HISTORY - University of Alaska Fairbanks

HISTORY - University of Alaska Fairbanks HISTORY thAfter black powder was discovered by the Chinese in the 9 Century, the relatively short history of fireworks began with this explosive chemical composition. Black powder is made up of potassium nitrate, sulfur, and charcoal (KNO); in the correct amounts, this 3 combination has very explosive results. The use of black powder sprung forth the evolution of muskets, rockets, and fireworks. Although history has shown that the development of black powder muskets into modern day guns, artillery, and weapons of mass destruction have changed the face of the earth, taken many lives, and changed the outcome of many wars, black powder is also used in many rituals and celebrations. While traveling the globe, Marco Polo, fascinated by this black powder, brought it back to the West were it soon caught on. In Rome, King Charles V used fireworks to celebrate a victory. The fireworks were developed and made by his “fire workers” who made leaps and bounds with the projectiles and rocket shape of the fireworks. These elaborate demonstrations of fire soon spread through Europe and pleased many spectators of the King and Queens Court. In the middle ages, Italy and Germany took their displays to another level, incorporating different colors and effects. In Italy, the firework displays were used to accentuation buildings and structures, while in Germany, the focus was more on the fireworks themselves. The name "green men" was coined on account of the people who would cover themselves in leaves to protect their body from sparks and ashes as they launched fireworks from their hands. As music grew and became a large part of society, the incorporation of music and firework displays became inseparable. The most infamous of all fireworks displays, for this time period, was held by England in celebration of the peace treaty that ended the war of Austrian succession. This one thousand firework display was the biggest of its time; however, disastrous outcomes of this collaboration claimed the lives of two people and set fire to one females dress as the demonstration exploded before the show even started. Ironically, this catastrophic set-up was used as a model for the 1981 commemoration of the marriage between Prince Charles and Lady Diana Spencer. As music and fireworks progressed, the synchronized union between the fireworks display and a soundtrack was established. The French were the first to coordinate this masterpiece in Cannes, 1960. Today, fireworks are a multimillion dollar industry, producing over one million large ordinance fireworks per year. With modern technology, live video feed of demonstrations around the world link one unique display to the next. With the push to be the most original and unique, the future of firework displays are uncharted. The colors and effects most often seen today are inventions of this century. A major example is the development of colored displays. Before the 19th century, only various yellows and oranges could be produced with steel and charcoal. Basic reds and greens were added to the displays with the invention of chlorates along with good blues and purples late this century. PHYSICS The physics behind every large ordinance fireworks show is very involved and can range from vectors, velocities, trajectories, projectiles, and the directed force explosions from the shell. All these concepts and relationships are explored throughout the following page. The large ordinances, or aerial shells, are the only ones being explored in this section. The same concepts apply to the smaller fireworks, such as bottle rockets and Blackcats?. Initial Shell Velocities Aerial shells are the type of firework that is used at most Shell Size Initial Velocity Fourth of July celebrations. These shells range from the 2” salutes to the enormous 36” shells. There are different (in inches) (in ft/sec) combinations of aerial shells used during a display, the most 2" 117.5 common are the two-break color and report shell, the American cylinder shell, and the Oriental style shell. After 3" 144 the shell has reached its designated altitude, a burst of 4" 166 chemicals ignite to produce the brilliant flash of colored 5" 186 light. The projectile is launched from steel or more recently PVC tubes (mortars). 6" 203.5 he table to the right lists all commonly used shell sizes and T8" 235 their corresponding initial mortar velocities. The initial 10" 263 velocity of the shell is the speed at which the shell leaves the mortar. A typical show will use the 2" shells as salutes 12" 287.5 before the show starts. These shells usually don?t have any 24" 393 special effect except for the loud “bang” to suggest the start 36" 481 of the show. The most common shells used at a small fireworks display are below the 6" shell size. One could think of the price as being proportional to the size of the aerial shell, of course, the more intricate design and display from the firework itself, the more expensive. The expensive 8", 10", and 12" shell sizes are usually used at only large fireworks shows. The 24" and 36" shell sizes are the most expensive due to large burst patterns, materials, and production. The oversized aerial shells are rarely used due to the large hazards, cost, and scarcity of the shell. The table also shows that the larger the shell sizes, the greater the initial mortar velocities. This is an interesting relationship, one