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Explosives (Historical Cases)

Explosives (Historical Cases)

Some of the most significant and tragic events in the history of the last few hundred years have involved explosives in the form of bombsdevices used in a deliberate attempt to harm others. The forensic investigation of these incidents has often been a multi-disciplinary affair. Explosives experts and fire investigators are needed to analyze the event itself and discover what kind of device was used and where it may have originated. Bombs typically cause multiple injuries that can be challenging for the forensic pathologist to assess. There has also increasingly been a role for the forensic psychiatrist, as some of those responsible for a bombing are clearly mentally disturbed.

Bombs are often planted by those with political motivations or grudges, working as a group or alone. Their actions, or even the threat of them, cause a great deal of public anxiety and are remembered for a long time. In Britain, one of the first major explosion attempts, the 1605 Gunpowder Plot, is now remembered in the annual celebration of Guy Fawkes, or Bonfire, Night on the fifth of November. Guy Fawkes and his co-conspirators were extremists who wanted to return England to the Catholic faith by blowing up the Houses of Parliament, killing King James I and his government. This bold plan involved rolling 36 barrels into the cellars of the Houses of Parliament. However, one of the group sent a warning letter to a friend in Parliament and this was intercepted and handed to the King. The group was arrested before they could ignite the gunpowder and put to death after trial.

On Bonfire Night, people in Britain burn effigies of Guy Fawkes on bonfires and set off fireworks to commemorate the would-be explosions. It is all harmless fun, many firework displays are now organized by local authorities in the interests of public safety.

In the twentieth century, Britain has suffered terrible losses of life through the bombings of the Irish Republican Army (IRA), a group wanting the re-unification of Northern Ireland and the Irish Republic. On November 21, 1974, bombs exploded in two pubs in central Birmingham, The Mulberry Bush and the Tavern in the Town, killing 21 people and injuring another 182. This was one of the worst IRA atrocities and of special interest because of some forensic issues it raises. The IRA at first claimed responsibility for the bombings, then withdrew their statement. It is widely assumed the group was behind the attack. Police arrested six men known to have associations with IRA personnel in connection with the bombings and they were convicted in 1975. However, the "Birmingham Six" were freed on appeal in 1991. Police and prison officers were found to have extracted false confessions and there was, in fact, no hard evidence of any kind linking the men to the bombing scene. Forensic evidence at the trial had included a positive Griess test for traces of explosives on the hands of two of the suspects. In fact, the results of these tests proved inconclusive and were the subject of some dispute between the forensic experts engaged on the case. No-one else has ever been convicted of the Birmingham pub bombings.

Letter bombs are often the work of one individual who wishes to terrorize others, for whatever reason. Perhaps the most famous case of letter bomb crime involved Theodore Kaczynski, also known as the Unabomber. In the first Unabomber incident, a package found in a University of Illinois parking lot in Chicago on May 25, 1978, exploded, injuring one person. Several similar incidents followed. The first fatality occurred on December 11, 1985, when the owner of a computer company picked up a bomb left outside his business.

A sighting of the Unabomber in 1987 led to a cessation of attacks until 1993 when Kaczynski revealed his anarchist views in a letter to the New York Times. After more bombings and fatalities, the Unabomber was finally caught on April 3, 1996. Forensic psychiatrist Sally Johnson declared Kaczynski fit to stand trial even though he was diagnosed as a paranoid schizophrenic. He was convicted and sentenced to life imprisonment without parole.

Britain's worst ever terrorist incident involved the placing of a bomb on Pam Am Flight 103 over Lockerbie, Scotland, on December 21, 1988. None of the 259 crewmembers and passengers on board survived. Forensic investigation revealed that the U.S.based plane was brought down by a bomb placed in one of the overhead lockers. The plane disintegrated in mid-air, creating 1,200 significant items of debris needing to be investigated. Larger items, such as the engines and the aircraft wings, fell on the town of Lockerbie, producing a fireball and killing 11 people on the ground. Lighter debris was scattered for many miles.

Forensic scientists discovered traces of explosive material in the debris and were able to reconstruct the explosion and the impact it had on the plane. Post-mortem examination of the victims revealed they died of multiple injuries consistent with a mid-air explosion followed by impact on the ground. A former Libyan intelligence officer called Abdel Bassett al-Megrahi was convicted of the bombing and is serving a life sentence in Scotland.

The terror attacks of September 11, 2001, were not the first suffered at New York's World Trade Center. On February 26, 1993, a car bomb was planted in the underground garage below Tower One, killing six people when it went off and injuring over 1,000 others. Analysis revealed the 1300-pound bomb was composed of urea, nitroglycerin, sulfuric acid, aluminium azide, and bottled hydrogen gas. The device was placed in a van and attached to four fuses which the perpetrator, a Kuwaiti man called Ramzi Yousef, ignited with a cigarette lighter. He escaped to Pakistan after the explosion and was involved in many other terrorist attacks before his capture in 1995. He is now held in the same prison as the Unabomber, the ADX Florence maximum security facility in Colorado.

ADX Florence is also the prison where the Oklahoma bomber Timothy McVeigh was held prior to his execution in 2001. Until the attacks of September 11, the Oklahoma bombing , in the nine-story Alfred P. Murrah local government building, was the worst terror incident on U.S. soil. It killed 168 people and injured more than 500 others. The homemade bomb was found to have 2,200 kilograms of ammonium nitrate and fuel oil packed into a hired van. McVeigh, a former soldier, was said to be obsessed with guns and mistrustful of authority. His motive was, apparently, to retaliate against the U.S. government for its part in a siege by the Bureau of Alcohol, Tobacco, and Firearms (ATF ) in Waco, Texas, where 82 members of the Davidian sect were killed.

After September 11, there were two major terror attacks involving bomb explosions, one in Bali and one in Madrid, Spain. The Bali bombing occurred on October 12, 2002, in Paddy's Bar, in the town of Kuta, killing 202 people and injuring another 209, most of them foreign tourists. An electronically-triggered bomb ripped through the bar, driving the injured into the street. A few seconds later, a second, and much more powerful, car bomb went off in front of the Sari Club. This main bomb proved to be made of ammonium nitrate. In 2003, four men were sentenced to death for their part on the bombing, although the sentences have not yet been carried out as of March 2005.

On March 11, 2004, in Madrid, Spain, 191 people died when a string of ten bombs placed in backpacks and carried on four separate commuter trains went off. Later, three more backpack bombs were safely detonated; they had been timed to go off when rescuers and investigators would have been on the scene. More than 1,500 people were injured and many call the event "Spain's 9/11." It is certainly proving a challenge for forensic investigators and reveals how complex a business global terrorism has become.

Twenty-two suspects are being held in Spain and there is debate as to whether an Islamic fundamentalist group like Al Qaeda or the Basque separatist group ETA was responsible for the blasts. The explosive used in the train bombs was a type of dynamite sold in Spain and used in mining. The material resembles that previously used by ETA, although it is a more modern version. Analysis of the backpack bombs showed the explosive was reinforced with shrapnel, and investigators also found a detonator with a cell phone and a timer. The phones have proved a particularly useful source of evidence. Later, a similar unexploded bomb was found on a railway line at Mocejon, 40 miles south of Madrid. The devices had detonators of the type used in the mining industry, although they were made of copper, which is regarded as more sophisticated than the aluminum versions normally used by the ETA group.

