Chemical explosives can be classified as low or high explosives. Low (or deflagrating) explosives are used primarily for propelling; they are mixtures of readily combustible substances (e.g., gunpowder) that when set off (by ignition) undergo rapid combustion. High (or detonating) explosives (e.g., TNT) are used mainly for shattering; they are unstable molecules that can undergo explosive decomposition without any external source of oxygen and in which the chemical reaction produces rapid shock waves. Important explosives include trinitrotoluene (TNT), dynamite, nitrocellulose, nitroglycerin, and picric acid. Cyclonite (RDX) was an important explosive in World War II. Ammonium nitrate is of major importance in blasting.
The major use of explosives has been in warfare. High explosives have been used in bombs, explosive shells, torpedoes, and missile warheads. Nondetonating explosives, e.g., gunpowder and the smokeless powders, have found extensive use as propellants for bullets and artillery shells.
The most important peaceful use of detonating explosives is to break rocks in mining. A hole is drilled in the rock and filled with any of a variety of high explosives; the high explosive is then detonated, either electrically or with a special high-explosive cord. Special explosives, called permissible explosives, must be used in coal mines. These explosives produce little or no flame and explode at low temperatures to prevent secondary explosions of mine gases (see damp) and dust. One important explosive used in mining, called ANFO, is a mixture of ammonium nitrate and fuel oil. Its use has revolutionized certain aspects of open-pit and underground mining because of its low cost and relative safety.
Until the 19th cent. gunpowder was widely used in most types of firearms. The invention of various smokeless powders led to the ultimate replacement of gunpowder as a propellant in rifles and guns. Probably the first successful smokeless powder was made by Edward Schultze, a Prussian artillery captain, c.1864. After 1870 it was known as Schultze powder. Its rate of burning was less than that of guncotton because of the partial gelatinization of the powder by a mixture of ether and alcohol; however, it still burned too rapidly for use in rifles. Schultze powder is used in shotguns, blank cartridges, and hand grenades and in igniting the dense, propellant powder used in artillery. The main constituent of Schultze powder is nitrocellulose.
About 1885 a smokeless powder suitable for rifled guns appeared. Invented by Paul Vieille, it was called poudre B and was made from nitrocotton and ether-alcohol. Subsequently, Alfred Nobel added to the growing list of smokeless powders a substance called Ballistite. In Ballistite two of the most powerful explosives known at the time were united; it is made from nitrocotton (with a low nitrogen content) gelatinized by nitroglycerin. Another smokeless powder, cordite, was invented by Sir Frederick Augustus Abel and Sir James Dewar in 1889; it contained a highly nitrated guncotton and nitroglycerin blended by means of acetone. Mineral jelly was added to act as a lubricant. Indurite, invented by Charles E. Monroe in 1891, is made from guncotton and is colloided with nitrobenzine; washing with methyl alcohol frees the lower nitrates from the guncotton.
See T. C. Davis, The Chemistry of Powder and Explosives (2 vol., repr. 1972); J. F. Stoffel, Explosives and Homemade Bombs (2d ed. 1972); R. Meyer, Explosives (3d ed. 1987).
C-4 or Composition C-4 is a common variety of military plastic explosive.
As with many plastic explosives, the explosive material in C-4 is RDX (cyclonite or cyclotrimethylene trinitramine) which makes up around 91% of the C-4 by weight. The plasticizer is diethylhexyl or dioctyl sebacate (5.3%) and the binder usually is polyisobutylene (2.1%).
C-4 is manufactured by combining RDX slurry with binder dissolved in a solvent. The solvent is then evaporated and the mixture dried and filtered. The final material is an off-white solid with a feel similar to modelling clay. The plasticized form of RDX, composition C-4, contains 91% RDX, 2.1% polyisobutylene, 1.6% motor oil, and 5.3% 2-ethylhexyl sebacate.
The Demolition charge M183 is used primarily in breaching obstacles or demolition of large structures where large charges are required (Satchel Charge). The charge assembly M183 consists of 16 block demolition charges M112, four priming assemblies and carrying case M85. Each Priming assembly consists of a five-foot length of detonating cord assembled with two detonating cord clips and capped at each end with a booster. The components of the assembly are issued in the carrying case. The demolition charge M112 is a rectangular block of Composition C-4 approximately by and long, weighing . When the charge is detonated, the explosive is converted into compressed gas. The gas exerts pressure in the form of a shock wave, which demolishes the target by cutting, breaching, or cratering.
Using explosives provides the easiest and fastest way to break the frozen ground. Composition C-4, tetrytol, and TNT are the best explosives for use in northern operations because they retain their effectiveness in cold weather. Dig a hole in the ground in which to place the explosive and tamp the charge with any material available to increase its effectiveness. Either electric or nonelectric circuits may be used to detonate the charge. For a "foxhole", of explosive will usually be sufficient. Another formula is to use 2 pounds (1 kg) of explosive for every 30 cm (1 ft) of penetration in frozen ground.
Because C-4 burns slowly when it is ignited with a flame rather than detonated with a primary explosive, soldiers would sometimes during the Vietnam War era use small amounts of C-4 as fuel for heating rations while on long patrols. While many soldiers used C-4 safely in this manner, there are several anecdotes about soldiers attempting to put out the fire by stomping on it — causing it to detonate.
Michael Herr in Dispatches, his book about the Vietnam War, relates that a soldier would occasionally ingest C-4 from a claymore mine in order to cause temporary illness and be sent on sick leave. Although the ruse might work with an inexperienced commander, experienced officers were usually aware of the trick and would keep the man on board.
C4 has become the most portrayed conventional explosive in several motion pictures and video games.