Explosives Technologies

Summary

Explosives, or the more generalized term "high-energy materials," are products that convert chemical energy into physical force through heat, blast, and compression. Explosives are useful in both creation and destruction. They are a key tool used by modern military forces and provide both destructive and propellant forces. A number of industries use explosives for both the separation of materials and the compression and shaping of processed products. There are also commercial applications for explosives, most notably in pyrotechnics and fireworks for both entertainment and commercial displays.

Definition and Basic Principles

Explosives are chemical compounds that contain high levels of stored chemical energy that are released when the stored form is transformed by a catalyst into heat (often accompanied by visible flame) and blast (the sudden overpressurization of the atmosphere around the explosion). While some early explosives were very unstable in their resting form and prone to conversion by the smallest catalyst, modern explosives are relatively safe to handle and will explode only when initiated by specific means of detonation. The relative safety of explosives makes them ideal for uses ranging from constructive to lethal.

With the exception of nuclear reactions, explosives are chemical compounds that are not individually prone to detonation. When combined with other elements, however, the reaction between the chemicals, initiated by an outside promotion, causes the materials to break down their molecular bonds and release their stored potential energy in the form of blast and heat. Nuclear explosions are again an exception in that, besides heat and blast, they also release a large amount of radioactive particles not present in conventional explosions.

Unlike many products that burn or explode when exposed to heat or pressure, explosives are examples of the static potential of chemical energy in that they release their energy only when determined by the user. Instead of uncontrollable reactions, explosives can be manufactured, stored, and used when needed, a safe and predictable application for a potentially dangerous product. Because of their potential to convert mass into heat and energy, explosives are, by definition, a very hazardous product. The usefulness of their properties, however, means that explosives are constantly needed—and improved. Consequently, more powerful explosives are continually developed, and the methods for using them safely also keep pace.

Background and History

The earliest explosive, gunpowder, first appeared in ninth-century China. It was a combination of sulfur, saltpeter, and charcoal. The Chinese used gunpowder for limited military purposes, but its primary purpose was to provide pyrotechnics and fireworks for ceremonial and religious rites. By the thirteenth century, gunpowder was being widely used in European firearms and cannons. Because it was relatively weak, gunpowder had few industrial or commercial uses.

In the 1840s, more potent and complex explosives, such as guncotton (cotton fibers seeped with nitric acid) and nitroglycerin, appeared and were used industrially, such as for mining. Both guncotton and nitroglycerin proved susceptible to spontaneous detonation, however, until mixed with a stabilizing ingredient. Swedish scientist and inventor Alfred Nobel was the first to create a safe, stable, and storable explosive in 1867 when he introduced dynamitenitroglycerin stabilized by absorption of sawdust and containment in a waterproof wrapper.

These early products soon expanded into a wide range of acid-based explosives in the late nineteenth century. Cordite, an explosive commonly used in naval warfare, was a prime example. Unlike the relative instability of guncotton and nitroglycerin, cordite was inflammable, vibration-resistant, and waterproof. Trinitrotoluene, better known as TNT, was another benchmark explosive. Very stable and of a consistency that allows it to be formed into virtually any shape, TNT remains in common use more than a century after its invention.

How It Works

Types of Explosives. Because of the myriad uses for explosive material, the term "explosives" is a general term and not always specific enough. The terminology for high-energy materials relates to the material's use and application. Explosive, as a general term, applies to any product that explodes, but it really refers to a substance intended to alter the form or physical properties of whatever is in its immediate vicinity when it explodes. A specifically placed explosive charge or an explosive used as a warhead in a shell or missile fits this definition.

Explosive reactions can also be harnessed as a propellant to move projectiles toward a target. Simple explosives, like gunpowder used in a firearm, can be used as propellants, but more complex explosives are also used as fuel in missiles and rockets, where the propagation of energy must be sustained over an extended period. Propellants are also used to lift fireworks into the air and as pyrotechnics. This is the colorful burst of light that appears when the firework detonates. In addition to lifting the firework, the formulation of the bursting charge determines the size, pattern, and even the color of the resulting explosion.

Categories of Explosives. Low (or deflagrating) explosives have a relatively slow burning time and tend to generate more heat than blast. Low explosives, such as gunpowder, are commonly used in firearms because their chemical release is contained and will not burst the gun in which they are used. High explosives, which burn quickly and typically release more blast than heat, are used for open-air purposes because the blast needs to dissipate soon after the explosion to avoid unnecessary or undesirable consequences. Instead of burning the application on which the high explosives are used, the blast is intended to shift, move, or remove something. The use of explosives to create mines and tunnels is a good example, as is the use of explosives to level buildings where conventional demolition is too dangerous or time-consuming.

