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Review of Blasting Operations at Denver Brick Company's Golden Mine <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 <br /> damage at level at 150 dB-L. The relationships between actual overpressure expressed in psi <br /> and decibel scale measurements are shown in the following forms of Equation below. <br /> dB = 20 Log,o( P/Po ) or P = 10(da'20) x Po <br /> Where: dB = decibels, P= overpressure (psi), Po= Reference Pressure (2.9 x 101 psi) <br /> we <br /> dB IPA Ift Iftot <br /> u " MMe XW= shaft" • <br /> 170 0.91706 6.3246 Most windows break <br /> 150 0.09171 06325 Some wirxkms Break <br /> 10 _ "door 0 <br /> t30 000917 00632 <br /> 110 0.00092 0.0063 <br /> 1t1M OAM= a0020 <br /> 90 0.00009 0.0006 OSHA Maximum for 8 Hours <br /> 80 CAM O.Mm <br /> Figure 2.7 - Overpressure Effects and Scale Comparisons <br /> 2.3.3 Recommended Vibration and Air Overpressure Limits <br /> Based on prevailing blast vibration control practices used in Colorado and throughout the United <br /> States, regulators and blasting engineers develop vibration and noise limits that will prevent <br /> damage to structures and utilities and minimize annoyance to neighboring properties. <br /> The following equation developed in a U.S. Bureau of Mines Study (RI 8485), airblast can be <br /> used to estimate overpressure, based on charge weight and distance. <br /> Overpressure (psi) = 52.7(D/VV -333)-1.467 <br /> Using this formula, the overpressure at the nearest structure (Area of Concern Neighboring <br /> House#3) at a distance (D)of 800 feet with a 20 pound charge (W)would be 0.0129 psi. In <br /> decibel scale, this air overpressure is between the 130-133 dB level. The intensity of this <br /> overpressure is less than the 0.0129 psi overpressure at the 133 dB limit allowed by the <br /> Colorado regulations. On quiet days, blasting at this level will be heard, however, damage to <br /> structures will not occur at this level.Also due to the location of House#3, the geology creates a <br /> 14 <br />