would think that the larger mortars would be slower out of the tube due to size and weight; this is actually the opposite of what 2happens. As the shell diameter increases, the area increases by r and therefore more room is allocated for the propellant. As larger amounts of propellant are burned, excess gas is produced and creates the lifting force. This force is greater as the excess gas increases. These larger amounts of excess gases cause the shell to be pushed or propelled out of the mortar faster, resulting in a faster initial velocity. The higher the initial velocity the more altitude the shell can attain before it explodes and emits its bright flash of light and pattern. These aerial shells usually travel ~100 feet vertically for every inch in diameter for small angles of θ from the vertical angle. The kinematics equations of motion can be used to demonstrate the relationship between the initial velocities and the distances traveled by the shell. 2y = vt + ?gt y where y is the displacement in the y direction, v is the initial velocity in the y direction, t y is time, and g is the acceleration due to gravity x = vt x where x is the displacement in x direction, v is the initial velocity in the x direction, and t x is time CHEMISTRY In the late 1830s, the Italians made a big breakthrough in pyrotechnic chemistry. They began adding the compound potassium chlorate to the traditional black powder mixture. The compound helped oxidize the reaction, enabling it to burn hotter and brighter. The strongly exothermic (heat-giving) reaction made additional reactions involving other compounds possible. A better understanding of how the brilliant hues of fireworks are created can be seen on an atomic level. Electrons orbit an atom?s nucleus in a “cloud” and can be found in different levels called orbitals. Electrons can be raised to higher-energy orbitals when an atom absorbs energy. The electrons then return to their original orbitals as the atom emits the absorbed energy as light. The atoms of different chemical elements release very specific wavelengths of light corresponding to the different colors that we see. Colors at the warm (red and orange) end of the spectrum correspond to longer wavelengths of light. Colors at the cool (purple and blue) end of the spectrum have shorter wavelengths. The most impressive colors come from the explosion of salts of certain metals, such as barium, strontium, and copper. Barium salts emit wavelengths of bright green light, while strontium salts glow a fiery red. Copper salts create different shades of blue and purple. The addition of sodium ions produces luminous golds and yellows. Wavelengths Color Element (in nanometers) Copper 420 - 460 nm (in copper salts) Barium 505 - 535 nm (in barium salts) Sodium ions 589 nm Strontium 636 - 688 nm (in strontium salts) These days, other metals are added for brightness or special effects. For example, aluminum and magnesium are added to make electrifying white light. Titanium adds sparks and a mighty kaboom, while Zinc helps create dreamy smoke clouds. CONSTRUCTION The construction of aerial shells is crucial to the success of the fireworks display. Each shell is made in a controlled environment, taking all the necessary steps for safety and the prevention of a large scale disaster. DO NOT TRY THIS AT HOME! The construction of aerial shells that produce the large star effects are fired from ground mortars. The construction of the shell must be consistent and accurate. If a shell gets stuck in a mortar tube and never leaves the ground, a potential mass explosion could cause a chain reaction with the near by shells. If a shell is out of balance or the lifting charge is inadequate, the shell could stray from the desired trajectory and, again, cause a safety hazard. The construction of the Oriental style shell and the American cylinder shell has been perfected over the past 30 years. These two shell designs are the primary style constructed and used world wide. The Oriental sphere shells are similar to the small 1” shells that can be purchase at any good Fireworks stand. The American cylinder shell can be thought of as a large bottle-rocket without the shaft. The basic components of a shell consist of a lifting charge, time fuse, burst charge, and effects/stars. Also, the 2-Break and Report shell is a variant of the American cylinder shell (common). The first step in creating an Oriental style shell is to make a spherical form. Then place a thin layer of plastic in the form so the shell paper does not get stuck when the process is complete. Next, apply the shell material around to the form; most commonly used is newspaper. This step can be thought of as paper mache to create the shape and exterior shell wall. The larger the shell, the more layers of newspaper required. Heat shell and form in oven for about three hours or until completely dry. Cut shell in half; must be exact. The shell can now be loaded with the burst stars and pasted back together for firing. The lifting charge is then created and pasted to the bottom of the shell. DO NOT TRY THIS AT HOME! Below are the basic components of a firework: Launching Tube Most fireworks are launched from rows of steel tubes or PVD tubes which are secured in troughs of sand or secured to the bases of the trough. The length of the tube is three time as long as the diameter of the shell. The shell should not fit loosely or over tightly into the tube. A loose shell