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Review of Blasting Operations at Robinson Brick Company s Siloam Cla. Mine <br /> Overpressure Effects and Equivalent Units <br /> dB-L psi kPa Effect <br /> 180 2.90000 20.0000 Structural Damage . <br /> 170 0.91706 6.3246 Most Windows Break <br /> 160 0.29000 2.0000 <br /> 150 0.09171 0.6325 Some Windows Break <br /> 140 0.02900 0.2000 OSHA Maximum for Impulsive Sound <br /> 134 0.01453 0.1002 Pressure Produced by 20 mph wind <br /> 120 0.00290 0.0200 <br /> 110 0.00092 0.0063 <br /> 100 0.00029 0.0020 <br /> 90 0.00009 0.0006 OSHA Maximum for 8 Hours <br /> 80 0.00003 0.0002 <br /> Figure 2.7--Overpressure Effects and Scale Comparisons <br /> 2.3.3 Controlling Air Overpressure: <br /> Even under ideal conditions, it is difficult to accurately predict airblast with distance. Unlike <br /> vibration predictions where seismic energy is generally proportional to the weight of a confined <br /> charge, airblast is caused by a variety of difficult to predict mechanisms, like venting gases, <br /> moving rock and the vertical component of vibrating ground. It is well known that airblast <br /> intensity is reduced when blast charges are well confined. Conversely, when charges are poorly <br /> confined due to inadequate stemming or by prematurely breaching through open cracks, the level <br /> of airblast is increased. <br /> The following equation developed in a US Bureau of Mines Study (lil 8485), airblast can be used <br /> to estimate overpressure, based on charge weight and distance. <br /> -1 ao, <br /> Overpressure(psi)=52.7(0 333) <br /> GEOTEK& Associates, Inc. Page 16 January 99 <br />