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Vibration Study <br />Primero junior-Senior High School <br />Primero, Colorado <br />A seismogaph was placed in the track and field out building adjoining Primetb <br />Junior-Senior hIigh school on January 22, 2002. The purpose of this vibration study <br />wac to rcco,•d ground vibrations and airblast from blasting activities by Lorencito <br />Coal Company. This vibration study was prompted by a citizens complaint. <br />The seistnograph and air blast mC,nitnr were located at a distance of about 3,000 feet <br />from the blasting at a location between the blasting and the home of the compliant. <br />The equipment waS taken down on Fcbniaty 14, 2002, <br />During this period of time one blast was recvrded for both ground vibrations and <br />airblast. The trigger level for the grvund motion monitor was sett at a level of O.US <br />inches per second (ips). This is a very sensitive trigger level and is far below the <br />regulatory limit. The airblast trigger was set at 130 dB(L). This level is three d13's <br />below the regulatory limit of 133 dB(L) fora 2 FIz or lower flat frequency response <br />microphone.'1'he reason a 130 dB(i.) trigger level was selected was to avoid false <br />triggers from wind gusts chat are frequent in the arcs. <br />The blast that was recorded on February l5, 20U2 at 17:23:38 (5:23 PM) had a peak <br />particle velocity of 0.06 ips. The maximum airblast was 114 dB(L). Ground <br />vibrations and airblast intensities on this order of magnitude are nut capable of <br />causing damage to structures and arc well below the very cvnservutive regulatvey <br />limits- <br />Tu put these results in perspective, the maximum peak panicle velocity of U.U6 ips <br />is only 6 percent of the regulatory limit of 1.0 ips_ Studies by trained reseazchets <br />and experienced observers have never found even the most supe~cial damage at <br />peak particle velocities of less then 0.5 ips. <br />Air6last and sound is a pressure against some. object. In the case of sound it is a <br />pressure against the ear drum. For airblast it is a pressure against a wall or against a <br />window. Tv put the recvrded airblast into perspective, the l 14 dB(L) is the <br />equivalent of the pressure caused by a wind velocity of about 10 MPH. <br />Michael F. Rosenthal <br />Senivr Mining Engineer <br />Office of Surface Mining <br />Denver, Colorado <br />P~ ~ <br />