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c , -3- Throughout this section of the report, no reference has been made to actual vibration levels in terms of the usual single parameter "Peak Particle Velocity", normally expressed in Che U.S. as Inches per Second. This is because the actual levels are expected to be very low, with no risk at all of structural damage, and minimal risk of complaint or human perception. In any event, actual levels can be determined at any time by the use of a suitable blasting seismograph. Vibra-Tech Engineers would not in this instance consider this necessary, but would be able to provide such services if they are required. REGULATORY LIMITATIONS: Vibra-Tech Engineers consider that in the absence of other State or local blast vibration ordinances, the OSM regulations as they limit ground motion and air overpressure should apply, since they are at the same time stringent, effective, proven and offer protection to both the quarry operator and the neighboring householders. The actual vibration levels that will be obtained will not even approach the OSM limitation, however. AIRBLAST: Since no blast was witnessed or monitored, a possible area of concern might be airblast. Airblast, or air overpressure, is commonly thought of not only as noise, but as a possible cause of structural damage. Because much of Che energy in the air overpressure occurs at a low frequency, airblas[ can sometimes be perceived at barely audible levels. Much of the higher frequency airblast, and therefore audible airblas[, is caused by exposed detonating cord on the surface of the shot. It is frequently possible to bury or eliminate this detonating cord, to dramatically reduce perceived blasting noise. Even with large surface mining blasts, however, detonating thousands of pounds of explosves, and generating high air overpressures, damage due to airblast is extremely rare. When damage does occur due to airblast, it is alw~iys caused by air overpressures significantly in excess of 145 dB Linear, and the first appearance of airblast damage is always broken windows. It is likely thaC ttie very small shots detonated by Arkins Park Stone will not be very significant in terms of total energy. Due to the present use of detonating cord i.t is probable that much of this energy will however, be at high, and therefore audible frequencies. CONTROL METHODS: Should it be found necessary to control ground motion, this can be done simply by means of recording seismographs. Although it is unlikely to become necessary, because of [he small explosive weights, and low levels of vibration, further control would be possible by means of mathematical regression analysis of the vibration data, enabling [he analyst to advise Arkins Park Stone of the maximum safe charge weight that may be detonated for any critical distance.