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Hit #2 after homeland security THEORY OF EXPLOSIVES In general, an explosive has four basic characteristics: (1) It is a chemical compound or mixture ignited by heat, shock, impact, friction, or a combination of these conditions; (2) Upon ignition, it decom- poses rapidly in a detonation; (3) There is a rapid release of heat and large quantities of high-pressure gases that expand rapidly with sufficient force to overcome confining forces; and (4) The energy released by the detonation of explosives produces four basic effects; (a) rock fragmentation; (b) rock displacement; © ground vibration; and (d) air blast. A general theory of explosives is that the detonation of the explosives charge causes a high-velocity shock wave and a tremendous release of gas. The shock wave cracks and crushes the rock near the explosives and creates thousands of cracks in the rock. These cracks are then filled with the expanding gases. The gases continue to fill and expand the cracks until the gas pressure is too weak to expand the cracks any further, or are vented from the rock. The ingredients in explosives manufactured are classified as: Explosive bases. An explosive base is a solid or a liquid which, upon application or heat or shock, breaks down very rapidly into gaseous products, with an accompanying release of heat energy. Nitroglycerine is an example. Combustibles. A combustible combines with excess oxygen in an explosive to achieve oxygen balance, to prevent the formation of nitrous oxides (toxic fumes), and to lower the heat of the explosion. Chapter 2 EXPLOSIVES 22 Oxygen carriers. Oxygen carriers assure complete oxidation of the carbon in the explosive mixture, which inhibits the formation of carbon monoxide. The oxygen carriers assist in preventing a lowering of the exploding temperature. A lower heat of explosion means a lower energy output and thereby less efficient blasting. Antacids. Antacids are added to an explosive compound to increase its long term storage life, and to reduce the acidic value of the explosive base, particularly nitroglycerin (NG). Absorbents. Absorbents are used in dynamite to hold the explosive base from exudation, seepage, and settle- ment to the bottom of the cartridge or container. Sawdust, rice hulls, nut shells, and wood meal are often used as absorbents. Antifreeze. Antifreeze is used to lower the freezing point of the explosive. Air gap sensitivity. Air gap sensitivity is a measure of an explosive’s cartridge-to-cartridge sensitivity to deto- nation, under test conditions, expressed as the distance through air at which a primed half-cartridge (donor) will reliably detonate an unprimed half-cartridge (receptor). Cap Sensitivity. Cap sensitivity is a measure of the minimum energy, pressure, or power required for initiation of a detonation; i.e., “cannot be detonated by means of a No. 8 test blasting cap when unconfined.” Strength Two strength ratings are used for commercial dynamites. Weight strength compares products on an equal-weight basis, and cartridge strength or bulk strength compares products on an equal-volume basis. Both are expressed in percent, using straight nitroglycerin dynamite as a standard. Complicating this picture is the variety of ingredient mixes among manufacturers, so that 40 percent gelatin dynamite and a 40 percent ammonia dynamite do their work differently; similarly, a 40 percent ammonia dynamite from two different manufacturers will give somewhat different results. Thus, a blaster who had always used one manufacturer’s product could change suppliers and suddenly start complaining about “bad powder.” To further confuse the issue, some manu- facturers continue to use the terms “weight strength” and “bulk strength” as a comparative numerical rating against ANFO at 100. With the advent of new explosives, particularly the ANFOs and the slurries, the dynamite method of judg- ing strength failed to give relevant data. It became necessary to account not only for a product’s relative stored energy, but also its rate of energy release, its gas volume potential, and its heat of detonation. A number of factors are currently used to judge an explosive’s ability to do the work desired, and today’s blaster must con- sider at least the following: Detonation Pressure is a measure of the product’s shock wave energy, influenced by the product’s density (latent energy) and detonation velocity (rate of energy release). Pressure Magnitude or Gas Pressure is a measure of the potential expanding-gas energy, influenced by the product’s density (latent gas volume) and the heat and velocity of detonation (rate of gas production and expansion). Though oversimplified, one way to think of “strength” is to compare an explosive to a mechanical means of breaking and moving rock. We can break rock with a sledgehammer, and a detonation pressure is our explosive hammer. As density increases, the “weight of the hammer” increases; as velocity increases, we “swing the hammer” faster and harder. We can move rock with a bulldozer, and gas pressure is our explosive dozer. As density increases, the dozer gets bigger; as velocity increases, the dozer runs faster—sometimes so fast that it