Characteristics of Explosives. How explosives transform into matter and energy is also an element of their type. Low explosives consume their mass through the process of deflagration. The initial ignition of the low explosive creates a concentrated charge of flame that breaks down the molecular bonds of the explosive matter, which, in turn, generates more flame and breaks down the next sequence of molecular bonds. Because the process must move from molecule to molecule, the resulting explosion takes more time, and the low explosives do not dispel all their stored energy at once, producing less blast. The generation of flame over mass is useful in applications that rely on heat, such as using explosives to burn through or sever metal parts. Because flame consumes materials in an irregular fashion, however, low explosives, especially gunpowder, often leave unburned residue as an unwanted byproduct.

High explosives, on the other hand, consume their mass through the process of detonation. The molecular bonds of the explosive material are rapidly broken down by a shock wave passing through it. Because the detonation happens almost simultaneously, the resulting explosion largely occurs before a flame can develop, and most of the explosive potential is released in the form of a blast. This is particularly useful in applications where force transference is the goal, but damage by fire is not desirable. The variations in explosive characteristics permit a wider range of options in selecting the best explosive for a particular purpose. For many military applications, for instance, fire is a useful byproduct of an explosion, so low explosives are best. For purposes that prefer shock over flame, an explosive with a high brisance, or shattering, effect is the ideal option. Brisance is measured and standardized by the speed at which the explosion reaches its maximum force. The faster the propagation of force, the higher the brisance number. Maximum brisance is usually achieved with the aid of an oxidizer, an ingredient that burns at the start of the detonation to accelerate the charge to its maximum heat level at a rate faster than what the explosive would achieve on its own.

Initiation of Explosives. One of the early problems with explosives like nitroglycerin was their instability, which led to accidental explosions, property damage, and deaths. The development of later explosives removed this problem by creating stable explosives that could be safely stored, transported, and handled until detonated. Instead of casual handling, newer explosives required detonation by methods determined by the specialized purpose of the explosives themselves. Many military explosives are detonated by impact with a target that causes compression and initiation of the explosion. Friction is also a detonation method whereby the heat generated by the movement of the explosion causes the explosion. For precisely timed explosions, electrical charges can also detonate high explosives. The electrical charge method allows the use of a timer mechanism or the initiation of a precisely timed sequence of explosions.

Applications and Products

Military Use of Explosives. The military use of explosives has been the primary driving factor in explosives research, as rival militaries attempt to create bigger and better explosions to gain military advantage over a potential enemy. Starting with crude firearms and cannons in the thirteenth century, gunpowder transformed the battlefield by transferring the emphasis of military power from human and animal muscle power to chemical power. Firearms permitted soldiers to attack and defend an area much larger than a hand-operated weapon, such as a spear or bow. The military applications of gunpowder were limited, however, by the relative weakness of gunpowder itself. Only a small percentage of the black powder actually propelled the bullet, while the rest remained in the gun as residue or went out the barrel in a large cloud of dense smoke. To improve their firearms, scientists in the late nineteenth century devised improved propellants, termed "smokeless" powders, that generated virtually no smoke, no residue, and used much more of the powder to propel the bullet downrange.

The invention of more complex and potent explosives in the late nineteenth century transformed war forever. The more lethal explosives coupled with the new internal combustion engine led to the tools of all modern armiesmachine guns, grenades and rockets, heavy artillery, and tanks. Individual soldiers carried more personal firepower with each succeeding generation, and the accompanying heavy weapons also possessed greater ability to distribute explosives around the battlefield. Explosives also caused a decline in defensive warfare. Before gunpowder, a defender inside a stout fortification or castle could withstand the assault of a force several times the size of the defenders. Gunpowder reversed the advantage, as explosives, in sufficient amounts, could defeat any fixed defensive position, causing armies to pursue more mobile strategies. Explosives also went to sea, resulting in modern naval weapons such as large-caliber guns on battleships, torpedoes, and mines. Aerial warfare also developed a wide range of explosive weapons, primarily warheads for bombs and missiles aimed at targets on the ground. Small hand grenades were hurled by pilots during World War I. By World War II, a single B-17 Flying Fortress bomber could carry up to four tons of bombs. Meanwhile, a Cold War-era B-52 Stratofortress could carry up to thirty-five tons. Modern cruise missiles carry a range of potential warheads, including low explosive fragmentation, high explosive blast, and nuclear warheads.