The investigation of the Madrid bombings has covered other possibly related incidents, including the discovery in the previous month of a van with 500 kilograms of explosives, and the prevention of a similar attack where multiple bombs would have gone off simultaneously on the commuter trains system. Both of these incidents involved ETA. On the other hand, the near simultaneous attacks of the Madrid bombings were more typical of Al Qaeda. The attack was larger in scale than anything ETA has ever carried out before. Like the IRA, the group generally accompanies its attacks with warnings and claims responsibility for them. In the case of the Madrid bombings, ETA has denied involvement. It is up to the court, backed by expert evidence, to decide who is responsible and, it is to be hoped, convict the perpetrators. Forensic science can do much to help in the "war against terror" as experience is gained through the investigation of the dreadful events of recent years.

see also Bomb damage, forensic assessment; Bomb detection devices; Bomb (explosion) investigations.

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Explosives

Explosives

Explosives are materials that produce violent chemical or nuclear reactions. These reactions generate large amounts of heat and gas in a fraction of a second. Shock waves produced by rapidly expanded gases are responsible for much of the destruction seen following an explosion.

Probably the oldest known explosive is black gunpowder, a mixture of charcoal (carbon), sulfur, and saltpeter (potassium nitrate). When these three chemicals are ignited, a chemical reaction takes place very quickly. The products of that reaction are carbon dioxide, carbon monoxide, sulfur dioxide, and nitric oxide (all gases) as well as potassium carbonate and potassium sulfide (two solids). The four gases formed in the reaction are heated to very high temperatures and expand very rapidly. They form shock waves that have the ability to knock down trees, buildings, people, and other objects in their way. The shock wave also carries with it very hot gases that can burn objects and initiate fires. The combination of shock wave and high temperature is characteristic of most kinds of explosives.

History

Gunpowder was first invented in China no later than about a.d. 850. For hundreds of years, it was used mainly to create fireworks. The Chinese did not use gunpowder as a weapon of war; it was the Europeans who first adapted explosives for use in weapons. By the fourteenth century, Europeans were widely using the explosive as a military device to project stones, spearlike projectiles, and metal balls from cannons and guns.

Words to Know

Chemical explosive: A compound or mixture that releases chemical energy violently and rapidly, creating heat and a shock wave generated by a release of gases.

Dynamite: An explosive made by soaking an inert (inactive or stable), absorbent substance with a mixture of (1) nitroglycerin or ammonium nitrate, (2) a combustible substance (a substance with the ability to burn), such as wood pulp, and (3) an antacid.

Gunpowder: An explosive mixture of charcoal, potassium nitrate, and sulfur often used to propel bullets from guns and shells from cannons.

Nitroglycerine: An explosive liquid used to make dynamite. Also used as a medicine to dilate blood vessels.

Nuclear explosive: A device that obtains its explosive force from the release of nuclear energy.

TNT: Trinitrotoluene, a high explosive.

For the next 500 years, gunpowder was used almost exclusively for pyrotechnic (fireworks) displays and in warfare. Then, in 1856, Italian chemist Ascanio Sobrero (18121888) invented the first modern explosive, nitroglycerin. Sobrero's discovery was, unfortunately for many early users, too unstable to be used safely. Nitroglycerin readily explodes if bumped or shocked.

In 1859, Swedish inventor Alfred Nobel (18331896) began to look for a way to package nitroglycerin safely. His solution was to mix nitroglycerin with an inert (inactive) absorbent material called kieselguhr. He called his invention dynamite.

Virtually overnight, Nobel's invention revolutionized the mining industry. Dynamite was five times as powerful as gunpowder, relatively easy to produce, and reasonably safe to use. For the first time in history, explosives began to be used for a productive purpose: the tearing apart of land in order to gain access to valuable minerals.

Nobel became extremely wealthy as a result of his discovery. But he is said to have been worried about the terrible potential for destruction that his invention had made possible. When he died, he directed that his fortune be used to create the Nobel Foundation, the purpose of which was to bring about lasting peace and advance technology. The Nobel Prizes in various fields of science are now the highest honors that scientists can earn.

Types of explosives

Explosives can be classified into one of four large categories: primary, low, high, and nuclear explosives.

Primary explosives. Primary explosives are generally used to set off other explosives. They are very sensitive to shock, heat, and electricity and, therefore, must be handled with great care. Two common examples are mercury fulminate and lead azide. Primary explosives also are known as initiating explosives, blasting caps, detonators, or primers.

Low explosives. Low explosives are characterized by the fact that they burn only at their surface. For example, when a cylinder of black gunpowder is ignited, it begins burning at one end of the cylinder and then continues to the other end. This process takes place very rapidly, however, and is complete in just a few thousandths of a second.

This property of slowed combustion is preferred in guns and artillery because too rapid an explosion could cause the weapon itself to blow up. A slower explosive has the effects of building up pressure to force a bullet or shell smoothly out of the weapon. Fireworks also are low explosives.

High explosives. High explosives are much more powerful than primary explosives. When they are detonated, all parts of the explosive blow up within a few millionths of a second. Some also are less likely than primary explosives to explode by accident. Examples of high explosives include ANFO (ammonium nitrate-fuel oil mixture), dynamite, nitroglycerin, PETN (pentaerythritol tetranitrate), picric acid, and TNT (trinitrotoluene). They provide the explosive force delivered by hand grenades, bombs, and artillery shells.

High explosives that are set off by heat are called primary explosives. High explosives that can be set off only by a detonator are called secondary explosives. When mixed with oil or wax, high explosives become like clay. These plastic explosives can be molded into various shapes to hide them or to direct explosions. In the 1970s and 1980s, plastic explosives became a favorite weapon of terrorists (people who use violence in order to force a government into granting their demands). Plastic explosives can even be pressed flat to fit into an ordinary mailing envelope for use as a "letter bomb."

Nuclear explosives. Research during World War II (193945) produced an entirely new kind of explosive: nuclear explosives. Nuclear explosives produce their explosive power not by chemical reactions, as with traditional explosives, but through nuclear reactions. In some types of nuclear reactions, large atomic nuclei are split (or fissioned) into two pieces

with the release of huge amounts of energy. In a second type of nuclear reaction, small atomic nuclei are combined (or fused) to make a single large nucleus, again with the release of large amounts of energy.

These two kinds of nuclear explosives were first used as weapons at the end of World War II. The world's first atomic bomb, dropped on Hiroshima, Japan, in 1945, for example, was a fission weapon. The world's first hydrogen bomb, tested at Bikini Atoll in the Pacific Ocean in 1952, was a fusion weapon.

Since the end of World War II, a half-dozen nations in the world have continued to develop and build both fission and fusion weapons. Efforts also have been made to find peaceful uses for nuclear explosives, as in mining operations, although these efforts have not been fully successful.

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Explosives

EXPLOSIVES

EXPLOSIVES date back to the tenth century, when the Chinese used powder, a mixture of saltpeter (potassium nitrate) and sulfur, for fireworks and signals. Europeans began using powder only in the thirteenth century, when Roger Bacon added charcoal to the saltpeter and sulfur, creating "black powder." A century after Bacon, Berthold Schwarz invented a gun by filling an iron tube with black powder and a small pebble, then setting the powder on fire. Bacon's creation was the only known explosive for several hundred years.

Explosives are also used to produce the minerals used to make everything from televisions to paper clips to toothpaste to medicines. The mining and construction industries use "low explosives," which burn at slow rates and are designed to dislodge large pieces of rock and ore. Fireworks and signaling devices are other examples of low explosives. High explosives, which burn at a much faster rate, are used primarily for warfare and can be found in bombs, torpedoes, explosive shells, and missile warheads.

Early Americans used black powder mainly for hunting game. The first powder mill was erected in Massachusetts around 1675. The first recorded blasting took place in 1773.

By the early 1770s, the American colonists were readying for war, but they did not have nearly enough black powder with which to fight. The principal supply was left over from the French and Indian War, and it had to be supplemented with imports of half a million pounds of saltpeter and 1.5 million pounds of black powder. Less than 10 percent of the powder used by the revolutionary armies up to 1778 was produced in the colonies.

