Pyrotechnics

Summary

Pyrotechnics is the science of controlling exothermic chemical reactions, using materials that are self-contained and self-sustained to produce gas, heat, light, sound, and smoke. These types of exothermic chemical reactions have been developed in a variety of ways: to provide entertainment, promote safety, and generate compounds such as oxygen. Such reactions are used, for example, in fireworks, military ordnance, automotive airbags, chemical oxygen generators, pyrotechnic fasteners, and safety matches. Reactions can be carefully controlled and timed to automate remote actions or effect precisely timed sequences, such as those used in spaceflight. Those who study and practice in this field are called pyrotechnicians.

Definition and Basic Principles

The ever-changing field of pyrotechnics encompasses a broad range of exothermic chemical reactions that scientists and inventors have put to many uses. To the ordinary observer, the most visible use of an exothermic chemical reaction is that of fireworks for entertainment. However, this field has also been applied in many other areas, particularly to promote safety in air travel, spaceflight, mining, and firefighting.

This field of pyrotechnics does not include endothermic reactions, those that need energy to take place, such as an ice cube melting or a liquid evaporating. It also does not include anything related to the concept of “fire” in general, that is, in the sense of lighting things on fire.

Background and History

Fireworks are said to have originated in China more than 2,000 years ago. The story is a cook mixed charcoal, sulfur, and saltpeter (all materials commonly found in kitchens thousands of years ago) in a bamboo tube. When the tube filled with these substances got too close to a fire, it exploded. A Chinese monk, Li Tian, then took this explosive mixture a step further. He attempted to find ways of controlling the explosion, thus creating firecrackers. Li Tian lived in Liu Yang, in the Hunan province of China, which is still a main center for the production of fireworks that are shipped around the world. Lighting firecrackers became a common event around holidays such as Chinese New Year, as ghosts and evil spirits were thought to be frightened away by the loud noises of firecrackers. These exploding devices are still used at events marking births, deaths, and the New Year in Asia, as well as other holidays celebrated around the world, including American Independence Day.

The explorer Marco Polo is believed to have brought the recipe for gunpowder—the combination of charcoal, sulfur, and saltpeter created by the Chinese cook—back to Europe after visiting China in the thirteenth century. The Crusaders, who traveled from Europe to the Holy Land (modern Israel and Palestine) to fight Muslims and establish Christian rule, may also have been familiar with gunpowder after their trips to the Islamic world. Europeans began to use gunpowder for military purposes, but Italy was the first country where gunpowder was used to manufacture fireworks for display and entertainment. The Germans followed, and then the English, who developed fireworks and took them to new heights. Queen Elizabeth I created a highly regarded position in her royal court called the Fire Master of England, and King James II knighted his Fire Master for developing a brilliant fireworks display that celebrated James's coronation. William Shakespeare mentions fireworks in his writings, and George Frideric Handel is famous for composing music for the royal fireworks for King George II.

As scientists explored the chemical reactions occurring when certain substances were combined, they began to find uses for them beyond their entertainment value. For example, Swedish scientist Johan Edvard Lundström used this type of chemical reaction in his patent for safety matches in 1855. He put red phosphorus in sandpaper on the outside of a matchbox and the rest of the ingredients necessary to complete the chemical reaction he was seeking on the match heads inside the box. These special matches lit only when struck on the phosphorus-loaded sandpaper surface. These reactions were further studied and developed by scientists and inventors to bring about safety devices such as chemical oxygen generators and automotive airbags and controlled explosions such as those used in pyrotechnic fasteners.

How It Works

Pyrotechnics relies on exothermic chemical reactions, those that release heat or energy. A common example of an exothermic chemical reaction is fire. However, there are many other examples, such as the release of oxygen on demand, using a controlled chemical reaction other than fire. Controlled explosions that work underwater or in remote areas are another type of exothermic chemical reaction, representative of the field of pyrotechnics.

Fireworks. The way pyrotechnics works can be detailed by the familiar use of fireworks. Fireworks consist of a shell composed of four parts: a container (a cylinder of paper and string), stars (balls made of a sparkler-type substance about the size of a pea), the bursting charge (similar to a firecracker), and a time-delayed fuse (to ensure the shell is at the correct height before exploding). The stars are packed into the container with, generally, a tube full of bursting charge through the center and more bursting charge (a gunpowder-like substance) sprinkled throughout. This shell is launched from a mortar (usually a short steel pipe) by a lifting charge exploding into the tube, where nitrogen and carbon dioxide expand and fling the firework into the sky. This lifting charge also lights the shell's fuse, which burns slowly until the shell reaches a safe altitude. It is also possible, but not as common, to use compressed air to launch fireworks and an electronic timer to detonate the charge.

