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v1.0.2 / 01 jul 02 / greg goebel / public domain
* Explosives, pyrotechnics, and fireworks -- chemical materials and devices to create fire, smoke, light, heat, noise, or explosions -- have been an important technology for centuries, and continue to be improved. This document provides a short survey.
* The term "pyrotechnics" means "science of fire", and in principle covers all chemical devices and materials whose purpose is to burn and produce an explosion, fire, light, heat, noise, or gas emission. Following this definition, "explosives" are pyrotechnic materials that cause an explosion, and "fireworks" are pyrotechnic devices used for entertainment.
However, the actual usage of these words is a little more confusing and inconsistent. The best way to define them is by description:
Pyrotechnic devices include matches; flares; smoke grenades; airbag inflators; military incendiaries; solid rockets; fuel pellets for field stoves and other heating units; and quick-release devices used for emergency exit systems in aircraft, or for staging and shroud ejection systems in space launch vehicles.
Explosive materials are used as "bursting charges" for bombs, missile warheads, grenades, and mines; and as "propellants" to fire bullets and artillery shells. They are used as "blasting charges" in military or commercial demolition, for earth-moving for engineering projects, and demolition of buildings and other structures.
Explosives are categorized as "low" or "high" explosives. In low or "deflagrating" explosives, such as black powder, the explosion propagates through the material at subsonic speed through an accelerated burning or "combustion" process. In high explosives, such as TNT, the explosion propagates by a supersonic "detonation", driven by the breakdown of the molecular structure of the material.
An explosive can be characterized by the amount of energy it releases when detonated, as well as by its shearing and shock effect, or "brisage".
Most modern high explosives are "stable" or "insensitive", meaning they are difficult to set off by accident. A high-explosive charge generally needs an easily-activated "detonator" or "blasting cap" to cause it to explode, and sometimes may also need a secondary "booster charge" of intermediate sensitivity that is triggered by the detonator to initiate the full explosion. Propellants equivalently need a "primer" and sometimes a secondary "ignition charge" to set them off.
* Most pyrotechnics and low explosives operate by combustion processes, in which a fuel combines with oxygen to release heat, light, smoke, or gas. In such materials, a "fuel" component that burns is mixed with an "oxidizing" component that releases oxygen when heated, since combustion rates would be limited if the fuel had to rely on atmospheric oxygen for combustion. For example, the fuel in black powder is charcoal and sulfur, while the oxidizer is potassium nitrate (KNO3).
The packaging of a pyrotechnic mixture affects its behavior. Confinement greatly speeds up the combustion process by concentrating heat and hot gas in the reaction. In fact, black powder will simply burn rather than explode unless packed into an appropriate casing, such as the thick paper shell of a firecracker.
Burning rate is also increased by the homogeneity of the mixture. Fine powders burn faster than coarse grains. Liquid explosives are unsafe because they are extremely homogenous; their mixing is at the molecular level, and so they can be set off by a mild physical shock. Liquid explosives also tend to settle and separate in storage, which changes their chemical properties, and not generally for the better.
Adding abrasives to an explosive material makes it more sensitive, while adding lubricants like wax makes it more stable. Materials that reduce explosive sensitivity are known as "stabilizers" or "moderators".
* Most high explosives operate by a chemical breakdown in their molecular structure, rather than a combustion process between fuel and oxidizer. For example, nitroglycerine has the molecular formula C3N3H5O9. Any small disturbance, such as heat or physical shock, causes it to decompose into carbon dioxide (CO2), water (H2O), nitrogen (N2), and a little excess oxygen (O2).
This process still involves oxidation reactions, but the oxygen is part of the molecule. In the breakdown of nitroglycerine, nitrogen-oxygen atomic bonds are replaced by far more stable carbon-oxygen, hydrogen-oxygen, and nitrogen-nitrogen bonds, with the process accompanied by a violent release of energy.
* Many pyrotechnics, such as flares and fireworks, are designed to emit light. Pyrotechnic materials emit light by two processes: incandescence and line emission.