Du Pont and Other Nineteenth-Century Figures

This changed with the arrival in America of Eèleuthère Irénée du Pont de Nemours, who began working in a chemical lab in France at age sixteen. In 1802 he brought his expertise in manufacturing gunpowder to Delaware, building his own powder plant, Eleutherian Mills, on the Brandywine River. Two years later he was manufacturing and selling gunpowder. A year after that, his plant was exporting gunpowder to Spain. By 1811 du Pont was the largest manufacturer of gunpowder in America, producing over 200,000 pounds of powder with gross sales of $123,000.

By the early nineteenth century, Americans were no longer using powder strictly for their guns. Expanding frontiers required blasting to construct roads and canals. The discovery of coal in Virginia around 1830 increased the demand for explosives for mining.

Elsewhere in the world, refinements were being made in the process. In 1831, the Englishman William Bickford developed a "safety fuse" that really was not, since it was easily ignited, was unreliable, and sometimes caused fatalities. It was, however, the first efficient detonator, a device that goes off due to shock or heat to create a sufficient force to explode the main charge. Prior to Bickford's safety fuse, mercury fulminate served as the primary detonating compound.

In the late 1840s the Italian scientist Ascanio Sobrero mixed nitric acid and glycerin to come up with nitroglycerin, a highly unstable yet powerful explosive. Alfred Nobel and his father built a small factory in Sweden in 1861 to expand on Sobrero's experiments. In 1866 Nobel combined kieselguhr, the fossilized remains of sea animals, with nitroglycerin to create dynamite, which was significantly more stable than nitroglycerin alone. It was also much faster to ignite, making it one of the first high explosives.

In America, du Pont's grandson Lammot du Pont helped secure his family's place as the predominant manufacturer of explosives when he used the cheaper sodium nitrate instead of potassium nitrate in his powder. During the Civil War he built a plant in New Jersey and produced dynamite, which was three times more powerful than black powder.

Modern Explosives and Their Uses

From the end of the Civil War in 1865 through the end of World War II in 1945, dynamite served as the country's chief engineering tool, allowing mines to be dug deeper and more quickly; quarrying material such as limestone, cement, and concrete; deepening and widening harbors; paving the way for roads and railways; and constructing dams to store water and produce electricity. Dynamite was also instrumental in oil and gas exploration.

The DuPont Company manufactured much of this dynamite until 1911, when a U.S. circuit court found the company to be in violation of the Sherman Antitrust Act. DuPont still accounted for half the nation's total explosives for mining and heavy construction, providing U.S. industry with 840 million pounds of dynamite and blasting powder. During World War I, DuPont supplied 1.5 billion pounds of military explosives to the Allied forces.

In addition to dynamite, trinitrotoluene (TNT) was used extensively in the war effort. Amatol, a mixture of TNT and ammonium nitrate, was used as well, and between the world wars, ammonium nitrate became one of the most important ingredients used in explosives. In the 1940s it became available in an inexpensive form for mixing with fuel oil. This mixture was commonly called ANFO (ammonium nitrate-fuel oil mixtures).

By the 1970s at least 70 percent of high explosives used in the United States contained ammonium nitrate either mixed with fuel oil or in a water gel. These blasting agents are much safer than traditional agents; they produce little or no flame and explode at low temperatures, avoiding potential secondary explosions of mine gases and dust. With its low cost and relative safety, ANFO has helped revolutionize open-pit and underground mining.

Atomic and Nuclear Explosives

In 1945 a test explosion code-named Trinity ushered in the nuclear age of weaponry with the world's first atomic explosion. A plutonium sphere about the size of an orange, produced by 51,000 workers over twenty-seven months, fueled the test. The blast, equivalent to 18,600 tons of TNT, released heat four times that of the sun's interior and was seen 250 miles away.

Three weeks after the test, on 6 August 1945, the United States dropped "Little Boy," with a force of 16,000 tons of TNT, on Hiroshima, Japan. Three days later "Fat Man," equivalent to 22,000 tons of TNT, was dropped on Nagasaki, Japan, signaling the end of World War II in the Pacific theater.

The United States spent $350 billion building 70,000 nuclear warheads through the end of the Cold War in the early 1990s. Atmospheric tests had released radioactive fallout equal to 40,000 times the Hiroshima bomb. Experiments were conducted in the 1960s to find peaceful uses for nuclear explosives but met with little (or no) success.

BIBLIOGRAPHY

Brown, G. I. The Big Bang: A History of Explosives. Gloucestershire, U.K.: Sutton, 1998.

"The Commercial Explosives Industry." The Institute of Makers of Explosives. Available at http://www.ime.org/commercialindustry.htm.

"200 Years of History." E. I. du Pont de Nemours and Co. Available at http://www.dupont.com/corp/overview/history.

T. L.Livermore

Michael Valdez

See alsoArms Race and Disarmament ; Nuclear Weapons ; World War II, Air War against Japan .

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Explosives

EXPLOSIVES

The law of explosives covers dangerously volatile substances, including gasoline, oil, dynamite, and blasting caps filled with highly explosive compounds. Under the police power given to the states through the tenth amendment to the U.S. Constitution, state and local governments may regulate the storing, handling, transportation, and use of explosive substances.

All states require a person or business to obtain a permit before using explosives, such as for a fireworks display or the demolition of a building. State laws and local ordinances criminalize the unlicensed use, storage, sale, and transportation of explosives. Most states provide that unlicensed explosives may be subject to forfeiture, and their possessors subject to fines or incarceration, or both.

States delegate some explosives regulation to municipalities. A municipal corporation may enact provisions for the inspection of explosives and their storage spaces. It may also prescribe the maximum quantity of particular explosives that are allowed to be kept in a particular location.

The U.S. Congress has the authority to regulate explosives in interstate commerce. Under 18U.S.C.A. § 841 et seq., Congress requires a license to import, manufacture, distribute, or store explosive materials that cross state lines. The bureau of alcohol, tobacco, firearms, and explosives, a division of the U.S. justice department, is charged with primary enforcement of the federal laws and regulations regarding explosives.

Explosives are a necessity in a developing world. They allow building contractors to excavate land and clear pathways for road building. However, explosives are inherently dangerous, and, despite strict government regulation, even the authorized use of explosives may cause injuries or property damage. When injury or damage occurs, an aggrieved person may seek redress in civil court.

Under tort law, explosives are considered abnormally hazardous and are subject to strict liability standards. Under strict liability, an explosives operator may be liable for injuries resulting from an explosion regardless of negligence. Not all explosions give rise to this standard. Strict liability may be mandated by statute for injuries resulting from unlicensed explosions. For licensed explosions and accidental explosions, strict liability will be applied where the activity was exceptionally dangerous. For example, a landowner who stores gasoline in a densely populated residential neighborhood may be subject to strict liability, but a business that stores gasoline in an industrial area may not.

Strict liability is not imposed on most licensed explosions. A plaintiff suing for damages resulting from a licensed explosion must prove that the operator did not observe a standard of care commensurate with the danger. This can be proved by showing that the operator failed to comply with statutes or regulations. The plaintiff must also show that the explosion was the proximate dominant, producing, or moving cause for the injury or property damage.

A seller of explosives may be held liable for damage or injury resulting from their use. Manufacturers are held to a higher standard of care than wholesalers or retailers because they are usually more familiar with the formula of the explosive compound and are thus more capable of giving instructions needed for the safe handling, storage, and use of the product. Manufacturers, wholesalers, and retailers must warn buyers of an explosive's dangerous nature by labeling the packaging and including instructions. A manufacturer, wholesaler, or retailer that sells explosives in violation of a statute may be liable to subsequent purchasers of the explosives. For example, a manufacturer or merchant that sells to a minor will be responsible for any injuries resulting from the explosives.