These shells can be arranged as “multi-break shells,” which explode in phases, similar to a two-stage rocket, and possibly contain stars of different types or colors. They may also contain noisemakers such as whistles. Each of these shells has a different time-delayed fuse that lights it so each shell can explode with, for example, brighter light or more sparks than the one before. These multi-break shells can be burst apart to explode farther away from each other and create designs by break charges (small explosive charges). The patterns created depend on the placement of the stars in the shell and the timing of the break charges that ignite them. For example, to create a heart pattern, the shell would be packed with stars in a heart shape, and then a break charge would be tied to this group of stars to separate them all from the main shell at the same time.

Fireworks get color from basic chemical elements as they burn. Common colors produced are blue (copper), green (barium), red (strontium), white (magnesium), and yellow (sodium). Some of these elements are unstable and must be combined with other ingredients to maintain stability.

Chemical Oxygen Generators. A typical chemical oxygen generator contains a mix of sodium chlorate and iron powder. When this mixture is ignited, either by an automatic or manual switch, it smolders, releasing sodium chloride, iron oxide, and oxygen at a fixed rate through thermal decomposition. The most familiar type of chemical oxygen generator is that used on a commercial airliner. If the cabin of the airplane becomes decompressed, panels containing oxygen masks connected to a chemical oxygen generator open. When passengers pull on the mask, the retaining pins fall away and ignite the mixture, releasing oxygen.

Applications and Products

Fireworks. Fireworks, a class of low-explosive pyrotechnics, are an integral part of many cultural, religious, and patriotic celebrations around the world. They range from small devices that can be used by one person or a small group, such as firecrackers, to large displays for hundreds of people. They produce four primary effects: light, noise, smoke, and the dispersal of floating materials, such as confetti. They can be designed to burn in many colors, including red, orange, yellow, green, blue, purple, and silver. They are generally classified as either ground or aerial fireworks. Aerial fireworks may be skyrockets, which have their own propulsion system, or they may be designed using mortar shells and are shot into the air, where they explode. Fireworks are usually created using a pasteboard casing filled with some type of combustible material. Many casings are combined with different types of materials and colors to create shapes when exploded. In 2021, the American Pyrotechnics Association (APA) reported that professional fireworks displays accounted for $262 million in revenue. This figure was likely held down by some continuing restrictions from the COVID-19 pandemic that began in 2020. Figures from 2019, the year before the pandemic, show a record $375 million in revenue. Fireworks sales continued to rise as the 2020s progressed. The APA reported over $2 billion in sales in 2023.

Safety Matches. Safety matches are used just about everywhere. Their ability to keep from spontaneously igniting makes them useful in safely lighting fires, such as those in fireplaces or barbecues. These matches are produced in such a way that they must be struck against a particular surface, setting off a chemical reaction that allows them to ignite. A safety match head contains sulfur and an oxidizing agent such as potassium chlorate. Other ingredients, such as powdered glass, color, and a binder made of glue and starch, keep the match head together until it is struck. The surface upon which the match must be struck may be powdered glass or sand and red phosphorus. The glass struck against glass generates heat that converts the red phosphorus to white phosphorus, a vapor that spontaneously ignites. This ignition liberates oxygen and causes the sulfur to burn and ignite the wood of the matchstick.

Chemical Oxygen Generators. Also known as oxygen candles, these generators hold a chemical reserve of oxygen that is released through an exothermic chemical reaction. They are used in places such as airplanes, mines, submarines, or the space station to hold a large amount of stored oxygen in a small space and in a lightweight form. For example, a chemical oxygen generator weighing about 40 pounds can provide about four days of oxygen. This type of generator usually contains a sodium chlorate pellet (but may contain inorganic superoxide or perchlorate) and an igniter, such as a firing pin, which is activated by a pull tab. This igniter can be triggered in a pyrotechnic reaction activated by friction or impact. Sodium chlorate gives up its oxygen as easily as almost pure oxygen when heated in a chemical reaction. As it decomposes (it does not truly burn), oxygen is released. This oxygen can then be used as a rescue inhaler, such as in a mining or firefighting situation, or be mixed with other gases to create an air-like environment in places such as a space station or submarine.

