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' Blast Vibration Analysis: Proposed MMRR Quarry <br />Page 9 <br />The SDMD light fixtures will be the closest offsite receptors to potential blast vibration and shock <br />' effects. The proposed compliance option (use of Option 4 -Blasting Level Chart, preceded by use <br />of the Scaled Distance Formula for initial blasting) offers only minimal assurances that blast <br />vibration and shock from initial operations will not adversely impact these public safety <br />components. While designed for use under reasonably hazsh environmental conditions (including <br />some minimal roadway vibrations), the lighting poles, fixtures, lamps, and controls were never <br />' designed or intended to be subjected to repeated low frequency vibration shocks with resultant <br />ground velocities well in excess of stipulated maximum levels (see Appendix B) that will result from <br />the proposed quarry operations. <br />The following represent concerns related to sensitive receptors <br />Lamps -numerous lamp suppliers (e.g., GE, Phillips Lighting Company) explicitly state that <br />excessive vibration will lead to shorter HPS lamp life, thus increasing operations and maintenance <br />costs to the District. <br />' Ballast assembly -while generally robust in construction, assured connections between various <br />components could be compromised especially when considering that they (and the lamps) aze located <br />10 feet from the end of a 35-foot moment arm. Such a moment arm will undoubtedly amplify any <br />vibrations resulting from blasting operations producing stresses that the components were not <br />designed to withstand. <br />Photoelectric controls -these components exhibit concerns similaz to those of the ballast assembly <br />noted above. <br />' Lightpole/arm/luminaire assembly -the SDMD lighting fixtures were procured to Pubic Service of <br />Colorado material specifications that stipulate a wind rating of 100 mph with a gust factor of 1.3. <br />However, the forces imposed on these structures by blasting impacts will not necessarilymimic wind <br />loadings. <br />As noted above, the 35-feet high lamp pole and 10-foot extension arm ending in the luminaire fixture <br />represent an enormous moment arm. When subject to a lateral force imposed by ground <br />acceleration, the first response of a structure is to resist motion by virtue of its inertia (mass). The <br />resultant force acting on the pole can be theoretically calculated using Newton's Second Law of <br />Motion: Force = Mass x Acceleration. Thus the greater the mass of the structure, the greater will be <br />the resultant force (given the same acceleration). But the acceleration of any structure, including the <br />lighting assembly, depends on its natural period, which is a function of its mass and stiffness. Taller, <br />more flexible structures have greater periods; shorter stiffer structures have lesser periods. <br />Resonance can occur when the natural period (or frequency) of a structure is excited by an external <br />frequency, which in turn amplifies the original vibration -and its resultant forces. Resonance <br />response by a structure can result in significant damage -this is the principle exhibited when a <br />certain audio frequency is capable of shattering a glass. <br />~ ~ Leonard Rice Engineers, Inc. November 10, 2005 -Job No. 1086BCS03D <br />