Incandescence, or "blackbody radiation", occurs when solid or liquid particles are heated, causing them to emit a broad spectrum of radiation. The higher the temperature, the higher the peak frequency of the emission. As a particle grows hotter, it will glow red, orange, yellow, white, and finally blue. The total energy output of an incandescent particle is also proportional to the fourth power of the temperature, which means that making the combustion twice as hot makes it sixteen times as bright.
Line emission, in contrast, occurs in a hot gas, and produces light through changes in internal electron levels, with light emitted only at specific frequencies characteristic of the type of atom or molecule making up the gas. If the light frequencies occur in the visible range, they will correspond to fairly pure colors.
* Pyrotechnic materials can be ignited by flame, friction, impact, electrical shock, high ambient temperatures, or even a laser beam. In general, high explosives are designed to be insensitive. They can't be set off by a flame or spark, and have to be set off by a shock from a detonator.
* Certain "pyrotechnic" metals, such as magnesium and aluminum, ignite at very high temperatures and burn very hot, releasing large amounts of energy. For this reason, aluminum powder is sometimes added to explosives to enhance blast effect.
* While people have devised fiery and smoke-making materials for most of recorded history, the first pyrotechnic material worthy of the name was black powder, developed by the Chinese more than 1,000 years ago. The Chinese used it to make firecrackers and rockets for public entertainment and to frighten enemies in combat.
Black powder migrated to the West in the Middle Ages. The English monk Roger Bacon described a formula for it in 1242, writing in code because of the deadly nature of the material. In the 14th century, black powder led to the development of new weapons, though several more centuries would pass before it was used in mining and quarrying, when the technology was finally developed to bore holes in hard rock to place explosives.
In weapons, black powder was used as a bursting agent and a propellant. Black powder charges were used as "petards", or mines, to break down the walls of fortifications, and later as filler in explosive shells and hand grenades. As a propellant explosive, black powder was used to fire balls from muskets, as well as stones from primitive cannon called "bombards", which eventually evolved into muzzle-loading artillery. Black powder became god of war, and remained so until the last decades of the 19th century.
* Early mixtures of black powder consisted of equal weights of charcoal, sulfur, and saltpeter. Saltpeter is a shiny white crystalline material that is found on the walls of caves or in well-aged manure piles; today it is known as potassium nitrate (KNO3). Eventually, the formula for black powder was refined to a mix of charcoal, sulfur, and saltpeter in the proportions 15:10:75 by weight.
Black powder is an excellent explosive in many respects. Its raw materials are cheap, abundant, nontoxic, and environmentally safe. It is stable and can be stored indefinitely if kept dry. It can be easily ignited with a spark or fuze, though this is by no means entirely a virtue.
Black powder also has a number of limitations:
Better explosives were needed and were developed, beginning in the middle of the 19th century. However, the low cost and good properties of black powder make it still the material of choice for fireworks, as will be discussed later.
* In 1846, an an Italian chemist named Ascanio Sobrero added glycerol to a mixture of nitric and sulfuric acids, setting off an explosion that nearly killed him. He had discovered the first high explosive. Sobrero to no surprise decided that the liquid he called "nitroglycerine" was dangerous. He tried to keep it a secret.
He failed. A Swedish chemical manufacturer named Alfred Nobel began to produce nitroglycerine for rock blasting in 1863. Nitroglycerine can't be detonated by a simple cord fuze, and so in 1865 Nobel devised the first detonator, a blasting cap consisting of a small black power charge with a cord fuze, to set it off. Nobel's detonator was a significant step forward in the development of modern explosives technology.
It is a liquid explosive and dangerously sensitive. In fact, it was so unsafe that it is astounding that anybody wanted to be anywhere near it, and Nobel's brother Emile was killed while working with it. It was often carelessly shipped as normal freight, without markings to indicate special handling, and terrible accidents occurred. Nitroglycerine was banned in several nations.
