Blasting Powder Factor and Explosive Load per Hole

The pattern and the hole do the work together: burden and spacing set how much rock a hole is responsible for, diameter and explosive density set how much energy is in it, and powder factor is the ratio. An 8 by 10 ft pattern on a 30 ft bench with 3.5 in holes, ANFO at 1.25 specific gravity, 2.4 ft of subdrill and 5.6 ft of stemming in 165 pcf rock loads 5.21 lb per foot over a 26.8 ft column -- 140 lb in a hole that owns 198 tons, a powder factor of 0.705 lb per ton. Push the pattern to 9 by 11 and the same hole covers 245 tons and the factor drops to 0.570: cheaper per ton, and the point at which fragmentation starts to suffer and the loader tells you before the spreadsheet does. THE TWO LENGTHS THAT DO NOT APPEAR IN THE PATTERN matter as much as the ones that do. Subdrilling below grade, typically a third of the burden, keeps the toe from being left high, and a shot that leaves toe costs more in secondary breakage than the extra drilling ever did. Stemming, typically about seven tenths of the burden, keeps the gases in the hole long enough to break rock instead of venting -- short stemming is the direct cause of flyrock and airblast. And the charge weight per hole is the number that goes into the vibration check, per DELAY rather than per shot. Pattern and charge arithmetic for a vertical production hole with a single continuous column charge. It does not design a blast, select an explosive, evaluate its suitability for wet holes, handle decked charges, air decks, or bottom-loaded holes with different products, or account for hole angle, which changes the true burden. It does not predict fragmentation, which powder factor is a proxy for and which depends on rock structure, jointing, and initiation timing far more than on the ratio, and it does not evaluate vibration, airblast, or flyrock, none of which are optional. Blasting is a licensed activity: the blaster in charge, the state and federal explosives regulations, MSHA or OSHA jurisdiction, and the site's blast plan govern.

loading density lb/ft = (pi / 4) x (diameter / 12) squared x 62.4 x explosive specific gravity; charge length = bench height + subdrill - stemming; charge weight = the product; rock tons per hole = burden x spacing x bench height x rock density / 2,000; powder factor = charge weight / tons.

The standard powder-factor relations by name, with 62.4 lb per cubic foot as the water reference an explosive's specific gravity is taken against and 2,000 lb per ton. Pattern and charge arithmetic only for a vertical hole with a single continuous column charge. Blasting is a licensed activity: the blaster in charge, the state and federal explosives regulations, MSHA or OSHA jurisdiction, and the site's blast plan govern.

Geometry and density arithmetic on the user's own pattern and product data; no explosive manufacturer table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: burden_ft, spacing_ft, bench_height_ft, hole_diameter_in, subdrill_ft, stemming_ft, explosive_sg, rock_density_pcf, hole_count, loading_density_lb_per_ft, charge_length_ft, charge_weight_lb, rock_tons_per_hole, powder_factor_lb_per_ton, rock_volume_cy

• Powder factor is comparable, a pattern is not which is why it is the number carried across shots and yearsblasting practice
• Subdrill pays for itself a shot that leaves toe costs more in secondary breakage than the extra drillingblasting practice
• Charge weight enters vibration PER DELAY not per shot, and the difference is enormousblasting practice