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Review of Blasting Operations at Robinson Brick Company's Siloam Clay Mine <br /> USBM Airblast Limits — (RI 8485, 1980) <br /> Lower Frequency Limit of Measuring System Maximum Level <br /> 0.1 Hertz high pass system Flat Response 134 Peak <br /> 2 Hertz high pass system Flat Response 133 Peak <br /> 5 or 6 Hertz high pass system Flat Response 129 Peak <br /> C-weighted system for events with Slow Response 105 Peak <br /> duration less than 2.0 sec. <br /> Figure 2.6--USBM Recommended Blasting Air Overpressure Limits <br /> 2.3.2 Air Overpressure Limitations: <br /> The regulatory limit defined by USBM, and promulgated by Colorado State Department of Labor <br /> Regulations, for airblast measured with 2-Hz response seismographs is 133 dB-L. As indicated in <br /> Figure 3.2, damage to old or poorly glazed windows does not occur until overpressure reaches <br /> about 150 dB-L. More importantly, since the decibel scale is a logarithmic ratio, the actual <br /> overpressure at 150 dB-L is 0.092 psi, versus 0.013 psi at 133 dB-L. Therefore, the actual <br /> pressure at the 133-dB-L limit, is over seven times (0.092/0.013) lower than the threshold damage <br /> level at 150-dB-L. The relationships between actual overpressure expressed in psi and decibel <br /> scale measurements are shown in the following forms of Equation 3.1. <br /> da. <br /> dB= 20 Logo (710) or P= 10� ""� x P� (Equation 3.1) <br /> Where: dB = decibels, P = overpressure (psi), Po = Reference Pressure (2.9 x 10-9 psi) <br /> GEOTEK& Associates, Inc. Page 15 January 99 <br />