Late in the 1860s, workers found that nitroglycerine that had been frozen was almost impossible to detonate, and so manufacturers began to freeze it for shipment. However, this was clearly a stopgap solution.
Alfred Nobel was already working on ways to make a safer explosive. He determined that nitroglycerine was much less sensitive if it was absorbed in "diatomaceous earth", a porous clay that consisted of the deposits of the skeletons of tiny sea creatures laid down aeons before. This material could be packed into cardboard tubes and reliably transported, handled, and detonated. It could not be set off by a spark or a flame. It was not only safer than nitroglycerine, it was even safer than black powder.
Nobel named it "dynamite", and it quickly became the industrial explosive of choice. Dynamite offered much of the power of nitroglycerine with greatly improved safety. However, it was not perfect. The nitroglycerine in dynamite tends to "sweat out" in storage, and even form puddles in crates. Cold weather also tends to crystallize the nitroglycerine inside a stick of dynamite, making it more sensitive.
Another problem is that nitroglycerine causes dilation of blood vessels. As it can be absorbed through the skin, people who handle dynamite often have pounding headaches. Incidentally, because of this property, nitroglycerine is also used in small doses as a medicine for people with heart conditions.
The tendency of dynamite to become sensitive in storage made it dangerous to stockpile, and so military forces were not enthusiastic about it. Nobel managed to produce another nitroglycerine derivative named "blasting gelatin" that was more stable than dynamite, and could also be detonated underwater.
* Despite its limitations, dynamite remained the predominant commercial explosive until the 1950s, when "ammonium nitrate" explosives were began to become popular.
Ammonium nitrate (AN, with the chemical formula NH4NO3) is useful as an explosive when mixed with other combustible or explosive substances. In particular, a mixture of ammonium nitrate and diesel fuel known as "ammonium nitrate fuel oil (ANFO)" is commonly used as an industrial explosive. It is also well-known to makers of home-brewed explosives.
The fuel oil in ANFO provides a source of energy, while the ammonium nitrate provides oxygen for the fuel's combustion. However, the breakdown of ammonium nitrate itself produces energy, giving ANFO a hefty explosive kick. ANFO is much cheaper and less sensitive than dynamite, and does not give users headaches, at least not by simply laying hands on it.
In principle, home-brewed ANFO is synthesized by mixing diesel fuel and ammonium nitrate fertilizer together until the mix has he consistency of toothpaste. In practice, it's not that simple. Commercial fertilizer doesn't have the explosive potential of bomb-quality ammonium nitrate, for which access is carefully controlled, and a simple mix of fertilizer and diesel just burns and melts, rather than explodes.
To actually make an explosive out of fertilizer, aluminum, zinc, or potassium sulfate (K2SO4) have to be added to the mix as boosters. The amount of additive is critical. If too little is added, the mix won't explode, and if too much is added, it's liable to go off unpredictably. Synthesizing ANFO is not a job for the inept.
The potential danger of toying with ammonium nitrate was thoroughly demonstrated on 16 April 1947. A French freighter loaded with ammonium nitrate fertilizer was docked at Texas City, Texas, on the Gulf Coast. The ship caught on fire in the morning and attracted a crowd of spectators along the shoreline, who believed they were a safe distance away.
In mid-morning the ship exploded, killing hundreds with the tremendous blast, sending a tidal wave surging over the shoreline, and setting refineries on the waterfront on fire. A second ship loaded with fertilizer exploded after midnight, but emergency workers were given warning, they evacuated the vicinity of the vessel, and only two people were killed.
Fires burned for six days after the disaster. Official casualty estimates came to a total of 567, but many victims were burned to ashes or literally blown to bits, and the official total is believed to be an underestimate.
* Ammonium nitrate is also used as the basis for what are called "gelled slurry explosives (GSX)", which are generally used in mining applications. A typical formulation would ammonium nitrate and powdered aluminum mixed in water, with polystyrene powder added as a gelling agent. They form a mudlike mixture that can be pumped out holes drilled in hard rock, and have high brisage for shattering such rocks.
