620.09 SEISMIC EFFECTS AND AIR BLAST.

   (a)    Allowable Limits. Allowable limits of ground vibration and sound pressure contained in this section shall be considered not to produce structural damage in any structure.

   (b)    Restrictions on Quantity of Explosives. The use of explosives for blasting purposes within the limitations of these rules and regulations shall only be undertaken with quantities of explosives not in excess of those permitted by this section and except as further restricted by other requirements of these rules and regulations.

   (c)    Ground Vibration Specifications. Blasting operations shall be so conducted that ground vibrations measured at the nearest structure or building, supporting towers and appurtenances, do not exceed a peak particle velocity on any of the three mutually perpendicular planes of motion, i.e., vertical, longitudinal or transverse.

   The blasting shall be conducted so that the ground vibration does not exceed the levels indicated in modified figure B-1, Bureau of Mines, Report of Investigation 8507, set forth below:

       Safe Limit

       V = 2 inches per second

       Energy Ratio = 1.0

               Acceleration in g's

   Frequency of ground motion    Displacement       (Acceleration of
    in cycles per second            in inches         gravity)   

       10          0.0318          0.325

       20          0.0159          0.650

       30          0.0106          0.976

       40          0.0080          1.300

       50          0.0064          1.626

       60          0.0053          1.951

       70          0.0046          2.276

       80          0.0040          2.502

       90          0.0036          2.927

       100          0.0032          3.252

   (d)    Charge Weight; Distance Relations. Explosive charges detonated instantaneously or with delays of eight milliseconds or greater shall be permitted in accordance with the quantities specified in the following table:

       Maximum charge weight per    Minimum permissible
       shot for instantaneous firing    distance from point of
       or per delay for delay firing.    detonation to structure.
       Pounds of Explosive          Feet      

          1             50

          4             100

          9             150

          16             200

          25             250

          36             300

          49             350

          64             400

          81             450

         100             500

          400             1,000

          900             1,500

         1,600             2,000

          2,500             2,500

          3,600             3,000

          4,900             3,500

   The above table is based on scaled distance which is defined as follows:

      Actual distance in feet          D

      Scaled Distance = ——————————————   =   —

      maximum charge per delay       W

      Where    D =    Actual distance in feet from blast to nearest structure.

         W =    Weight in pounds, or the maximum explosive charge per delay, or fired

               instantaneously.

      (1)    If seismograph tests show the peak particle velocity or its equivalent as previously specified in less than fifty percent of safe limit, then blasting operations may continue without further testing provided that the scaled distance for any succeeding shot is not less than the minimum scaled distance during the tests.

      (2)    If the seismograph tests show the peak particle velocity or its equivalent as previously specified to be greater than fifty percent of the safe limit, then all succeeding blasts should be monitored by seismic tests.

   (e)    Allowable Sound Pressure. The maximum allowable sound pressure beyond the construction site resulting from construction blasting shall not exceed 100 decibels.

(Ord. 1968-3. Passed 1-12-68; Ord. 1968-5. Passed 2-27-68.)

   (f)    Whoever violates or fails to comply with any of the provisions of this section is guilty of a misdemeanor of the third degree. Punishment shall be as provided in Section 698.02. A separate offense shall be deemed committed each day during or on which a violation occurs or continues.