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direction of the person in charge of the blasting. All fuses shall be carefully traced and a <br />search made for the unexploded charges. <br />(E) When electric detonators have been used, workers shall not return to the blast area for at least <br />thirty minutes. All wires shall be carefully traced and a search made for unexploded charges <br />(F) When a completely non -electric initiation system, other than safety fuse, has been used, all <br />employees shall remain away from the blast area for at least 15 minutes. All shock tubes <br />shall be traced and a search made for unexploded charges. <br />(G) When electronic detonators have been used, workers shall not return to the blast area for at <br />least 30 minutes unless the manufacturer recommends additional time before returning to the <br />blast area. <br />(H) If explosives are suspected of burning in a hole, all persons in the endangered area shall move <br />to a safe location and no one shall return to the hole for at least one hour after evidence of <br />combustion ceases. <br />(1) No drilling, digging, or picking shall be permitted until all missed holes have been detonated <br />or the blaster in charge has approved that work can proceed. <br />(.I) Explosive materials recovered from misfires shall not be reused and shall be disposed of in the <br />manner recommended by the manufacturer. <br />6.10 Blasting Vibration and Air -over Pressure Standards <br />(A) In all blasting operations, blasters shall use one of the following methods to control the <br />intensity of motion in the ground at the nearest dwelling, house, school, church, commercial <br />or occupied building. These limits do not apply to property owned, leased, or contracted by <br />the blaster's company or property on which the owner provides a voluntary written waiver <br />from these restrictions. <br />(1) Option 1 (Maximum allowable peak particle velocity) --the intensity of the ground <br />motion, measured with a commercial seismograph, meeting the following standards shall <br />not exceed the limits specified in MAPV column of Table 6.10 A. <br />(a) Monitoring instruments shall have a flat frequency response between 2 and 250Hz for <br />particle velocity. <br />(b) The digitizing sampling rate for peak particle measurements shall be at least 1,021 <br />samples per second. <br />(c) Seismographs shall be capable of performing a self -test of velocity transducers and <br />printed event records shall indicate whether or not the sensor test was successful. <br />(d) Monitoring instruments shall be capable of recording particle velocities with <br />intensities ranging. from 0.02 to 5.0 inches per second. <br />(e) Monitoring systems shall be calibrated by a service center approved by the <br />manufacturer within at least two years of the time of use. Certificates documenting <br />date of calibration, issued by. the approved service center, shall be kept by the user. <br />(t) Monitoring systems shall be capable of printing hard -copy reports showing the date <br />and time of monitoring, the maximum peak particle velocity measurements, and <br />plotted PPV -time waveform plots. <br />(g) For all blasts with scaled distance less than 100 ft, seismographs monitoring motion <br />shall be set to trigger at a level of 0.05 in/s. If a valid vibration record showing <br />compliance with the MAPV limits shown in table 6.10A is not available for <br />53 <br />