* Coal miners work in an environment full of flammable coal dust, making the use of any kind of true explosive dangerous. As a substitute, they use a "blasting charge" that consists of a cylinder full of liquified carbon dioxide and containing a heating element. The carbon dioxide expands rapidly when the heating element is activated, and bursts the container, producing a blast but no flames.
* As mentioned in the previous section, explosives like nitroglycerine, dynamite, and ANFO are not very well suited to combat use, though they all have been used in warfare to an extent. Different explosives have been developed for the battlefield and are widely used by military forces. Of course, military explosives are also used to an extent in commercial applications, but they are relatively expensive, and ANFO remains the bulk explosive of choice for civilian uses.
The ideal military explosive is powerful; easy to handle; can be stockpiled for long periods of time in any climate; and hard to detonate except under precisely specified conditions. It also has to be loaded into shells, bombs, and and the like, and so has to be meltable, so it can be poured into shells; or plastic, allowing it to be "extruded" into shells like caulk from a tube; or insensitive enough to allow it to be packed safely into the shell in bulk form.
* Military explosives have been improved for over a century and are now thoroughly refined. The first military high explosive to be put into service was "picric acid", a yellow crystalline substance with the chemical formula C6H3O7N3, which was first demonstrated by the French in 1885. However, picric acid has a high melting point, making the process of filling shells with it difficult; reacts with heavy metals to form toxic compounds; and tends to be sensitive.
The first modern military explosive was "trinitrotoluene (TNT)". TNT was first discovered in the 1860s, but was not put into service until the German military adopted it in 1902. It was widely used in World War I. It is relatively insensitive, and can be melted at low temperature to allow it to be poured into bombs and shells.
The British also used TNT during World War I, but after the war adopted a more powerful explosive named "Research Department Explosive (RDX)". RDX, more precisely known as "cyclotrimethylenetrinitramine" and sometimes called "cyclonite", was originally formulated in 1899. It has the insensitivity of TNT but greater explosive yield.
TNT and RDX are still the most important military explosives. Other military explosives include:
* In practice, most military explosives are mixtures of these explosives and other materials. For example:
Composition A is produced in several different formulations with the designations "A-1" through "A-5", though A-4 and A-5 are not widely used.
Similarly, Composition C has the formulations "C-1" through "C-4". C-4 is favored by the US Army for demolition charges, and filler in grenades and land mines.
New explosive materials are always being developed. One modern military explosive, "High Melting Point Explosive (HMX)" or "Octogen", is said to be about 75% more powerful than TNT, and is now in widespread use as a filler.
One particularly interesting new explosive is "octaninitrocubane". This experimental material is derived from "cubane", a hydrocarbon built around a cubical arrangement of carbon atoms that was synthesized in the 1960s. The cubical core of cubane makes it very dense, almost twice as dense as gasoline.
In the early 1980s, US Army researchers realized if cubane could be modified into a high explosive, its high density would permit faster propagation of breakdown reaction, leading to a more powerful explosive, as well as a more compact one. Octaninitrocubane consists of a cubic core of eight carbon atoms, with an NO2 group attached to each corner of the cube.
Although the new explosive has not been through full evaluation yet, researchers believe that it may be twice as powerful as TNT and very stable, and that its breakdown products will be non-toxic carbon and nitrogen compounds. It appears to be somewhat difficult to synthesize, however.
* Detonators have traditionally been made from "fulminate of mercury" or "lead azide". These are salts of "hydrazoic acid (HN3)", which is a dangerous and unstable liquid explosive, and have the respective formulas of Hg(N3)2, and Pb(N3)2.
Fulminate of mercury is highly unstable, and mercury is a relatively expensive material, not to mention a toxic heavy metal. For these reasons, fulminate of mercury is no longer widely used as a detonator. Lead azide has less yield but is more stable, and remains the material of choice for detonators.
