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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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