For the purpose of this chapter, the following definitions shall apply unless the context indicates or clearly requires a different meaning.
(a) "Acceleration" means a measure of the force exerted by the vibrating earth particle measured in g's. The acceleration of gravity (g-32.2 ft/sec 2).
(b) "Air overpressure" (airblast) is the increase in ambient air pressure resulting from detonation of explosives. It includes high-frequency waves responsible for audible noise and inaudible low-frequency waves which may induce vibration in structures.
(c) "Blast area" is the area in which there is any potential for flying material, air overpressure, or blasting gases to cause injury to persons.
(d) "Components of motion" means ground motion, measured in three mutually perpendicular components, namely:
(1) Longitudinal or radial motion;
(2) Transverse motion;
(3) Vertical motion.
(e) "Contractor" means the person, firm or corporation when engaged in any construction operations involving the use of explosives for blasting purposes under prime contract with owner.
(f) "Controlled blasting" is a method of controlling blast elements including hole size depth, spacing, burden, charge size, charge distribution, and delay sequence to excavate rock to a smooth surface with minimal overbreak.
(g) "Coupling" is the degree to which an explosive fills the cross section of a borehole. A 6-inch explosive in a 6-inch borehole is completely coupled. A 2-inch explosive (surrounded by air) in a 6-inch borehole is "air de-coupled".
(h) "Cushion blasting" is a form of controlled blasting whereby small-diameter columns of explosives or a series of cartridges taped to detonating cord are cushioned by backfilling the annulus of the borehole with sand or dirt. Cushion blasting is generally used to slash narrow benches of rock toward an open rock face.
(i) "Delay" is a distinct pause of pre-determined time between detonation or initiation impulses, to permit the firing of explosive charges separately.
(j) "Displacement" means the amount of ground motion measured in fractions of an inch.
(k) "Energy ratio" means a measure of the kinetic energy of the vibrating earth particle. It is defined as follows:
Energy Ratio — (a/f)2 a-acceleration in ft. per second2 (note not in g's)
f-frequency of vibration tabulated in cycles per second
(l) "Explosive" means any chemical compound or mechanical mixture that is intended for the purpose of producing an explosion, that contains any oxidizing and combustible units
(m) "Frequency" means the number of oscillations of the ground or earth particle that occur in one second, tabulated in cycles per second, c.p.s.
(n) "Fumes" are the gaseous products of an explosion. For the purpose of fume classification only gases such as carbon monoxide, hydrogen sulfide and nitrogen oxides are considered.
(o) "Institute of Makers of Explosives (IME) Fume Classification" is a classification indicating the amount of gases produced by an explosive or blasting agent.
(p) "Line drilling" is a method of controlled blasting in which holes are spaced about 2 to 4 times the hole diameter around the perimeter of the excavation; the holes are generally left unloaded, or may be loaded with light charges of detonating cord, to provide a plane of weakness.
(q) "Longitudinal" or "radial" means motion along a line joining the shot point and point of observation.
(r) "Maximum charge weight per delay" is the maximum total weight of explosive detonated within any timed delay period of minimum 8-millisecond duration.
(s) "Peak particle velocity (ppv)" is the maximum of three single-component blast induced ground motions measured in the vertical, longitudinal, and transverse directions.
(t) "Presplitting" is a blasting technique in which perimeter charges are detonated first in the firing sequence, or as a separate blast ahead of production blasting.
(u) "Scaled distance" is defined as the distance from a blast measured in feet, divided by the square or cube root of the maximum charge weight per delay measured in pounds. Square root scaling shall be used for ground vibration calculations required herein. Cube root scaling shall be used for air overpressure calculations.
(v) "Smoothwall blasting" is a method of controlled blasting in which holes are spaced 18 to 24 inches apart around the perimeter of the excavation; the holes are loaded with low linear charge density, and fired after the main production holes have been blasted.
(w) "Transverse" means motion at right angles to the line joining shot point and point of observation.
(x) "Velocity" means the rate at which the ground or earth particle vibrates measured in inches per second.
(y) "Vertical" means motion up and down.
(Ord. 2005-5-4. Passed 5-3-05.)