* Black powder had been the only propellant available for firearms and artillery until the middle of the 19th century, when various chemists began to investigate treatments of paper, wood pulp, and particularly cotton with nitric acid (HNO3). These experiments resulted in "guncotton", which had promise as a propellant as it burned quickly and produced a large amount of gas. However, early formulations of guncotton were unsafe to produce and handle. It also burned too fast, and could cause firearms to blow up in the shooter's face.
Chemists finally managed to create stable formulations of guncotton through processing refinements with sulfuric acid (H2SO4), ether ((C2H5)2O), and alcohol (CH3OH or CH3CH2OH). The first form of smokeless powder to gain widespread acceptance was "Poudre B" or "B powder", synthesized in 1884 by a French chemist named Paul Vielle.
All such "smokeless" powders were based on nitrocellulose. Cellulose is a long-chain biopolymer found in plants, and treatment with nitric acid replaced hydroxyl groups (OH) on the chain with nitrate groups (NO3). The higher the percentage of hydroxyl groups replaced, the more powerful and sensitive the powder became. Creating a reliable smokeless powder required manipulating the percentage of nitrate groups through processing, and adding the appropriate moderators and other useful elements.
In the meantime, in 1875 Alfred Nobel created a smokeless powder named "ballistite", based on a combination of nitroglycerine and guncotton. This led to another smokeless powder, based on a mixture of guncotton, gelatinized nitroglycerine, and petroleum jelly, developed by Frederick Abel and James Dewar in 1889. The material was drawn out in a cord and so was named "cordite". Cordite was adopted by the British, who did not trust B powder, and by World War I cordite was the dominant propellant.
* Modern propellants are categorized as "single-base", "double-base", and "multi-base" or "composite" powders:
Firearms now generally use single-base or composite powders. Double-base powders are now generally used as a propellant for solid-fuel rockets.
Smokeless powders are not truly smokeless, but they burn much more cleanly than black powder. Burning rate of smokeless powders, as with other explosives, can be controlled by varying the size of the powder grains. Large grains burn relatively slowly, and so are appropriate for use in pistols and other weapons with short barrels. Grains can also be perforated so they burn from the inside as well as out.
* The military also makes heavy use of incendiary materials. Incendiary weapons have long been used in combat, for example, the "flaming arrows" used by Apaches to set wagons on fire in Western movies. In the 7th century AD, Byzantine Greek alchemists found that a mix of pitch, naphtha, sulfur, and petroleum would burst violently when ignited, and named the mixture "Greek Fire". The empire's military used it to defend Constantinople from invading Saracens. Later, in naval fighting during the age of sail, cannonballs were often heated red-hot before firing in hopes of setting an enemy vessel on ablaze.
Modern military incendiary munitions consist of "napalm", "fuel-air explosives (FAEs)", and metallic compositions. Napalm is simply gasoline to which a thickener has been added to make the burning fluid viscous and sticky. The original World War II form of napalm used a soapy thickener named "sodium palmitrate", leading to the name "na-palm". Modern "napalm B" uses polystyrene plastic beads as a thickener.
FAEs spray out an aerosol cloud of a hydrocarbon liquid such as ethylene, and then ignite it to create a flaming explosion over a wide area.
Aluminum has already been mentioned as an incendiary metal. Other incendiary
metals include zirconium, magnesium, titanium, and depleted uranium. They
all burn at very high temperatures. A particularly useful metallic
incendiary is "thermite", which is a mix of ferrous oxide (Fe2O3, essentially
rust) and aluminum. The thermite reaction is as shown below:
Fe2O3 + 2Al -> Al2O3 + 2Fe
One new scheme uses a "combustible foil" based on pyrotechnic metals to perform emergency welds. The foil contains thin alternating layers of metals such as nickel and aluminum. The foil is ignited by a match or a 9-volt battery, and instantly ignites over its entire surface. It works in a vacuum or underwater, and can be used by soldiers for emergency field repairs. The combustible foil could also be used for detonators and heating devices.
