Blast Airblast Overpressure and Confinement Screen

Airblast scales with the CUBE root of charge weight where ground vibration scales with the square root, and that changes what you can do about it. A spherical pressure wave in air spreads differently from a wave in rock, so charge weight has less leverage on airblast than on vibration: halving a charge buys about 26% more scaled distance where the same halving buys 41% on the ground side. What matters more is confinement and weather. A structure 1,200 ft from a 340 lb delay sits at a cube-root scaled distance of 171.9, and a well-stemmed hole at typical constants reads about 103 dB against a 133 dB limit -- comfortable. CONFINEMENT DOMINATES EVERYTHING ELSE. If the same shot vents through short stemming, an exposed detonating cord trunkline, or a mud seam, the reading rises by 20 dB or more, and because decibels are logarithmic that is TEN TIMES the pressure -- 123 dB here, still under the limit but a different event, and it is the difference between a shot nobody mentions and forty phone calls. No adjustment to the pattern buys that back. The fix is stemming, covered trunklines, and not shooting into a wind or an inversion. Weather is the other multiplier: a temperature inversion or a wind toward the neighbours can focus airblast well above any flat-ground prediction, which is why blast plans carry wind and inversion restrictions no formula replaces. An airblast prediction from generic or site-supplied constants. Airblast is far more variable than ground vibration and far more weather-dependent, and no calculation substitutes for monitoring or for the restrictions in a blast plan. The constants depend heavily on confinement and this cannot know whether a hole will vent. It does not address ground vibration, flyrock, or the structure-response question of what overpressure actually damages what, and decibel limits and their measurement weighting differ between jurisdictions. 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.

cube-root scaled distance = distance / cube root of the charge per delay; overpressure = K x that raised to minus b; decibels = 20 log10(pressure / 2.9e-9 psi); a stated venting penalty in decibels is a factor of ten in pressure every 20 dB.

The cube-root airblast scaling and the decibel conversion against the 2.9e-9 psi reference, by name. Site constants depend heavily on confinement and are entered. 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.

Power-law and logarithm arithmetic on constants the user supplies; no regulatory table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: distance_ft, charge_per_delay_lb, airblast_k, airblast_b, limit_db, confinement_penalty_db, cube_root_scaled_distance, overpressure_db, limit_psi, vented_db, vented_pressure_factor, halving_gain_pct

• Cube root, not square root charge weight is the weak lever on airblast where it is the strong one on vibrationblast physics
• Confinement dominates 20 dB of venting is ten times the pressure, and no pattern change recovers itblasting practice
• Weather focuses airblast inversions and wind produce readings well above any flat-ground predictionblast plan restrictions