Explosive Bolts and Fasteners. A pyrotechnic fastener is another term for an explosive bolt. This type of fastener may be a nut-and-bolt combination or any other type of fastener. It is made to be broken and incorporates a type of pyrotechnic charge that is detonated remotely. These kinds of fasteners are used in places where it is extremely important that the break occurs at a certain predetermined time and place. An explosive bolt or nut is usually scored around the place where it needs to break. These kinds of breakable fasteners are used in the space shuttle, where a charge directed at the nuts around the bolts holding the space shuttle to the pad is detonated to release it at a certain point during the countdown. They are also used for separation during rocket stages. This type of fastener is more reliable than mechanical types of fasteners and is often lighter in weight and easier to control. Some typical chemical combinations used for this type of explosive are manganese, barium chromate, and lead chromate, or boron and potassium nitrate. The type of chemicals used depends on the amount of energy required to sever the connection and the burn rate desired. The detonator may be a blasting cap, though now it is possible to detonate with pulsed laser diodes and fiber-optic cables.

Automotive Airbags. Engineers who developed airbags for automobiles had considered the idea for quite some time. However, it was not until small solid-propellant inflators were developed in the 1970s that these types of safety devices became a real possibility. These inflators allowed a chemical reaction (sodium azide reacting with potassium nitrate) that produced nitrogen gas to inflate the bag. The nitrogen gas explodes in hot blasts to inflate an airbag at up to 200 miles per hour, then quickly dissipates through small holes, deflating the bag. The whole process takes place in one-twenty-fifth of one second.

Careers and Course Work

Two types of jobs in the pyrotechnic field are pyrotechnic engineers and pyrotechnicians. Pyrotechnic engineers design and create the explosions used in fireworks manufacture. They have a comprehensive understanding of the chemistry and physics used to craft a chemical reaction that is safe and aesthetically pleasing as well as training specific to creating fireworks. Pyrotechnic engineers may also work at developing pyrotechnic fasteners or automotive airbags.

A pyrotechnician is someone who organizes and sets off the fireworks at a performance. These individuals have a specific knowledge of safety rules and regulations as well as governmental requirements for this type of show. A certified display operator certificate is often required for anyone performing in the fireworks field.

Many possibilities for employment in this field exist outside of the fireworks industry. Pyrotechnicians work in the field of rocketry, building and testing safe ways to detonate the type of explosions that are needed to launch rockets safely. Other possibilities include the safety field, which includes making and improving airbags for the auto industry and improving chemical oxygen generators for the auto, mining, and aircraft industries. Another possible field is that of special effects for television and movies, where one develops pyrotechnic displays or explosions that are safe for actors while the cameras roll. The military is another possible field for a pyrotechnician. Safe, controlled explosions that give military personnel an opportunity to experience them firsthand are necessary for training purposes.

Social Context and Future Prospects

Safety matches, fireworks, oxygen generators, and automotive airbags are part of everyday life; however, people do not often stop to think about the chemical reactions that make these possible. Though safety matches have not changed for many years, new and more efficient ways to generate a safe chemical reaction are worth investigating. Fireworks are a constantly changing field, and those who can engineer or deploy fireworks are always in demand. Engineers who can design interesting and beautiful displays are challenged in this field. Deployments of pyrotechnics in the military field are changing as well, and those who can develop and improve safe ways to deploy ordnance are in demand. Scientists, engineers, and researchers are constantly changing the way chemical oxygen generators are made and used to improve safety. New methods of igniting or beginning the chemical reaction in a safe way are being investigated, and new or different chemicals that combine to release oxygen easily can be found.

Auto airbags also continue to evolve. In the beginning, most of the attention was focused on front and rear impacts, even though 40 percent of serious injuries resulted from side impacts. Many cars now offer side airbags, though the engineering is difficult. Head airbags are another type of airbag that is optionally provided in some vehicles. Different ways of installing and triggering these types of bags are being researched to improve safety in the future. Though pyrotechnic fasteners are not generally part of one's everyday life, for those in the rocketry or underwater construction field, engineering to make these chemical reactions safer and more effective is always welcome.

As advances continued to be made in the pyrotechnic field throughout the twenty-first century, safety and environmental concerns were at the forefront of the field. Advances in manufacturing techniques and ignition technology led to safer products. Further, the environmental impact of pyrotechnics became a major concern. Green pyrotechnics and environmentally friendly firework technologies became more of the norm.

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