 to 15 m high, at diameters from 150 mm up to 311 mm on the larger rotary rigs. The geometry comes down to two numbers: - Burden: distance from the hole to the nearest free face, usually 25 to 35 hole diameters - Spacing: distance between holes along a row, commonly 1.1 to 1.4 times the burden Holes are drilled slightly past the intended floor level. That subdrill, roughly 0.3 of the burden, stops the blast leaving a hard toe that shovels and dozers have to fight afterwards. The top third is not explosive at all. It is stemming, angular crushed rock rammed into the collar to stop detonation gases venting straight up the hole. Vent it and you get flyrock, airblast and wasted energy instead of broken rock. Then the mechanism itself. ANFO detonates at roughly 3,200 to 4,500 m/s, pressurising the hole into the gigapascal range. A c...