Reliable initiation of the explosive decomposition of nitroglycerin was a problem from the start. Black powder safety fuses were tested but gave erratic results, so Nobel returned to a detonator that he had patented in 1867 before dynamite was invented. This was a tin capsule containing mercury fulminate that exploded when struck, and when used to detonate dynamite it markedly improved its reliability. During the next few years Nobel produced several strengths of dynamite by using different amounts of nitroglycerin and nitrocotton, but even with the blasting caps there were still problems with accurate and reliable detonation. So inventors turned to electrical detonators.
Electric detonation had been used intermittently since its invention by Watson in 1745; wires contacted the explosive in the cap made incandescent by an electrical current, thereby starting the detonation. Early electrical detonators acted instantly and it was not until 1895 that the delay detonator was invented by H. Julius Smith, who put a short piece of fuse between the ignition charge in the cap and the base charge, thereby creating a delay. This gave miners the ability to detonate charges in a series rather than instantaneously, and eventually sequential explosions were found to be more efficient for breaking a mass of rock than a single, large explosion.
But caution was always the rule when changing blasting practice, and it was not until 1910 that delay detonators were accepted as safe for routine use. Many improvements have been made since then: Detonators are available with any delays that are required; and the scatter in firing times has been reduced to a negligible level.
The dynamite era lasted for 100 years, and during this time the volume of explosives used to break rock increased greatly. Copper ore is a good example. In 1900, 500,000 tons of copper were produced from ore containing about 2% copper, which means that about 25 million tons of ore were mined. In 1913, the Utah Copper Company alone milled 25,000 tpd of copper ore (about 10 million tons per year). This was blasted in open pits, and much more waste was also blasted to give access to the ore. Production rates at open-pit mines grew ever larger as ore grades declined and demand for copper increased, which meant more drilling and blasting. Dynamite broke the rocks efficiently, but the dangers of unexpected explosions and the problems of headaches and nausea that occurred when nitroglycerin came in contact with unprotected skin were always present. It was time for another explosive to be developed that was strong enough to break large volumes of rocks and was cheap, safe, and hygienic. Ammonium nitrate proved to be the answer, and when problems concerning its solubility in water were solved, its sales increased and the dynamite era declined quickly.
Data showing the rise and decline of the dynamite era and the rise of the ammonium nitrate era are given in Table 10.1.