* White phosphorus was also once used as a military incendiary. Elemental phosphorus comes in two forms, a "red" amorphous form, and a "white" form arranged as tetrahedral units of four atoms. Red phosphorus is relatively easy to handle, but white phosphorus ignites spontaneously at room temperature. White phosphorus is now mainly used to generate smoke.
White phosphorus also serves a role in the most common pyrotechnic device, the safety match. The match was invented by an English chemist named John Walker in 1826, when he was mixing chemicals with a small stick and accidentally scraped the stick on a rough surface. It caught fire. Walker followed up the lucky accident by developing and selling the first matches.
The basic design of the match remains much the same as Walker' original invention. The head still consists of an oxidizer such as potassium chlorate (KClO3); a fuel such as sulfur or rosin; and a binder (glue). Modern safety matches, however, have a tip of phosphorus trisulfide (P4S3). The stem is dipped in a fireproofing agent to keep it from burning too easily, and the head is coated with paraffin to keep it dry.
The striking surface on the package of matches is coated with powdered glass and red phosphorus mixed in a binder. When a match is scratched over the striking surface, the red phosphorus in the surface is converted to white phosphorus by heat of friction, and the phosphorus trisulfide burns in the air. This ignites the fuel and oxidizer, which creates a sustained flame. The match will not easily ignite if scratched on any other abrasive surface.
* Other pyrotechnic materials are used as heating fuels, in fuzes or flares, to create smoke, fill up automotive airbags, or propel rockets. Some common pyrotechnic devices include:
Military aircraft often carry thermal flares to distract heat-seeking missiles. At first, ordinary signal flares were used in this role, but missiles became more sophisticated, and so flares became more sophisticated as well.
Modern decoy flares consist of Teflon plastic mixed with a fluorine compounds as an "oxidizer". They may contain two "stages" that burn at different temperatures at different times. The latest "pyrophoric" flares are made from ribbons of metal that oxidize at a rapid rate just short of burning in order to simulate the moderate temperatures of a jet exhaust. Missiles have become so smart that aircraft are now moving towards laser systems to confuse them, as flares are no longer up to the job.
This requirement led to the development in the 1970s of small, cheap, solid-propellant inflators, based on the combustion of "sodium azide (NaN3)" with an oxidizer, rapidly producing a great quantity of nitrogen gas that can inflate an airbag in a little over 50 milliseconds. Sodium azide consists of interlinked lattices of ions of sodium and azide, a group of three chemically bound nitrogen atoms. A shock disrupts the lattice structure, and the sodium combines with oxygen, while the nitrogen atoms regroup into pairs to form a large quantity of nitrogen gas.
After the war, this scheme evolved to modern solid rocket fuels based on certain forms of synthetic rubber, mixed with ammonium perchlorate oxidizer and a high concentration of aluminum powder. The synthetic rubber not only provided a fuel source, but also acted as a "binder" that could be cast in a huge solid block, without voids or cracks that would cause uneven combustion, that could be safely stored for a long period of time without degradation. Each solid-fuel booster on the space shuttle weighs 500 tonnes.
One interesting application of modern solid-rocket fuel is for mine disposal. Flares filled with solid-rocket fuel have been designed so they can be set up over a mine on little pop-out legs. The hot exhaust burns through the mine casing and sets the explosive filling on fire.
* While fireworks may not seem like high technology, they are a highly refined art. There are two basic schools for fireworks fabrication, the Oriental and the Italian. In the US, fireworks are manufactured by a few concerns, most of which run in Italian families, such as the Zambellis and the Gruccis.
Nearly all pyrotechnic materials except for high explosives are used in fireworks. The basic constituent of many fireworks is, as mentioned earlier, black powder, but flash powders and smoke-generating pyrotechnics are used as well.
Simple firecrackers and rockets are made from black powder in paper cases. Sparklers are made from a thick slurry consisting of fuels, binders, and oxidizers into which wires are dipped. Whistling fireworks use gas-generating pyrotechnics that are packed into narrow tubes that create the whistle when the gas escapes.
