1507.07 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 this chapter shall only be undertaken with quantities of explosives not in excess of those permitted by this section, except as further restricted by other requirements of this chapter or by order of the Fire Chief or the City Engineer.

   (c)   Safe Limit of Vibration. In all blasting operations, except as otherwise provided, the limit of vibration in any one of three mutually perpendicular components shall be based on a peak particle velocity of two inches per second or an equivalent displacement- frequency relationship, or acceleration-frequency relationship, or energy ratio value. Ground vibration shall not exceed these limits in the immediate vicinity of any structure.

   SAFE LIMIT

   V = 2 Inches Per Second

   Energy Ratio = 1. 0

Frequency of Ground Motion in Cycles per Second	Displacement in Inches	Acceleration in g's (Acceleration of 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

 

   Charge weight - Distance relations

   (d)   Instantaneous and Delayed Detonations. 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 shot for instantaneous firing or per Delay for Delay Firing	Minimum Permissible Distance from Point of 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	1000
900	1500
1600	2000
2500	2500
3600	3000
4900	3500

 

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

   Scaled Distance =    Actual distance in feet    =   

            The square root of the maximum charge per delay

          D

         The square root of 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 is 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 is 100 decibels.

(Ord. 1978-71. Passed 6-13-78.)