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Blasting Impacts and Rock Slope Stability Assessment for Cottonwood Quarry in Grand County, CO <br />to <br />I <br />C A <br />40p <br />t t4 IW moo 1"M <br />Int INr} <br />weichting scala <br />t:.r. <br />A aviShf <br />p t <br />rine 1st <br />Time Histories <br />Ager SL*W and Susxnas, (1974) <br />r+w.Rs IArr <br />F*w iLr Fr egoracy Sp=t t! <br />Figure 3.4 -- Effects of Weighted Filtering on Air -overpressure Records <br />The regulatory limit defined by USBM, as adopted in State of Colorado regulations, for air - <br />overpressure measured with 2 -Hz response seismographs is 133-dBL (0.014 psi). Damage to old <br />or poorly glazed windows does not occur until air -overpressure reaches about 150 dBL. More <br />importantly, since the decibel scale is a logarithmic ratio, the actual overpressure at 150 dBL is <br />0.092 psi, versus 0.013 psi at 133 dBL. Therefore, the actual pressure at the 133-dBL limit, is <br />over seven times (0.091710.0129) lower than the threshold damage level at 150-dBL. The <br />relationships between actual overpressure expressed in psi and decibel scale measurements are <br />shown in the following Equations. NOTE: Due to the logarithmic ratios used to decibel values, <br />seemingly small changes in decibel readings can equate to large changes in absolute <br />overpressure (psi). <br />0=20Log10 PP or P=P 10 ( X20) <br />/o <br />Equation 3.1 <br />Where: dB = decbels, P = werpreswre (psj, Po = Threshold of Hunan Hem rig Pressm (20 miaoPascsfs of 2.9 x 1V psral, <br />REVEY Associates, Inc. page 8 April 2004 <br />