Dynamite is a mixture of nitroglycerin and/or ethylene glycol dinitrate (hereinafter referred to as "EGDN") along with various nitrate salts and carbonaceous absorbants. Although those in the art frequently use NG to refer to either or both nitroglycerin, EGDN, other nitrate esters or mixtures of these, herein "NG" is used herein to refer to nitroglycerin. Herein, the term "nitrate esters" will be used to indicate a nitrate ester such as nitroglycerin, EGDN, and DNT or mixtures of two or more nitrate esters. Dynamite is a hazardous material, both to manufacture and use. The hazards involved in utilizing dynamite result from its sensitivity. In the explosives art, sensitivity is the relative ease with which a particular explosive may be detonated by a particular impulse, for example, impact, explosion, fire or friction. To lessen the hazard of accidental initiation, the widespread use of ANFO became common in the industry. ANFO is ammonium nitrate fuel oil mixture and is relatively insensitive to detonation except by the use of a booster charge. ANFO had the disadvantage of being deactivated by water. The explosive industry then developed water gels and emulsion explosives based upon the ANFO formulation. These products were both relatively insensitive to accidental detonation and also resistant to deactivation by water.
However, there continue to be many applications where there is no substitute for dynamite. Dynamite has several advantages over ANFO, water gels or emulsions, such as, reliability and energy, which render it very useful. Thus, dynamite continues to be manufactured and sold in large quantities. The two greatest hazards associated with dynamite usage are: (1) impact and friction sensitivity, and (2) a fume generation. Two types of fumes are associated with dynamite. The vapor pressure of both nitroglycerin and EGDN are small but finite and thus vapors escape from the dynamite. These fumes are undesirable because they are physiologically very active and cause headaches, nausea and other discomforts due to their vascular dilating activity. Another type of fume generation is the fume resulting from the reaction products. The fumes can be toxic. The various reactants must be stoichiometrically balanced to prevent formation of the toxic gases carbon monoxide (CO) or the oxides of nitrogen (NO.sub.x). Further, the reaction must proceed essentially to completion to insure complete reaction and prevent formation of toxic gases.
Cartridges of explosives must also propagate in the borehole, i.e. One cartridge exploding must also cause a second adjacent cartridge to detonate. Problems arise in actual use, e.g. due to poor loading conditions. A ragged hole might prevent the second cartridge from being in contact with the first. In this case, the explosive must propagate across an air gap (the separation between the two cartridges). The industry uses a half-cartridge gap test to determine the ability of the explosive to propagate across a gap. Basically, the test requires that one-half of a cartridge of explosive be able to detonate a second half of a cartridge across an air gap. The Bureau of Mines requires that "permissible" explosives, i.e. those approved for use in gassy underground coal mines, must propagate across at least a three-inch gap.
Several explosive companies incorporate dinitrotoluene (DNT) as a "phlegmatizing" (desensitizing) agent in dynamite. Normally, approximately 10% DNT is utilized. Unfortunately, DNT is a suspected carcinogen. Thus, utilization of DNT substitutes a health hazard for increased safety. Furthermore, DNT severely affects the detonation properties of the explosive mixtures, for example, its use severely reduces the detonation velocity. Thus, DNT is not a desirable desensitizing agent based upon possible health hazards and substantial decrease in performance.
Other desensitizers used previously included ethylene oxide adducts. These are handicapped by the "common solvent" technique. This technique uses a compound that is soluble in each of two mutually insoluble compounds to increase the solubility of the two compounds in each other. In dynamite, the mutually insoluble compounds are external water and nitroglycerin. Ethylene oxide adducts are soluble in both. A problem with the ethylene oxide use is that one would expect it to increase the solubility of water into the nitroglycerin, thereby decreasing the water resistance of the dynamite.
The prior art also has utilized dibutyl phthalate as a desensitizing compound for dynamite. The use of dibutyl phthalate has the disadvantage of reduced sensitivity, for example, the dynamite fails to satisfy the three cartridge propagation test. This test consists of placing three cartridges end to end to determine whether detonation will propagate from the end of one cartridge through the end of the third cartridge. Even though dibutyl phthalate has poor sensitivity to propagation as determined by the three cartridge test, dynamites incorporating dibutyl phthalate are more sensitive to initiation by impact than would be expected.
Thus far, the ideal desensitizer for dynamite has escaped the art and would possess the following characteristics. It would (a) be miscible with nitroglycerin, thus keeping the desensitizing agent where it would do the most good, i.e., not migrate away from the nitroglycerin; (b) desensitize the nitroglycerin; (c) be non-toxic; (d) have minimal effect on detonation properties; (e) have a low vapor pressure to aid in suppression of fumes; (f) be water insoluble, thereby preventing degradation in wet environments; (g) be a liquid for ease of handling and measuring; and (h) have a low freezing point such that it would not freeze and separate from the nitroglycerin.
The present invention addresses these needs and provides for the desensitization of dynamite with only minimally reduced detonation performance. Further, the desensitizers of the present invention greatly lower the fumes given off from the product. Significantly, the present invention also improves safety in the production process because the desensitizing agent can be added to the liquid explosive right after nitration which occurs early in the production process.