Transporters of explosives may be held liable for damage or injury caused in transit, if they are negligent. Carriers must exercise utmost caution in transporting explosives and follow regulations established by the states. A shipper who hires a carrier for transport may be liable for damage and injury caused by the shipment if the damage and injury were the result of the shipper's negligence. The chain of manufacturer, seller, shipper, and carrier often leads to civil court battles in which each defendant seeks to prove that the others were negligent.

As in any civil case, a defendant in an explosives case may use the defense of "contributory negligence" if the injured party was negligent in some way. For instance, a defendant may invoke contributory negligence if an operator has been adequately instructed but mishandles the explosives. In a small minority of states, contributory negligence by a plaintiff precludes any recovery. In most states," comparative negligence" statutes

allow an amount of recovery reduced by a measure of the plaintiff's negligence. For example, if the plaintiff and defendant were equally at fault, the plaintiff may recover 50 percent of the claim.

A defendant may also seek to argue "assumption of the risk." This means that the injured party was informed of risks but chose to disregard the warnings. For example, a licensed explosives operator who posted notices and warnings according to regulations may escape liability if the plaintiff ignored the signs and entered the explosion site and was subsequently injured in an explosion on the site.

Fireworks are a popular, colorful form of low-impact explosives whose regulation varies from state to state. Minnesota, for example, bans all fireworks except for licensed displays and toy pistols and toy guns containing a negligible amount of explosive compound (Minn. Stat. Ann. §624.20 [West]). Other states are more permissive. Alabama, for example, allows fireworks containing up to 130 milligrams of explosive composition for aerial devices and 50 milligrams for nonaerial devices. Sparklers containing chlorate or perchlorate salts may not exceed a weight of five grams (Ala. Code § 8-17-217).

cross-references

Assumption of Risk; Dominant Cause; Producing Cause; Proximate Cause.

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Explosives

Explosives

An explosive is defined as a substance or mixture of substances that is capable of producing an explosion by itself, without the need for an outside source of oxygen. An explosion is a rapid oxidation reaction that liberates a large quantity of energy and is accompanied by the evolution of a large volume of hot gases and a loud noise. Explosives are often used in criminal and, more particularly, terrorist activities. Crime scene investigators and forensic scientists are called to the scene of an explosion to determine if an explosive was used, and thus, what kind of explosive was used and how it was used. Therefore, knowledge of explosives and their characteristics is paramount for a forensic scientist involved in such criminal investigations.

In general, explosives are classified into two categories: low explosives and high explosives. Low explosives are characterized by a slow rate of reaction, also said to be rapid combustion, resulting in a deflagration. Deflagration is defined as an explosion whose resulting pressure wave travels at subsonic speed (less than 340 meters, or 1,115 feet, per second). These explosives are usually designed to produce a push or to heave a mass. These explosives are also referred to as propellants. Examples of such explosives are black powder, and single-, double-, and triple-base gun powder.

High explosives are characterized by a high rate of reaction resulting in a detonation. Detonation is defined as an explosion whose resulting pressure wave travels at supersonic speed (more than 340 meters, or 1,115 feet, per second). High explosives create a powerful blasting or shattering effect.

High explosives are further classified into primary and secondary explosives depending on their susceptibility to be initiated. Primary explosives are very sensitive to heat or shock and undergo a rapid transition to detonation. They are used to provide the minimum necessary energy to initiate the secondary explosives. Examples of primary explosives include lead azide, lead styphnate, mercury fulminate, and diazodinitrophenol (DDNP). Secondary explosives are much more stable and require a higher initiation energy to be detonated. They will only be detonated by an explosion, such as the one created by a primary explosive. Nevertheless, they are generally more powerful than primary explosives and are thus, mostly used as main charges. Examples of secondary high explosives are 2,4,6-trinitrotoluene (TNT), ammonium nitrate fuel oil (ANFO), cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitramine (HMX), ethyleneglycoldinitrate (EGDN), and pentaerythritoltetranitrate (PETN). Secondary high explosives are designed to destruct by a shattering effect.

Most explosives are used in a combination of two or more explosives, adding the effects of the different types of explosives to the mixture. Dynamite was originally nitroglycerine absorbed into dry silica. Modern formulations of dynamite present some variations, but usually include a mixture of nitroglycerine, nitrocellulose, a fuel/oxidizer mixture, and sometimes EGDN. Semtex is a mixture of RDX and PETN. Amatol is composed of TNT and ammonium nitrate. C-4 is a plasticized composition of RDX. Pentolite is a mixture of TNT and PETN.

Detonating cords are plastic tubes filled with a powder form of explosive. These tubes are often wrapped with fibers to make them more solid. They are mostly used to link different charges by transmitting the shock wave of the detonation. They may also be used as an explosive charge by themselves. In such instances, they are typically used to perform small and accurate destruction. Detonating cords typically use PETN as their explosive content. In some instances, when the cord needs to be used in a medium with a high temperature where PETN would not be suitable, other explosives such as RDX or HMX may be used.

Boosters are defined as the components in the explosion train that propagate and amplify the shock-wave from the detonator to the main charge. They are necessary with some secondary explosives that are insensitive and the shockwave created by the detonator would not be enough to initiate the main charge. Thus, the booster is placed after the detonator and amplifies this detonation, initiating the main charge. Examples of boosters are pentolite or tetryl (2,4,6-trinitrophenyl-methylnitramine).

The forensic analysis of explosives has two interests. On intact material, it is to determine if the material is an explosive. On explosive residues, it is to determine the nature of the explosive and to profile its origin. Identifying the nature of the explosive involved may lead to the author of the crime. Explosives are usually regulated and controlled by the government. Thus, they are not easily obtained by regular citizens. Explosives are often stolen or smuggled from one country to another. Once the nature of the explosives used is identified, it is possible to relate it to recorded thefts or smuggled activities. Some terrorist groups have been known to use one particular explosive consistently, thus allowing the investigation to head one direction or another. Also, when several explosions occur over a certain time span, it is possible to establish links between them if the same explosives have been used.

see also Air plume and chemical analysis; Analytical instrumentation; Biodetectors; Bomb damage, forensic assessment; Bomb (explosion) investigations; Gas chromatograph-mass spectrometer; Oklahoma bombing (1995 bombing of Alfred P. Murrah building); September 11, 2001, terrorist attacks (forensic investigations of); Unabomber case and trial; World Trade Center, 1993 terrorist attack.

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Explosives

Explosives

History

Controlling explosives

Newer explosives

Types of explosives and their sources of power

Four classifications of chemical explosives

Nuclear explosives

Current use and development of explosives

Resources

Explosives are substances (such as compounds and mixtures) that produce violent chemical or nuclear reactions. These reactions generate large amounts of heat and gas in a fraction of a second. Shock waves produced by rapidly expanded gasses are responsible for much of the destruction seen following an explosion.

The power of most chemical explosives comes from the reaction of oxygen with other atoms such as nitrogen and carbon. This split-second chemical reaction results in a small amount of material being transformed into a large amount heat and rapidly expanding gas. The heat released in an explosion can incinerate nearby objects. The expanding gas can smash large objects like boulders and buildings to pieces. Chemical explosives can be set off, or detonated, by heat, electricity, physical shock, or another explosive.

The power of nuclear explosives comes from energy released when the nuclei of particular heavy atoms are split apart, or when the nuclei of certain light elements are forced together. These nuclear processes, called fission and fusion, release thousands or even millions of times more energy than chemical explosions. A single nuclear explosive can destroy an entire city and rapidly kill thousands of its inhabitants with lethal radiation, intense heat, and blast effects.

