The Fourth of July is a time for inspiring fireworks shows.
But amid the booms and bombast, there are varying levels of chemistry and physics many don’t think about. Here’s more about the science behind fireworks.
The inner workings of a firework are the backbone of the evening spectacle. The inside of the shell is packed with black powder and small objects called stars, said Ric Almendinger, chief executive officer and owner of Big Sky Fireworks.
Stars are filled with chemical compounds that burn a certain color. Early renditions of fireworks didn’t have very many color options, but pyrotechnic techniques have introduced the use of metal salts for bright hues.
Red fireworks, for example, are made with strontium salts, while colors like blue use copper compounds. The metal salt is the base used for color but there is also a fuel inside to ignite and burn the star. Additionally, a chlorine compound is present to help strengthen the color, a spokeswoman for Zambelli Fireworks said.
Some fireworks only need one metal for the elegant color, such as orange using calcium compounds, yellow using sodium compounds and green using barium compounds. Purple, on the other hand, uses a combination of copper and strontium.
The designs that light up the sky are dictated by the stars inside the shell, Almendinger explained. After the black powder has been placed inside, the stars will be arranged in a specific design.
“Say you have red stars; you place them in a heart shape in the shell.” he said. “It might go the right direction, it might not, but it should look somewhat like heart. It depends on the angle that person happens to be sitting.”
Shells also incorporate filaments like string and paper. These objects will combine with the stars and cause effects after the explosion in the air. Depending on the filament, the explosion can have a falling effect or look similar to a raining motion, Almendinger said.
None of the chemistry matters if the firework hasn’t taken off. Physics and propulsion are critical to viewing the explosions in the air.
Fireworks incorporate a two-fuse ignition system. The two fuses allow the shell to take off and detonate in the sky.
“The shell is dropped into the mortar tube, the fuse is lit which burns to the primary ignition, which is called the lift charge,” the Zambelli Fireworks spokeswoman said. “The fuse lights the primary and secondary ignitions at the same time but the lift charge fires first. The timed fuses in the shell allow the second ignition to fire once it reaches the highest point.”
The size of the shell impacts how it will fly and how high it can travel. The mortar tube and amount of black powder inside the shell also affect the take off.
“The rule of thumb is 100 feet per one inch. So, a 3-inch shell will go up 300 feet,” Almendinger said. “If it’s 100 feet per inch, it’s also one second per inch. So, if you have a 3-inch shell, you want a three second delay to reach that 300-foot mark.”
Almendinger’s example for new workers is if a shell is 5-inches, it will reach 500 feet in five seconds. That means the shell is leaving the mortar tube at roughly 128 mph.
If a shell is made correctly, it will reach the 500-foot mark, slow down to 0 mph and then burst.
The direction a shell flies is completely dependent on the mortar tube. Almendinger said crews “can angle them or shoot them straight up.” Since firework shells are round, the lift charge is the power that deploys it into the air.
A shell can’t make it to the air if there is a lack of black powder inside. Almendinger explained that most fireworks are made in China and they have tools to ensure the proper amount is inserted into the shell.
“It needs to be preciously measured and taken seriously,” Almendinger said. “You can’t be like, ‘Oh that looks like enough.’ It needs to be calculated out.”
The larger the shell, the more powder it will need. If a shell is lacking the correct amount of powder, it won’t travel the proper height, in turn creating unsafe conditions for the crew.
Big Sky Fireworks takes safety very seriously when conducting shows, the company says. The company employs local residents, but training is still required. They have a rookie program to teach all the basics.
Almendinger believes it’s better to have no experience and be able to adapt and learn how the company works. The training also helps new workers learn to operate fireworks safely and correctly.
Big Sky always likes having new people come and help, but there is a routine to go through, according to Almendinger.
“The one thing we won’t do as a company is become complacent,” Almendinger said. “You start cutting corners or you don’t refresh or retrain, you don’t remind folks of the little safety things that we do, you might forget those things the next year. The last thing we want is an accident.”
First-time employees will only assist in prepping locations and focus on the hands-on labor. The company won’t allow new members to handle shells until the company feels comfortable with the person’s abilities, according to Almendinger.
They also encourage former workers to retake the rookie program to refresh their skills when the holiday comes around.
Anyone who has an interest in pyrotechnics is welcome to apply for a job. However, the position comes with responsibility and ability to perform.
“Is your mind and heart in the right place? Are you getting into fireworks to blow stuff up or to entertain? These fireworks aren’t made to impress your friends. They are professional equipment,” Almendinger said.
Additionally, there is an industry-standard federal background check that is conducted through the Bureau of Alcohol, Tobacco, Firearms and Explosives.
The firework festival in Casper is Thursday at the Casper Events Center. Activities begin at 4 p.m. and conclude at 11 p.m. There is an entry fee—$10 per carload and $5 for bikes, motorcycles and people on foot.