Blast Vibration Scaled Distance and Peak Particle Velocity

ScopeA 10,000 lb shot fired on forty delays of 250 lb each produces the vibration of a 250 lb shot. Reading the charge weight per shot into this relation instead of per delay overstates the vibration enormously and is the most common misuse of it. A house 1,200 ft from a shot with 340 lb on the largest single delay sits at a scaled distance of 65.1 ft per square root pound, and at the worst-case site constant (K 242, which PA DEP says to use until your own monitoring supports a lower one) that predicts 0.30 in/s (0.20 on the 160 average curve) -- under a typical 1.0 in/s limit, and above the 55 minimum that 30 CFR 816.67 sets for a structure within 301 to 5,000 ft, so the shot also complies under the no-monitoring path. Work it the other way: at a scaled distance of 55 that house allows 476 lb per delay, so there is room. MOVE THE HOUSE TO 400 FT and the allowance falls to 53 lb, and the 340 lb column has to be decked onto separate delays to comply. Most regulations offer both paths deliberately -- monitor every shot with a seismograph, or stay above a prescribed scaled distance and skip the monitoring -- and the second is conservative by design. The propagation constants are site-specific and vary widely with geology. Generic values can be wrong by a factor of two in either direction, and a site-specific regression from actual seismograph records is the only defensible basis for a production operation; where a regulation requires monitoring this does not substitute for it. It does not evaluate FREQUENCY, and every modern vibration limit is frequency-dependent: the same peak particle velocity is acceptable at 40 Hz and not at 6 Hz, because low frequencies couple into structures. It does not address airblast, which is a separate limit and a separate calculation, or flyrock, and it does not perform a preblast survey, which is what actually resolves damage claims. Blasting is a licensed activity: the blaster in charge, the state and federal explosives regulations, OSM, MSHA or OSHA jurisdiction as applicable, and the site's blast plan govern.

Formula or tablescaled distance = distance / sqrt(charge weight per delay); PPV = K x scaled distance raised to minus b; the largest charge at a required scaled distance = (distance / required SD) squared; the compliant distance = sqrt(charge) x (K / limit) raised to one over b.

Source and editionThe square-root scaled distance and the site propagation relation by name, with the regulatory minimum-scaled-distance compliance path named as an alternative to seismograph monitoring. Site constants are entered; a site-specific regression from seismograph records is the defensible basis. 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.

Free accessPower-law arithmetic on constants and limits the user supplies; no regulatory table is reproduced.

What governsEstimate. AHJ and licensed professional govern.

API field namesdistance_ft, charge_per_delay_lb, site_k, site_b, ppv_limit_in_s, required_scaled_distance, scaled_distance, predicted_ppv_in_s, max_charge_lb, compliant_distance_ft

• Per delay, never per shot delay initiation is what makes the arithmetic work, and the misuse overstates vibration enormouslyblasting practice
• Generic constants can be wrong by a factor of two a site-specific seismograph regression is the defensible basisblasting practice
• Limits are frequency-dependent and this evaluates no frequency at allstate blasting regulation