Chemical explosives are used in peacetime and in wartime. In peacetime they are used to blast rock and stone for mining and quarrying, project rockets into space, and fireworks into the sky. In wartime, they project missiles carrying warheads toward enemy targets, propel bullets from guns, send artillery shells from cannons, and provide the destructive force in warheads, mines, artillery shells, torpedoes, bombs, and hand grenades. So far, nuclear explosives have been used only for tests to demonstrate their force and at the end of World War II in Japan.

History

The first chemical explosive was gunpowder, or black powder, a mixture of charcoal, sulfur, and potassium nitrate (or saltpeter). The Chinese invented it approximately 1,000 years ago. For hundreds of years, gunpowder was used mainly to create fireworks. Remarkably, the Chinese did not use gunpowder as a weapon of war until long after Europeans began using it to shoot stones and spearlike projectiles from tubes and, later, metal balls from cannon and guns.

Europeans probably learned about gunpowder from travelers from the Middle East. Clearly, by the beginning in the thirteenth century gunpowder was used more often to make war than to make fireworks in the West. The English and the Germans manufactured gunpowder in the early 1300s. It remained the only explosive for 300 hundred years; until 1628, when another explosive called fulminating gold was discovered.

Gunpowder changed the lives of both civilians and soldiers in every Western country that experienced its use. (Eastern nations like China and Japan rejected the widespread use of gunpowder in warfare until the nineteenth century.) Armies and navies who learned to use it firstthe rebellious Czech Taborites fighting the Germans in 1420 and the English Navy fighting the Spanish in 1587, for examplescored influential early victories. These victories quickly forced their opponents to learn to use gunpowder as effectively. This changed the way wars were fought and won, and so changed the relationship between peoples and their rulers. Royalty could no longer hide behind stone walled castles. Gunpowder blasted the walls away and helped, in part, to end the loyalty and servitude of peasants to local lords and masters. Countries with national armies became more important than local rulers as war became more deadly, due in large part to the use of gunpowder. It was not until the seventeenth century that Europeans began using explosives in peacetime to loosen rocks in mines and clear fields of boulders and trees.

Other chemical explosives have been discovered since the invention of gunpowder and fulminating gold. The most common of these are chemical compounds that contain nitrogen such as azides, nitrates, and other nitrocompounds.

In 1846, Italian chemist Ascanio Sobrero (18121888) invented the first modern explosive, nitro-glycerin, by treating glycerin with nitric and sulfuric acids. Sobreros discovery was, unfortunately for many early users, too unstable to be used safely. Nitroglycerin readily explodes if bumped or shocked. This inspired Swedish inventor Alfred Nobel (18331896) in 1862 to seek a safe way to package nitroglycerin. In the mid-1860s, he succeeded in mixing it with an inert absorbent material. His invention was called dynamite.

Dynamite replaced gunpowder as the most widely used explosive (aside from military uses of gunpowder). However, Nobel continued experimenting with explosives and in 1875, invented a gelatinous dynamite, an explosive jelly. It was more powerful and even a little safer than the dynamite he had invented nine years earlier. The addition of ammonium nitrate to dynamite further decreased the chances of accidental explosions. It also made it cheaper to manufacture.

These and other inventions made Nobel very wealthy. Although the explosives he developed and manufactured were used for peaceful purposes, they also greatly increased the destructiveness of warfare. Upon his death, his fortune he made from dynamite and other inventions was used to establish the Nobel prizes, which were originally awarded for significant accomplishment in the areas of medicine, chemistry, physics, and peace.

Continued research has produced many more types of chemical explosives than those known in Nobels time: percholates, chlorates, ammonium nitrate-fuel oil mixtures (ANFO), and liquid oxygen explosives are examples.

Controlling explosives

Explosives are not only useless but dangerous unless the exact time and place they explode can be precisely controlled. Explosives would not have had the influence they have had on world history if two other devices had not been invented. The first device was invented in 1831 by William Bickford (17741834), an Englishman inventor. He enclosed gunpowder in a tight fabric wrapping to create the first safety fuse. Lit at one end, the small amount of gunpowder in the core of the fuse burned slowly along the length of the cord that surrounded it. When the thin, burning core of gunpowder reached the end of the cord, it detonated whatever stockpile of explosive was attached. Only when the burning gunpowder in the fuse reached the stockpile did an explosion happen. This enabled users of explosives to set off explosions from a safe distance at a fairly predictable time.

In 1865, Nobel invented the blasting cap, a device that increased the ease and safety of handling nitro-glycerin. Blasting caps, or detonators, send a shock wave into high explosives causing them to explode. In and of itself, blasting caps are a low explosive that is easily ignited. Primers ignite detonators, which burst into flame when heated by a burning fuse or electrical wire, or when mechanically shocked. A blasting cap may contain both a primer and a detonator, or just a primer. Another technique for setting off explosives is to send an electric charge into them, a technique first used before 1900. All these control devices helped increase the use of explosives for peaceful purposes.

Newer explosives

In 1905, nine years after Nobel died, the military found a favorite explosive in TNT (trinitrotoluene). Like nitroglycerin, TNT is highly explosive but unlike nitroglycerin, it does not explode when it is bumped or shocked under normal conditions. It requires a detonator to explode. Many of the wars in this century were fought with TNT as the main explosive and with gunpowder as the main propellant of bullets and artillery shells. Explosives based on ammonium picrate and picric acid were also used by the military.

A completely different type of explosive, a nuclear explosive, was first tested on July 16, 1945, in New Mexico. Instead of generating an explosion from rapid chemical reactions, like nitroglycerin or TNT, the atomic bomb releases extraordinary amounts of energy when nuclei of plutonium or uranium are split apart in a process called nuclear fission. This new type of explosive was so powerful that the first atomic bomb exploded with the force of 20,000 tons of TNT.

Beginning in the early 1950s, atomic bombs were used as detonators for the most powerful explosives of all, thermonuclear hydrogen bombs, or H-bombs. Instead of tapping the energy released when atoms are split apart, hydrogen bombs deliver the energy released when types of hydrogen atoms are forced together in a process called nuclear fusion. Hydrogen bombs have exploded with as much force as 15 million tons of TNT.

Types of explosives and their sources of power

All chemical explosives, whether solid, liquid, or gas, consist of a fuel, a substance that burns, and an oxidizer, a substance that provides oxygen for the fuel. The burning and the resulting release and expansion of gases during explosions can occur in a few thousandths or a few millionths of a second. The rapid expansion of gases produces a destructive shockwave. The greater the pressure of the shockwave, the more powerful the blast.

Fire or combustion results when a substance combines with oxygen gas. Many substances that are not explosive by themselves can explode if oxygen is nearby. Turpentine, gasoline, hydrogen, and alcohol are not explosives. In the presence of oxygen in the air, however, they can explode if ignited by a flame or spark. This is why drivers are asked to turn off their automobile engines, and not smoke, when filling fuel tanks with gasoline. In the automobile engine, the gasoline fuel is mixed with oxygen in the cylinders and ignited by spark plugs. The result is a controlled explosion. The force of the expanding gases drives the piston down and provides power to the wheels.

This type of explosion is not useful for most military and industrial purposes. The amount of oxygen in the air deep in a cannon barrel or a mineshaft may not be enough ensure a dependably powerful blast. For this reason, demolition experts prefer to use explosive chemicals that contain their own supply of concentrated oxygen to sustain the explosion. Potassium nitrate, for example, provides oxygen. Still, if the heat generated by a compound that breaks apart is great enough, the compound can still be an explosive even if it does not contain oxygen. Nitrogen iodide is one of the few examples.

