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How are the blasts measured and recorded?

Ground vibrations and airblasts are measured with a device called a seismometer or seismograph.

These results are then recorded on the seismograph and the highest value of ground vibration (PPV) and airblast overpressure (dB) are obtained. These results are then compared to the limits set forth by Johnson County. It is the blaster’s responsibility to ensure that they are operating within the allowable limits for ground vibration and airblast. The seismographs are set up within the distance of the closest occupied structure. As it relates to quarries, the seismograph is to be set up at an approved location on the quarry property. Seismograph units are required to be calibrated annually as a condition of Johnson County issuing a blasting permit.