Roman candles consist of a set of bright "stars" that generate light and color, packed into a paper tube in layers of black powder. As the black powder burns down from the top of the tube, it ignites each layer of black powder in turn, spitting out a star.
The stars are made of mixes of pyrotechnic metals, salts, and binders such as resin and gum. Stars in oriental fireworks are rolled into shape, while Italian stars are generally made from cakes and cut into cubes. The round Oriental stars can have multiple layers, causing their appearance to change as they burn.
Early stars and other illuminating elements could only obtain white and gold effects, using saltpeter. Modern stars obtain a wide range of color effects using strontium compounds for reds; titanium, magnesium, or aluminum for whites; copper compounds for blue; barium compounds for greens; incandescent steel and charcoal particles for gold; and sodium compounds for yellows.
Clever chemistry has to be employed to get the desired results. The strontium and barium compounds aren't stable in storage, for example, and have to be synthesized through chemical reactions during the pyrotechnic process. Copper compounds will break down if the pyrotechnic process is too hot, destroying the color, so the firework has to be carefully designed to burn at a low temperature.
A "setpiece" is an obscure form of fireworks display that is undergoing something of a revival. It consists of hundreds of tubes of color-generating fireworks mounted on a wooden frame in a graphics pattern and linked with a fast-burning black powder fuse taped to the frame. The fuze sets off all the tubes quickly to generate a vivid display, and can also set off pinwheels and other fireworks attached to the display.
Large skyrockets are also used in public displays. They use a black powder propellant, sometimes mixed with other pyrotechnic materials so they leave a spectacular trail, and have a payload consisting of stars or other pyrotechnic elements dispersed by a black powder bursting charge.
However, the main firework for public spectaculars is the "shell". Shells can be built to produce a variety of effects:
Shells consist of a payload and a "lift charge" of black powder that lifts it into the sky. The shell is stuffed down a PVC pipe mounted in a sandbox, and lit off by an incendiary fuze or, more commonly in big fireworks displays, by an electric spark from a "squib". When the shell is fired, a time-delay fuze, or "spegette", inside the shell is lit, and burns down to set off a black-powder charge that bursts the shell and disperses the stars.
Oriental shells are spherical, while Italian shells are cylindrical. Bursting charges in Oriental shells may consist of rice hulls impregnated with black powder to increase the flash of the burst. Oriental shells are appropriate for generating symmetrical displays, such as chrysanthemums.
Italian shells burst in a more irregular fashion, but they can be designed with multiple firework stages or "breaks", connected by spegettes, that detonate consecutively. For example, a three-break Italian shell might consecutively disperse a burst of red, white, and blue stars.
Multiple-break shells can be very elaborate. The blast charge may ignite a set of stars so the shell's launch is suitably spectacular, and the stages may contain such elements as whistling pyrotechnics as well as stars.
Sophisticated fireworks displays often use elaborate control systems to sequence the ignition of fireworks, and synchronize them with sound and laser effects.
One of the more interesting fields in modern fireworks are indoor fireworks displays, produced by specialist firms such as Lunatech Indoor Fireworks of California. Such displays are used in rock concerts and other entertainments, and use conventional fireworks technology, modified with strict safety standards in mind to ensure no toxic emissions and appropriate safety for performers and audience.
* One interesting area of explosive technology are "tagging" systems that allow the identification of the origin of an explosive that was used, for example, in a terrorist bombing. While analysis of the chemical composition of blast residues can help identify the type of explosive, the ability to trace explosives by production batch is much more useful.
One explosives tagging technology has been around for several decades. Microtrace Incorporated of Blaine, Minnesota, markets a "MicroTag" scheme that was invented in the 1970s by a chemist at 3M Corporation named Richard Livesay.
3M developed and sold the MicroTag system, which is based on tiny chips, each about the size of a grain of pepper, that are built as a stack of up to 10 colored layers. A batch of chips with a particular "rainbow" code is mixed with a particular batch of explosives to permit its identification. A US government-mandated test of the tags that required their use in 1% of commercially produced explosives made from 1977 through 1979 demonstrated no real problems with the technology, and even led to the solution of one bombing. The Swiss, who were early adopters of the technology, have solved hundreds of bombing incidents through the use of the tags.