Many chemical explosives contain nitrogen because it does not bind strongly to other atoms. It readily separates from them if heated or shocked. Nitrogen is usually introduced through the action of nitric acid, which is often mixed with sulfuric acid. Nitrogen is an important component of common chemical explosives like TNT, nitroglycerin, gunpowder, guncotton, nitrocellulose, picric acid, and ammonium nitrate.

Another type of explosion can happen when very fine powders or dust mixes with air in an enclosed space. Anytime a room or building is filled with dust of flammable substances such as wood, coal, or even flour, a spark can start a fire that will spread so fast through the dust cloud that an explosion will result. Dust explosions such as these have occurred in silos where grain is stored.

Four classifications of chemical explosives

There are four general categories of chemical explosives: blasting agents, primary, low, and high explosives. Blasting agents such as dynamite are relatively safe and inexpensive. Construction workers and miners use them to clear rock and other unwanted objects from work sites. Terrorists around the world have used another blasting agent, a mixture of ammonium nitrate and fuel oil, ANFO, because the components are readily available and unregulated. Ammonium nitrate, for instance, is found in fertilizers. One thousand pounds of it, packed into a truck or van, can devastate a large building.

Primary explosives are used in detonators, small explosive devices used to set off larger amounts of explosives. Mercury fulminate and lead azide are used as primary explosives. They are very sensitive to heat and electricity.

Low, or deflagrating, explosives such as gunpowder do not produce as much pressure as high explosives but they do burn very rapidly. The burning starts at one end of the explosive and burns all the way to the other end in just a few thousandths of a second. This is rapid enough, however, that when it takes place in a sealed cylinder like a rifle cartridge or an artillery shell, the gases released are still powerful enough to propel a bullet or cannon shell from its casing, though the barrel of the rifle or cannon toward a target hundreds or thousands of feet away. In fact, this relatively slow burning explosive is preferred in guns and artillery because too rapid an explosion could blow up the weapon itself. The slower explosive has the effects of building up pressure to force smoothly the bullet or shell out of the weapon. Fireworks are also low explosives.

High, or detonating, explosives are much more powerful than primary explosives. When they are detonated, all parts of the explosive explode within a few millionths of a second. Some are also less likely than primary explosives to explode by accident. TNT, PETN (pentaerythritol tetranitrate), and nitroglycerin are all high explosives. They provide the explosive force delivered by hand grenades, bombs, and artillery shells. High explosives that are set off by heat are called primary explosives. High explosives that can only be set off by a detonator are called secondary explosives. When mixed with oil or wax, high explosives become like clay. These plastic explosives can be molded into various shapes to hide them or to direct explosions. In the 1970s and 1980s, plastic explosives became a favorite weapon of terrorists. Plastic explosive can even be pressed flat to fit into an ordinary mailing envelope for use as a letter bomb.

Nuclear explosives

The power of chemical explosives comes from the rapid release of heat and the formation of gases when atoms in the chemicals break their bonds to other atoms. The power of nuclear explosives comes not from breaking chemical bonds but from the core of the atom itself. When unstable nuclei of heavy elements, such are uranium or plutonium, are split apart, or when the nuclei of light elements, such as the isotopes of hydrogen deuterium or tritium, are forced together, in nuclear explosives they release tremendous amounts of uncontrolled energy. These nuclear reactions are called fission and fusion. Fission creates the explosive power of the atomic bomb. Fusion creates the power of the thermonuclear or hydrogen bomb. Like chemical explosives, nuclear weapons create heat and a shock wave generated by expanding gases. The power of nuclear explosive, however, is far greater than any chemical explosive. A ball of uranium-239 small enough to fit into a human hand can explode with the force equal to 20,000 tons of TNT. The heat or thermal radiation released during the explosion travels with the speed of light and the shock wave destroys objects in its path with hurricane-like winds. Nuclear explosives are so much more powerful than chemical explosives that their force is measured in terms of thousands of tons (kilotons) of TNT. Unlike chemical explosives, nuclear explosives also generate radioactive fallout.

Current use and development of explosives

Explosives continue to have many important peacetime uses in fields like engineering, construction, mining, and quarrying. They propel rockets and space shuttles into orbit. Explosives are also used to bond different metals, like those in United States coins, together in a tight sandwich. Explosives carefully applied to carbon produce industrial diamonds for as cutting, grinding and polishing tools.

Today, dynamite is not used as often as it once was. Since 1955, different chemical explosives have been developed. Slurry explosives, a relatively new type of explosive, are liquid and can be poured into place. One popular explosive for industrial use is made from fertilizers like ammonium nitrate or urea, fuel oil, and nitric or sulfuric acid. This ammonium nitrate-fuel oil, or ANFO explosive, has replaced dynamite as the explosive of choice for many peacetime uses. An ANFO explosion, although potentially powerful and even devastating, detonates more slowly than an explosion of nitroglycerin or TNT. This creates more of an explosive push than a high velocity TNT blast.

ANFO ingredients are less expensive than other explosives and approximately 25% more powerful than TNT. As of 1995 and continuing into 2006, sale of ANFO components were not regulated as TNT and dynamite were. Unfortunately, terrorists also began using bombs made from fertilizer and fuel oil. Two hundred forty-one marines were killed when a truck loaded with such an ANFO mixture exploded in their barracks in Beirut Lebanon in 1983. Six people were killed and more than 1,000 injured by a similar bombing in the World Trade Center in New York in 1993. In 1995, terrorists used the same type of explosive to kill more than 167 people in Oklahoma City, Oklahoma. In 2004, the Ryongchon disaster in Ryongchon, North Korea occurred because of ANFO. Due to the secretive government in North Korea, the reason that the disaster occurred is still a mystery to the world.

Other explosives in use today include PETN (pentaerythrite tetranitrate), Cyclonite or RDX, a component of plastic explosives, and Amatol, a mixture of TNT and ammonium nitrite.

Nuclear explosives have evolved too. They are more compact than they were in the mid-part of the century. Today they fit into artillery shells and missiles

KEY TERMS

Chemical explosive A substance that violently and rapidly releases chemical energy creating heat and often a shock wave generated by release of gases.

Dynamite A explosive made by impregnating an inert, absorbent substance with nitroglycerin or ammonium nitrate mixed with combustible substance, such as wood pulp, and an antacid.

Gunpowder An explosive mixture of charcoal, potassium nitrate, and sulfur often used to propel bullets from guns and shells from cannons.

Nitroglycerine An explosive liquid used to make dynamite. Also used as a medicine to dilate blood vessels.

Nuclear explosive Device that get its explosive force from the release of nuclear energy.

TNT Trinitrotoluene, a high explosive.

launched from land vehicles. Weapons designers also have created so-called clean bombs that generate little radioactive fallout and dirty bombs that generate more radioactive fallout than older versions. Explosions of neutron bombs have been designed to kill humans with neutron radiation but cause little damage to buildings compared to other nuclear explosives.

Resources

BOOKS

Akhavan, Jacqueline. The Chemistry of Explosives. Cambridge, UK: Royal Society of Chemistry, 2004.

ONeill, Terry, ed. The Nuclear Age. San Diego, CA: Greenhaven Press, 2002.

Townshend, Charles, ed. The Oxford History of Modern War. Oxford, UK, and New York: Oxford University Press, 2005.

Warf, James C. All Things Nuclear. Los Angeles, CA: Figueroa Press, 2004.

Dean Allen Haycock

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Explosives

Explosives

Explosives are substances that produce violent chemical or nuclear reactions. These reactions generate large amounts of heat and gas in a fraction of a second. Shock waves produced by rapidly expanded gasses are responsible for much of the destruction seen following an explosion.

