Chemical explosives consist of substances that react to produce a self-propagating reaction, that is, one which, once begun, continues on its own at very high rates. The simplest type of explosive, for example, might consist of charcoal (nearly pure carbon) and an oxidizing agent, such as potassium nitrate. When ignited by an outside source of energy, the carbon and potassium nitrate react to form carbon dioxide, and a variety of nitrogen oxides, along with very large quantities of heat. The heat causes the gases to expand very rapidly, moving away from their original location at speeds of a few hundred meters or more per second. The effect of the explosive consists of the intense heat produced by the chemical reaction between fuel and oxidizing agent, the pressure wave produced by the expanding gas, and the impact of solids and gases carried along by the shock wave from the blast.
Chemical explosives are generally categorized as low explosives or high explosives. The primary difference between the two types of explosives is the rate at which the fuel in the explosive reacts with the oxidizing agent. In a low explosive, the fuel is said to deflagrate. Deflagration is a process by which a fuel burns at a rate somewhere between a few centimeters per second to something around the speed of sound (343.2 meters per second). The classic example of a low explosive is gunpowder, which consists of carbon, sulfur, and potassium nitrate. The ignition of gunpowder results in the formation of carbon dioxide, sulfur dioxide, and oxides of nitrogen. Low explosives were once used widely in weapons, as the name “gunpowder” suggests). In modern times, they have a much more limited use, primarily in fireworks, in some types of flares, and in certain types of blasting operations.
High explosives get their name from the very high rate of speed with which the products of ignition are ejected from the reaction site, reaching speeds of almost 9,000 meters per second. High explosives are said to detonate rather than deflagrate. Detonation is a process by which decomposition occurs so rapidly in the explosive mixture that the shock wave generated travels at supersonic speeds (greater than 343.2 meters per second). The first commercially available high explosive was nitroglycerin, invented in 1846. Nitroglycerin is very unstable, however, and came into widespread use only in the late nineteenth century when Swedish chemist Alfred Nobel found a way to stabilize the material in a new product known as dynamite. Some of the most popular high explosives are, in addition to nitroglycerin and dynamite, ANFO (ammonium nitrate-fuel oil mixture), C-4, HMX (cyclotetramethylene-tetranitramine), PETN (pentaerythritol tetranitrate), picric acid, Semtex, and TNT (trinitrotoluene).
Nuclear explosives are a subclass of high explosives in that they produce heat, light, sound, and pressure waves that travel at very high rates of speed. They differ from chemical explosives in the way these products are produced. Rather than a chemical reaction, a nuclear explosive occurs because of one of two nuclear reactions, fission or fusion. Fission is a nuclear reaction in which the nuclei of high-atomic-number elements, such as uranium and plutonium, break into smaller parts, with the release of large amounts of energy. Fusion is a nuclear reaction in which two small nuclei, such as those of hydrogen and/or helium, combine with each other to form a larger nucleus, again with the release of large amounts of energy. Nuclear explosives are many hundreds or thousands of times more powerful than are the most powerful chemical explosives. For example, the power of a nuclear bomb is generally expressed in TNT equivalents, that is, the thousands of tons of TNT needed to produce an explosion of the size of some given nuclear weapon. As an example, the fission bomb the United States dropped on Hiroshima, Japan, on August 6, 1945, was ranked as a 15 kiloton bomb, not because it weighed 15 kilotons, but because it had the explosive power equal to 15,000 tons of TNT. The first fusion bomb tested by the United States was ranked as a 25 megaton bomb because it had the explosive power of 15,000,000 tons of TNT.
Peacetime use of explosives is responsible for a relatively small number of deaths and injuries in the United States and other parts of the world each year. Such cannot be said, of course, for the use of explosives in war zones. Each year, a handful of people are killed by explosives in the United States in home accidents (as when a propane tank explodes) or in the workplace (in factories where explosives are manufactured). Overall, however, the most important source of accidents due to explosives is in the use of fireworks. In the United States in 2011, four deaths were attributed to the improper use of explosives, and an estimated 9,600 emergency-department visits were attributed to injuries sustained during the use of explosives. These numbers remained relatively constant between 1991 and 2011.
The earliest explosive used by humans was a form of gunpowder with roughly the same combination, known as black powder. Records suggest that black powder was invented by the Chinese as early as the tenth century, after which its formulation and uses were carried to Europe. The first precise formulation of the content of black powder was apparently provided by English naturalist Roger Bacon in 1242. Black powder remained essentially the only practical explosive until the invention of nitroglycerin by Italian chemist Ascanio Sobrero in 1846. Nobel's development of dynamite in 1867 finally provided a safe and efficient way of handling and using the powerful nitroglycerin. During the last half of the nineteenth century, a number of other explosives were also developed, including nitrocellulose (1846), trinitrotoluene (TNT; 1863), ballistite (1888), and cordite (1889). The most widely used explosives in the early 2000s in addition to these early products were produced primarily after the conclusion of World War II, including ANDO, C-4, HMX, PETN, and Semtex.
The primary peacetime use for explosives is in the coal industry, which uses about two-thirds of all the explosives produced in the United States. Explosives are also used for blasting in other types of resource recovery, such as metal and nonmetal mining and quarrying (24%). Construction projects account for an additional seven percent of all explosive use in the United States, and miscellaneous uses for the remaining three percent. The category of miscellaneous uses includes a number of perhaps less well-known applications, such as in ejector seats for spacecraft, airbags in commercial vehicles, and fire suppression systems.
Akhavan, Jacqueline. The Chemistry of Explosives, 3rd ed. London: Royal Society of Chemistry, 2011.
Cooper, Paul W. Explosives Engineering, 2nd ed. New York: John Wiley, 2011.
Kelly, Jack. Gunpowder: Alchemy, Bombards, and Pyrotechnics: The History of the Explosive That Changed the World. New York: Basic Books, 2009.
Matyás, Robert, and Jirí Pachman. Primary Explosives. New York: Springer, 2013.
Lima, D. R., et al. “Impact of Ammunition and Military Explosives on Human Health and the Environment.” Reviews on Environmental Health 26, no. 2 (2011): 101–10.
Rappert, B., R. Moyes, and I. Lang. “The Case for Addressing Explosive Weapons: Conflict, Violence and Health.” Social Science and Medicine 75, no. 11 (2012): 2047–54.
Rylott, E. L., A. Lorenz, and N. C. Bruce. “Biodegradation and Biotransformation of Explosives.” Current Opinion in Biotechnology 22, 3. (2010): 434–40.
Centers for Disease Control and Prevention. “Explosions and Blast Injuries: A Primer for Clinicians.” http://www.cdc.gov/masstrauma/preparedness/primer.pdf (accessed October 11, 2012).
Consumer Product Safety Commission. “2011 Fireworks Annual Report.” http://www.cpsc.gov/library/2011fwreport.pdf (accessed October 11, 2012).
GlobalSecurity.org . “Explosives.” http://www.globalsecurity.org/military/systems/munitions/explosives.htm (accessed October 11, 2012).
Society of Explosives Engineers. “The World of Explosives.” http://www.explosives.org/ (accessed October 11, 2012).
International Society of Explosives Engineers (ISEE), 30325 Bainbridge Rd., Cleveland, OH, 44139, (440) 349-4400, Fax: (440) 349-3788, http://www.isee.org .
David E. Newton, EdD