Md. Code Regs. 26.21.01.24

Current through Register Vol. 51, No. 22, November 1, 2024

Section 26.21.01.24 - Seismographic Measurements

A. When seismographic measurements are required the following shall apply:

(1) A record of each blast shall be kept.

(2) All records including seismographic reports shall be retained at least 4 years and shall be available for inspection and shall contain the following minimum data:

(a) Name of blasting company or blasting contractor;

(b) Location, date, and time of blast;

(c) Name, signature, Social Security number of blasters;

(d) Type of material blasted;

(e) Number of holes, burden, and spacing;

(f) Diameter and depth of holes;

(g) Type of explosives used;

(h) Total amount of explosives used;

(i) Maximum amount of explosives per delay period of 8 milliseconds or greater;

(j) Maximum number of holes per delay period of 8 milliseconds or greater;

(k) Method of firing and type of circuit;

(l) Direction and distance in feet to nearest dwelling house, public building, school, church, commercial, or institutional building not owned or leased by the person conducting the blasting;

(m) Weather conditions (including such factors as wind direction and cloud cover);

(n) Height or length of stemming;

(o) Mats or other protection used;

(p) Type of detonators used and delay periods used;

(q) The exact location of the seismograph, and the distance of the seismograph from the blast;

(r) Seismographic readings;

(s) Name and signature of person operating seismograph;

(t) Name of person and the firm analyzing seismographic record.

(3) All field seismographs shall record the full analog wave form of the three mutually perpendicular components of motion in terms of particle velocity. All seismographs shall be capable of internal dynamic calibration and shall be calibrated according to the manufacturer's recommendations.

B. Official Tables.

Table I Distance Versus Weight of Explosive Method

Distance to a Building		Weight of Explosive per Delay
Feet Over	Feet Not Over	Pounds
200to 220		34
220to 240		39
240to 250		42
250to 260		45
260to 280		49
280to 300		55
300to 325		61
325to 350		69
350to 375		79
375to 400		85
400to 450		98
450to 500		115
500to 550		135
550to 600		155
600to 650		175
650to 700		195
700to 750		220
750to 800		240
800to 850		263
850to 900		288
900to 950		313
950to 1,000		340
1,000to 1,100		375
1,100to 1,200		435
1,200to 1,300		493
1,300 +		520

Table 2 Distance Versus Peak Particle Velocity Method

Distance		Peak Particle Velocity of Any One Component
Feet Over	Feet Not Over	Inches per Second
0 to100		2.0
100to200		1.75
200to500		1.5
500to1,000		1.0
over 1,000		0.75

Graph I - Maximum Allowable Particle Velocity, inches per second, and Blast Vibration Frequency, H_z

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Md. Code Regs. 26.21.01.24