The power of most chemical explosives comes from the reaction of oxygen with other atoms such as nitrogen and carbon . This split-second chemical reaction results in a small amount of material being transformed into a large amount heat and rapidly expanding gas. The heat released in an explosion can incinerate nearby objects. The expanding gas can smash large objects like boulders and buildings to pieces. Chemical explosives can be set off, or detonated, by heat, electricity , physical shock, or another explosive.

The power of nuclear explosives comes from energy released when the nuclei of particular heavy atoms are split apart, or when the nuclei of certain light elements are forced together. These nuclear processes, called fission and fusion, release thousands or even millions of times more energy than chemical explosions. A single nuclear explosive can destroy an entire city and rapidly kill thousands of its inhabitants with lethal radiation , intense heat and blast effects.

Chemical explosives are used in peacetime and in wartime. In peacetime they are used to blast rock and stone for mining and quarrying, project rockets into space , and fireworks into the sky. In wartime, they project missiles carrying warheads toward enemy targets, propel bullets from guns, artillery shells from cannon, and provide the destructive force in warheads, mines, artillery shells, torpedoes, bombs, and hand grenades. So far, nuclear explosives have been used only in war.


History

The first chemical explosive was gunpowder, or black powder, a mixture of charcoal, sulfur , and potassium nitrate (or saltpeter). The Chinese invented it approximately 1,000 years ago. For hundreds of years, gunpowder was used mainly to create fireworks. Remarkably, the Chinese did not use gunpowder as a weapon of war until long after Europeans began using it to shoot stones and spear-like projectiles from tubes and, later, metal balls from cannon and guns.

Europeans probably learned about gunpowder from travelers from the Middle East. Clearly by the beginning in the thirteenth century gunpowder was used more often to make war than to make fireworks in the West. The English and the Germans manufactured gunpowder in the early 1300s. It remained the only explosive for 300 hundred years, until 1628, when another explosive called fulminating gold was discovered.

Gunpowder changed the lives of both civilians and soldiers in every Western country that experienced its use. (Eastern nations like China and Japan rejected the widespread use of gunpowder in warfare until the nineteenth century.) Armies and navies who learned to use it first—the rebellious Czech Taborites fighting the Germans in 1420 and the English Navy fighting the Spanish in 1587, for example—scored influential early victories. These victories quickly forced their opponents to learn to use gunpowder as effectively. This changed the way wars were fought, and won, and so changed the relationship between peoples and their rulers. Royalty could no longer hide behind stone walls in castles. Gunpowder blasted the walls away and helped, in part, to end the loyalty and servitude of peasants to local lords and masters. Countries with national armies became more important than local rulers as war became more deadly, due in large part to the use of gunpowder. It was not until the seventeenth century that Europeans began using explosives in peacetime to loosen rocks in mines and clear fields of boulders and trees.

Other chemical explosives have been discovered since the invention of gunpowder and fulminating gold. The most common of these are chemical compounds that contain nitrogen such as azides, nitrates, and other nitrocompounds.

In 1846 Italian chemist Ascanio Sobrero (1812-1888) invented the first modern explosive, nitroglycerin, by treating glycerin with nitric and sulfuric acids. Sobrero's discovery was, unfortunately for many early users, too unstable to be used safely. Nitroglycerin readily explodes if bumped or shocked. This inspired Swedish inventor Alfred Nobel (1833-1896) in 1862 to seek a safe way to package nitroglycerin. In the mid-1860s, he succeeded in mixing it with an inert absorbent material. His invention was called dynamite.

Dynamite replaced gunpowder as the most widely used explosive (aside from military uses of gunpowder). But Nobel continued experimenting with explosives and in 1875, invented a gelatinous dynamite, an explosive jelly. It was more powerful and even a little safer than the dynamite he had invented nine years earlier. The addition of ammonium nitrate to dynamite further decreased the chances of accidental explosions. It also made it cheaper to manufacture.

These and other inventions made Nobel very wealthy. Although the explosives he developed and manufactured were used for peaceful purposes, they also greatly increased the destructiveness of warfare. When he died, Nobel used the fortune he made from dynamite and other inventions to establish the Nobel prizes, which were originally awarded for significant accomplishment in the areas of medicine, chemistry , physics , and peace.

Continued research has produced many more types of chemical explosives than those known in Nobel's time: percholates, chlorates, ammonium nitrate-fuel oil mixtures (ANFO), and liquid oxygen explosives are examples.


Controlling explosives

Explosives are not only useless but dangerous unless the exact time and place they explode can be precisely controlled. Explosives would not have had the influence they have had on world history if two other devices had not been invented. The first device was invented in 1831 by William Bickford, an Englishman. He enclosed gunpowder in a tight fabric wrapping to create the first safety fuse. Lit at one end, the small amount of gunpowder in the core of the fuse burned slowly along the length of the cord that surrounded it. When the thin, burning core of gunpowder reached the end of the cord, it detonated whatever stockpile of explosive was attached. Only when the burning gunpowder in the fuse reached the stockpile did an explosion happen. This enabled users of explosives to set off explosions from a safe distance at a fairly predictable time.

In 1865, Nobel invented the blasting cap, a device that increased the ease and safety of handling nitroglycerin. Blasting caps, or detonators, send a shock wave into high explosives causing them to explode. It is itself a low explosive that is easily ignited. Detonators are ignited by primers. Primers burst into flame when heated by a burning fuse or electrical wire, or when mechanically shocked. A blasting cap may contain both a primer and a detonator, or just a primer. Another technique for setting off explosives is to send an electric charge into them, a technique first used before 1900. All these control devices helped increase the use of explosives for peaceful purposes.


Newer explosives

In 1905, nine years after Nobel died, the military found a favorite explosive in TNT (trinitrotoluene). Like nitroglycerin, TNT is highly explosive but unlike nitroglycerin, it does not explode when it is bumped or shocked under normal conditions. It requires a detonator to explode. Many of the wars in this century were fought with TNT as the main explosive and with gunpowder as the main propellant of bullets and artillery shells. Explosives based on ammonium picrate and picric acid were also used by the military.

A completely different type of explosive, a nuclear explosive, was first tested on July 16, 1945, in New Mexico. Instead of generating an explosion from rapid chemical reactions , like nitroglycerin or TNT, the atomic bomb releases extraordinary amounts of energy when nuclei of plutonium or uranium are split apart in a process called nuclear fission . This new type of explosive was so powerful that the first atomic bomb exploded with the force of 20,000 tons of TNT.

Beginning in the early 1950s, atomic bombs were used as detonators for the most powerful explosives of all, thermonuclear hydrogen bombs, or H-bombs. Instead of tapping the energy released when atoms are split apart, hydrogen bombs deliver the energy released when types of hydrogen atoms are forced together in a process called nuclear fusion . Hydrogen bombs have exploded with as much force as 15 million tons of TNT.


Types of explosives and their sources of power

All chemical explosives, whether solid, liquid, or gas, consist of a fuel, a substance that burns, and an oxidizer, a substance that provides oxygen for the fuel. The burning and the resulting release and expansion of gases during explosions can occur in a few thousandths or a few millionths of a second. The rapid expansion of gases produces a destructive shockwave. The greater the pressure of the shockwave, the more powerful the blast.

Fire or combustion results when a substance combines with oxygen gas. Many substances that are not explosive by themselves can explode if oxygen is nearby. Turpentine, gasoline, hydrogen, and alcohol are not explosives. In the presence of oxygen in the air, however, they can explode if ignited by a flame or spark. This is why drivers are asked to turn off their automobile engines, and not smoke, when filling fuel tanks with gasoline. In the automobile engine, the gasoline fuel is mixed with oxygen in the cylinders and ignited by spark plugs. The result is a controlled explosion. The force of the expanding gases drives the piston down and provides power to the wheels.

