9 Things You Probably Don’t Know about Fireworks

The Fourth of July is almost here. But did you know that the development of firework shows requires an understanding of science, chemistry, physics, and engineering?
  • As an engineer, one of the worst things that can happen is if your product blows up. If you are a fireworks designer, however, your best end result is a spectacular explosion. It is generally agreed that the Chinese invented fireworks shortly after inventing gunpowder more than a thousand years ago. Today, the majority of fireworks come from China, although a surprising number of manufacturers are located in the US.

    It is also surprising how much engineering and technology goes into creating a commercial fireworks display. So this Independence Day, as you and your family enjoy the spectacle of aerial explosions and starbursts, give a moment’s thought to the engineers and technicians who make it all possible.

    Here are some interesting technical tidbits to help you understand the science behind the boom.

    Senior Editor Kevin Clemens has been writing about energy, automotive, and transportation topics for more than 30 years. He has masters degrees in Materials Engineering and Environmental Education and a doctorate degree in Mechanical Engineering, specializing in aerodynamics. He has set several world land speed records on electric motorcycles that he built in his workshop.

    (Image source: US Department of Defense)

  • SOFTWARE AND SIMULATIONS

    Building a professional fireworks show takes a lot of planning—much of which is done using computers and simulation programs. Choreography using a software tool from Finale Fireworks or one from ShowSim allows designers to preview their creations without the explosives ever leaving the ground. Interactive 3D perspectives also let the creative developers view the show from different audience viewpoints.

    Prior to the invention of “e-match,” the pyrotechnics were fired by hand using manual switch panels. But now, once the show has been fully programmed, script files can be exported to the firing system to make sure that each launch and explosion is timed to perfection. Better and safer shows are the result.

    (Image source: ShowSim)

  • PATTERNS

    The shell is a container, usually made of paper and formed into a cylinder. A simple shell that explodes into stars might be pieces of sparkler compound, each about the size of a pea. The stars are poured into the paper tube and then surrounded by black powder of the bursting charge. A fuse is lit as the shell is launched. And when it burns into the shell, it ignites the black powder, causing the shell to explode. At the same time, the sparkler compound is ignited and the sky is filled with a shower of brightly burning stars.

    More complicated shells can be made with different sections containing varied colors and star effects that burst in two or three different phases. Different sections of the shell can be ignited at different times using separate fuses.

    To create a pattern, the outline of a figure can be done with star pellets that can then be blown apart with explosive charges to make the figure grow larger. Timing is obviously critical or the figure won’t grow properly.

    (Image source: American Pyrotechnic Association)

  • LAUNCHING

    The shell is launched from a short steel pipe called a mortar. A lifting charge of black powder explodes in the pipe and pushes the shell outward at great speed. The lifting charge also usually lights the shell fuse, which burns while the shell is rising to the correct altitude for the bursting charge to blow the shell apart. The launch speed of a firework can be as high as 150 mph and the altitude can be as high as 1,000 feet above the ground. The largest shells can be two to three feet in diameter.

    Rockets can also be used to launch shells into the sky. The simplest version is probably the bottle rocket, where igniting the fuse causes the propellant to burn, pushing hot gases out of the nozzle and propelling the rocket forward (see Newton’s Third Law of Motion). Simple bottle rockets can travel as high as 50-75 feet into the air. Sometimes, larger rockets are used to launch commercial shells. However, the cost can be significantly higher than the mortar system that is in more general use.

    (Image source: Skylighter)

  • CONTROLLED BY PHYSICS

    Calculating the trajectory for a fireworks projectile launched from a mortar tube is a straightforward two-dimension kinematics problem. In this case, the initial launch velocity is positive, the acceleration due to gravity is negative, and the maximum altitude depends only upon the vertical component of the initial velocity (neglecting air resistance on the shell). The horizontal velocity (moving downrange) is a constant (neglecting air resistance) and the position depends upon the time of flight.

    (Image source: study.com)

  • COLORS

    The bright colors that occur during a fireworks display are the result of the combustion of metal salts. Commonly used are strontium carbonate (red), calcium chloride (orange), sodium nitrate (yellow), barium chloride (green), and copper chloride (blue). The materials have to be chosen carefully, avoiding ones like sodium chloride (table salt) that absorb water and would produce a fizzle rather than a sizzle. We may like the brightest reds and yellows, but firework designers say it is actually pure white (often coming from burning magnesium)  and dark blues that give them the most trouble.

    (Image souce: sciencenotes.org)

  • DANGEROUS REDS

    The brilliant red color that is a favorite among fireworks aficionados has a dark side. The red hue comes primarily from strontium monochloride, which comes from burning strontium compounds with polyvinyl chloride and a range of other pyrotechnic compounds. But the combustion of this mixture also produces a variety of polychlorinated aromatic compounds, most of which are highly carcinogenic. The cancer causing chemicals fall back to earth after the oohs and ahhs are over.

    Looking for an environmentally friendly way to produce the red, researchers have found that they can replace the polyvinyl chloride compound with a citrus preservative (hexamine) or a material used in airbag propellants. This removes the cancer-causing chlorine and results in a relatively compound, strontium monohydroxide that produces bright reds while avoiding the production of strontium oxide, which has a less pleasing orange color.

    (Image source: Fireworks International)

  • COSTS FOR FIREWORKS

    With more than 14,000 fireworks displays across the US every July 4th, commercial fireworks are big business. A large-scale event that incorporates music and large-sized shells can cost about $2,000 per minute. Typical municipal shows range from $5,000 to $30,000 or more—sometimes much more. Some of the largest shows in New York City, Washington, D.C., and Philadelphia set off more than a thousand shells and can cost in excess of $6 million. According to the American Pyrotechnics Association, 2016 revenue for display fireworks was $332 million in the US.

    The world’s largest fireworks display is said to be the 2012 golden jubilee anniversary of Kuwait’s constitution. The display lasted for more than an hour and is reported to have cost over $15 million.

    (Image source: Jakes Fireworks)

  • INJURIES

    Setting off commercial fireworks is a job that is not to be taken lightly. Although injuries are fairly rare, they can include burns, eye and hand injuries, and even death. A larger risk comes from pieces of burning firework landing on a building or in a field and starting a fire.

    Injuries in the factories that make fireworks can be deadly. In 2017, seven people were killed in the Pingxiang, Jiangxi province in China in a factory explosion.

    Consumer fireworks—the kind that seem to flood your neighborhood on the 4th of July and New Year’s Eve—are much more dangerous. In 2016, for example, there were 11,000 fireworks-related injuries between June 16 and July 18. There were also four deaths related to fireworks in the US in 2016.

    Consumer fireworks are not legal in every state and are banned outright in Massachusetts. The American Pyrotechnic Association maintains a list of the rules for each state.

    Be careful and be smart—you don’t want to add to this year’s injury statistics!

    (Image source: Consumer Products Safety Commission)

  • MANUFACTURING

    There are 2,800 fireworks factories in China. It is one of China’s oldest industries, dating back more than 1,000 years. Recently, licensing of fireworks factories in China has become more stringent as worker safety has become an issue. There are 407 fireworks manufacturers in the US.

    (Image source: Red Moon Fireworks)

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