However, a disastrous accident at an explosives factory in 1979 was blamed on the tags, and led to a lawsuit against 3M. Though the company won the case, they got out of the taggant business, selling it to Livesay, who founded Microtrace. Most of Microtrace's customers use the MicroTags to protect goods, like shampoo and alcohol, from counterfeiters.
A subtler tagging technology is being marketed by Isotag LLC in Houston. The Isotag scheme is based on inert heavy molecules, uniquely keyed by selectively substituting deuterium (heavy hydrogen) atoms for ordinary hydrogen in the molecular structure. It has been used in applications such as identifying batches of petroleum sent through pipelines, and for tagging batches of ammonium nitrate.
* I am by no means an explosive enthusiast. This document evolved out of a longer writeup named DUMB BOMBS AND SMART MUNITIONS. An early version of DUMB BOMBS included a short survey of explosives, but it didn't seem to fit very well, so I removed it and merged it other interesting information I found on pyrotechnics and fireworks to create this document.
Of course a warning is required for a document on explosives. There's not much in the way of practical specifics in this document, so it's unlikely that anyone could use it to cause much trouble, but I would still suggest that taking advice on synthesizing explosives from somebody who's never done it and immediately admits he's no expert might be unwise.
* Writing this document brought back memories of my military tour of duty in the early 1970s. No one who was ever a soldier can forget watching a parachute flare floating down through the night, scattering its harsh white light over the landscape. When I was stationed at Fort Hood in Texas, I also occasionally saw flashes of light that lit up the sky, apparently due to photoflash flares dropped by reconnaissance aircraft over the range area.
The idea of the self-heating ration cans made during World War II was interesting. Although I have seen cheesy little camp stoves that used fuel pellets, I never saw a self-heating can, and why such a seemingly good idea was abandoned is an interesting question. In a pinch, a soldier could more or less heat up a can of C-rations by punching a hole in the box, sticking the can in the hole, and burning the box. It was usually better to sit the can on the muffler pipe of a generator, though this could lead to messy consequences if it was forgotten.
Modern MRE military rations, so I have heard, include a pyrotechnic cardboard "sandwich" that gets hot when doused with water, and transmits the heat to the meal through a matrix of staples driven through the cardboard.
I was in the Signal Corps and never played much with weapons beyond my M-16, but heard interesting stories about C-4 and detcord. C-4, I was told, could be burned, but it was sensitive to shock, and stepping on it to put it out was dangerous. I heard some stories about some of the nasty things that could be done with it, but won't repeat them here for fear of giving people bad ideas.
People who used detcord compare it to "waxy closeline cord" and say it was a remarkably flexible tool. For example, detcord could be used to cut a 55-gallon fuel drum in half, to use in a latrine or whatever, simply by wrapping a length of detcord around it and detonating it. It is also used in aircraft escape systems, for example to shatter a canopy before firing an ejection seat. Shattering the canopy is faster and more reliable than blowing it off, and aircrew will not collide with the canopy on ejection.
* Sources for this document include:
Other information was obtained from various encyclopedias, and interestingly the Microsoft ENCARTA on-line encyclopedia has some nice, well-organized little writeups on explosives and pyrotechnics. I also found some information in TV shows on explosives and fireworks broadcast on the HISTORY CHANNEL and the DISCOVERY CHANNEL.
I picked up various small items by surfing the Web, but as far as I know this is the only comprehensive document on the subject on the Internet. That's a shame as I would certainly like to get a few more reality checks from people with professional experience.
* Revision history:
v1.0 / 01 dec 99 / gvg
v1.1 / 01 mar 01 / gvg / Cosmetic rewrite, minor additions.
v1.0.2 / 01 jul 02 / gvg / Cosmetic rewrite, minor changes.