Civilian Use of Explosives. Explosives have a wide range of civilian applications. The earliest and perhaps best known is in the pyrotechnics industry. Fireworks displays are common holiday and event entertainment features, and the evolution of explosives parallels the growing complexity and scale of modern fireworks companies. The railroad and transportation industry also embraces using explosives. When confronted by mountains that defy construction, engineers use explosives to tunnel through them. The appearance of dynamite, the first safe and stable commercial explosive, came just as the expanding railroad system began moving into the mountainous western regions of North America, and its ability to create tunnels made explosives an important tool. The mining industry, also interested in boring holes through mountains, began to use explosives on a large scale. The blast component of explosives proved very valuable in creating tunnels and crushing rock formations to ease the removal of trace ores within.

The construction industry uses explosives to implode large structures. When the traditional demolition of a building is too dangerous, time-consuming, or expensive, carefully placed explosives can topple a building so it falls within a precise footprint, preventing damage to nearby structures. The ability of explosives to demolish buildings also attracted its use by criminal and terrorist organizations. Bombings, ranging from complex remote-detonated bombs to crude "truck bombs," have become common in unstable and contested regions. The spread of terrorism in the early twenty-first century also saw bombings and bombing attempts against Western nations, including by deliberately crashing vehicles such as airplanes for the explosive potential of their fuel.

On a more benign level, explosives also play an unseen role in common items. Small explosive charges, for instance, cause the rapid inflation of an automobile's airbag in case of a collision. On the scientific frontier, explosives in the form of propellants are the only means of lifting large cargoes into space, and heavy rockets consume tons of explosive material to maintain the International Space Station and the array of satellites in orbit.

Careers and Course Work

Because of their complex chemical structures and potentially devastating potential, explosives technology requires advanced and specific training and coursework. Chemistry is the primary field of study that leads to careers in the explosives industry, with jobs trending toward the development of new products and technologies. When using explosives in an occupational setting, knowing how explosives will react and change the environment in which they are used is essential. Structural engineering, for instance, provides knowledge on how explosives can affect or even destroy a structure or building. Conversely, structural engineering can also provide training on building structures resistant to explosive contact. If one is interested in propellants, a background in physics is helpful, as is aerodynamics in the pyrotechnics industry.

The potential hazards associated with explosives also require specialized training. Transporting, storing, and disposing of explosives demands strict safety protocols and knowledge of how to use specialized equipment.

Social Context and Future Prospects

Explosives have an extensive history and a broad future. As a key element of industrialization across centuries, explosives continue to play a role in the development of global economies. As human understanding of the physical world evolves, more potent and potentially lethal explosive technologies emerge for civilian and military applications. Just as explosives joined the internal combustion engine to revolutionize warfare, the overlap of the explosives and electronics fields is creating smaller, smarter, and more lethal explosives. Electronic aiming mechanisms led to the creation of smart bombs capable of steering themselves to a target. As targeting grew more precise, smaller and more discriminate explosives could destroy the targeted adversary but leave civilian life and property unharmed, avoiding unwanted collateral damage. Instead of dropping tons of bombs with a B-52, the US Air Force developed diminutive GBU-39B Small Diameter Bombs big enough to destroy a target yet small enough to avoid excessive blast or fire damage around the target.

As technology evolves, regulatory efforts will continue to emerge at local and international levels. Concerns about terrorists making explosives out of everyday materials have also led to stricter regulations and security measures. However, improvised explosive devices (IEDs) remain a serious concern, killing more civilians each year than any other weapon except firearms. IEDs are simple, unauthorized explosives. The Explosive Weapons Monitor regularly collects and tracks global data concerning deaths and injuries caused by explosives. From October 2010 to September 2020, 28,729 explosive violence incidents causing 357,619 deaths were recorded. Of those, 171,732 civilian and armed actor deaths were the result of IEDs. Further, the Action on Armed Violence (AOAV) reported a 122 percent increase in global civilian explosive weapons casualties from 2022 to 2023, with a 30 percent increase in IED incidents. More than 33,800 civilians were killed or injured, which is the highest total since the organization began its records in 2010. 

The movement to prevent the proliferation of the most powerful explosives—nuclear weapons—remained ongoing, with particular attention to keeping such great destructive power out of the hands of terrorists and rogue regimes such as North Korea's. In the early 2020s, North Korea unveiled an intercontinental ballistic missile believed to be able to reach the United States as well as a submarine-launched ballistic missile. In 2022, the country tested a record number of missiles, and experts estimated by the mid-2020s that the country had between 80 and 90 nuclear warheads.

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