This type of explosion is not useful for most military and industrial purposes. The amount of oxygen in the air deep in a cannon barrel or a mine shaft may not be enough ensure a dependably powerful blast. For this reason, demolition experts prefer to use explosive chemicals that contain their own supply of concentrated oxygen to sustain the explosion. Potassium nitrate, for example, provides oxygen. Still, if the heat generated by a compound that breaks apart is great enough, the compound can still be an explosive even if it does not contain oxygen. Nitrogen iodide is one of the few examples.

Many chemical explosives contain nitrogen because it does not bind strongly to other atoms. It readily separates from them if heated or shocked. Nitrogen is usually introduced through the action of nitric acid , which is often mixed with sulfuric acid . Nitrogen is an important component of common chemical explosives like TNT, nitroglycerin, gunpowder, guncotton, nitrocellulose, picric acid, and ammonium nitrate.

Another type of explosion can happen when very fine powders or dust mixes with air in an enclosed space. Anytime a room or building is filled with dust of flammable substances such as wood , coal , or even flour, a spark can start a fire that will spread so fast through the dust cloud that an explosion will result. Dust explosions such as these have occurred in silos where grain is stored.


Four classifications of chemical explosives

There are four general categories of chemical explosives: blasting agents, primary, low, and high explosives. Blasting agents such as dynamite are relatively safe and inexpensive. Construction workers and miners use them to clear rock and other unwanted objects from work sites. Another blasting agent, a mixture of ammonium nitrate and fuel oil, ANFO, has been used by terrorists around the world because the components are readily available and unregulated. Ammonium nitrate, for instance, is found in fertilizers . One thousand pounds of it, packed into a truck or van, can devastate a large building.

Primary explosives are used in detonators, small explosive devices used to set off larger amounts of explosives. Mercury fulminate and lead azide are used as primary explosives. They are very sensitive to heat and electricity.

Low, or deflagrating, explosives such as gunpowder do not produce as much pressure as high explosives but they do burn very rapidly. The burning starts at one end of the explosive and burns all the way to the other end in just a few thousandths of a second. This is rapid enough, however, that when it takes place in a sealed cylinder like a rifle cartridge or an artillery shell, the gases released are still powerful enough to propel a bullet or cannon shell from its casing, though the barrel of the rifle or cannon toward a target hundreds or thousands of feet away. In fact this relatively slow burning explosive is preferred in guns and artillery because too rapid an explosion could blow up the weapon itself. The slower explosive has the effects of building up pressure to smoothly force the bullet or shell out of the weapon. Fireworks are also low explosives.

High, or detonating, explosives are much more powerful than primary explosives. When they are detonated, all parts of the explosive explode within a few millionths of a second. Some are also less likely than primary explosives to explode by accident. TNT, PETN (pentaerythritol tetranitrate), and nitroglycerin are all high explosives. They provide the explosive force delivered by hand grenades, bombs, and artillery shells. High explosives that are set off by heat are called primary explosives. High explosives that can only be set off by a detonator are called secondary explosives. When mixed with oil or wax, high explosives become like clay. These plastic explosives can be molded into various shapes to hide them or to direct explosions. In the 1970s and 1980s, plastic explosives became a favorite weapon of terrorists. Plastic explosive can even be pressed flat to fit into an ordinary mailing envelope for use as a "letter bomb."


Nuclear explosives

The power of chemical explosives comes from the rapid release of heat and the formation of gases when atoms in the chemicals break their bonds to other atoms. The power of nuclear explosives comes not from breaking chemical bonds but from the core of the atom itself. When unstable nuclei of heavy elements, such are uranium or plutonium, are split apart, or when the nuclei of light elements, such as the isotopes of hydrogen deuterium or tritium , are forced together, in nuclear explosives they release tremendous amounts of uncontrolled energy. These nuclear reactions are called fission and fusion. Fission creates the explosive power of the atomic bomb. Fusion creates the power of the thermonuclear or hydrogen bomb. Like chemical explosives, nuclear weapons create heat and a shock wave generated by expanding gases. The power of nuclear explosive, however, is far greater than any chemical explosive. A ball of uranium- 239 small enough to fit into your hand can explode with the force equal to 20,000 tons of TNT. The heat or thermal radiation released during the explosion travels with the speed of light and the shock wave destroys objects in its path with hurricane-like winds. Nuclear explosives are so much more powerful than chemical explosives that their force is measured in terms of thousands of tons (kilotons) of TNT. Unlike chemical explosives, nuclear explosives also generate radioactive fallout .


Current use and development of explosives

Explosives continue to have many important peacetime uses in fields like engineering , construction, mining, and quarrying. They propel rockets and space shuttles into orbit . Explosives are also used to bond different metals, like those in United States coins, together in a tight sandwich. Explosives carefully applied to carbon produce industrial diamonds for as cutting, grinding and polishing tools.

Today, dynamite is not used as often as it once was. Since 1955 different chemical explosives have been developed. A relatively new type of explosive, "slurry explosives," are liquid and can be poured into place. One popular explosive for industrial use is made from fertilizers like ammonium nitrate or urea , fuel oil, and nitric or sulfuric acid. This "ammonium nitrate-fuel oil" or ANFO explosive has replaced dynamite as the explosive of choice for many peacetime uses. An ANFO explosion, although potentially powerful and even devastating, detonates more slowly than an explosion of nitroglycerin or TNT. This creates more of an explosive "push" than a high velocity TNT blast. ANFO ingredients are less expensive than other explosives and approximately 25% more powerful than TNT. By 1995, sale of ANFO components were not regulated as TNT and dynamite were. Unfortunately, terrorists also began using bombs made from fertilizer and fuel oil. Two hundred forty-one marines were killed when a truck loaded with such an ANFO mixture exploded in their barracks in Beirut Lebanon in 1983. Six people were killed and more than 1,000 injured by a similar bombing in the World Trade Center in New York in 1993. In 1995, terrorists used the same type of explosive to kill more than 167 people in Oklahoma City.

Other explosives in use today include PETN (pentaerythrite tetranitrate), Cyclonite or RDX, a component of plastic explosives, and Amatol, a mixture of TNT and ammonium nitrite.

Nuclear explosives have evolved too. They are more compact than they were in the mid-part of the century. Today they fit into artillery shells and missiles launched from land vehicles. Weapons designers also have created "clean" bombs that generate little radioactive fallout and "dirty" bombs that generate more radioactive fallout than older versions. Explosions of "neutron" bombs have been designed to kill humans with neutron radiation but cause little damage to buildings compared to other nuclear explosives.


Resources

books

Keegan, John. A History of Warfare. New York: Alfred A. Knopf, 1994.

Stephenson, Michael, and Roger Hearn. The Nuclear Casebook. London: Frederick Muller Limited, 1983.

periodicals

Treaster, Joseph B. "The Tools of a Terrorist: Everywhere for Anyone." The New York Times (April 20, 1995): B8.


Dean Allen Haycock

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chemical explosive

—A substance that violently and rapidly releases chemical energy creating heat and often a shock wave generated by release of gases.

Dynamite

—A explosive made by impregnating an inert, absorbent substance with nitroglycerin or ammonium nitrate mixed with combustible substance, such as wood pulp, and an antacid.

Gunpowder

—An explosive mixture of charcoal, potassium nitrate, and sulfur often used to propel bullets from guns and shells from cannons.

Nitroglycerine

—An explosive liquid used to make dynamite. Also used as a medicine to dilate blood vessels.

Nuclear explosive

—Device which get its explosive force from the release of nuclear energy.

TNT

—Trinitrotoluene, a high explosive.

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