will lose the pressure created from the lifting charge and the shells will not lift out of the tube. Lift Charge When gunpowder burns in the open air, the heat and gas it generates quickly dissipates. But if the gunpowder is confined, say in a pouch at the bottom of a firework cylinder, the heat and gas are trapped and will push wildly at the inside of the launch tube until an explosion results. This explosion will free the heat and gas, and hurtle the firework shell as high as 1000 feet into the air. Time Delay Fuse As the firework shoots through the air, the time-delay fuse continues to burn. When the shell is close to its apex, the fuse has burned low enough to ignite the black powder in the first break (or compartment). Colored stars ignite and are launched in every direction as the fuse ignites the black powder in the second and third break. Timing is critical. In a three-break firework, the middle break needs to ignite at the highest point in the shell's trajectory -- the first break should blow a little before and the third break, a little after. If the timing is off, the firework might detonate too close to the ground. Great care is used in designing the fuses and calculating their lengths. Breaks In a multi-break firework, stars are contained in separate cardboard compartments within the shell. Each container has its own bursting charge which lights and throws out the stars. In order to spread these decorations over a wide area of the sky, the container must burst open with tremendous force. The more the container can resist the explosion and bottle up its force, the bigger the display will be. Resistance comes from the container's heavy wrapping, which is designed to momentarily trap the gas and heat from the bursting charge. PERSONAL EXPERIENCE I chose to explore the world of aerial fireworks primarily because I have experience with them. Most towns around Alaska celebrate the Fourth of July with a large firework display; this is especially true in the Capital. My father is a retired Fire Chief for the Douglas Volunteer Fire Department which allocated me to be part of the fireworks crew for the Annual festivities. The volunteer crew does not get paid to do the work; however the name would suggest that any one could help out, this is not completely accurate because the crew is primarily local fire fighters who have done this work for several years. I?ve helped set up and take down the firework mortar tubes for over 5 years, and, because of insurance reasons, I wasn?t allowed to be on the barge when the „powder? was loaded until I was 18 years old. What barge am I talking about? The fireworks are set up on a large barge and pulled into position downtown in front of the wharf before the show starts. On average, the number of fireworks set off on the Fourth of July in Juneau is about 800 - 1000 fireworks. The show usually last about 15 minutes with the grand finale at the end. The crew usually spends a combined total of over 500 man hours for the complete show. stThe crew first gets together before the 1 of July and wires „squibs? to the fuses on the fireworks. A few days later, the barge is ready to be assembled; this involves unloading the mortar tubes and setting up the layout for the barge. There are usually five rows, two wide, of mortar tubes running the length of the barge. Each tube is then loaded with the correct size of shell and effect. So far, this has been the easiest thing to do. The most complicated and time consuming part of the set up is the wiring. Because of the explosive power of the fireworks, these are not ignited by hand. An electrical charge is sent through the wires which ignites the squibs. The squibs are a longer wire that connects to the fuse, when the charge gets to the end of the squib, there is an ignition of the aerial shells fuse. As an example, the wire used to connect all these fireworks is like a large phone line. If you have ever looked at the inside of a phone wire, there are several smaller lines that are color coded. Each of the colored wires are connected to the squib and then to a control box. The control box is a device that sends a current through each wire when the user completes the circuit. Okay, enough of the technical stuff….I want to give you an idea of how strong these aerial shells are. I had an experience with a 12” shell exploding in the mortar tube. The mortar tube was ?” steel and was about five feet tall; obviously if a 12” shell was in the tube, the diameter of the tube was about 12”. The steel tube was placed in the center of a 55 gallon drum, and sand was compressed between the tube and drum. The shell exploded in the tube, blew the 55 gallon drum in half, and shattered the steel tube. Only once piece of the tube was ever found. That piece of tube is still around for a safety reminder. So, an explosive charge from an aerial shell is enough to break ?” steel. shell hits someone. After the grand finale, the Also, I?ve seen what happens when a 6” tubes that did not launch get a flare dropped down the tube to set the lifting charge off. A person I know ended up getting a 6” shell across the front of his „turnouts? (fire coat) which ended up missing his head, but tearing the front of the coat. Anyone who has ever felt the material on a fire coat can tell you that it would be very difficult to do damage like that to fire coat in a split second. Bibliography Lancaster, Ronald, and Butler, Roy E.A., and Lancaster, J. Mark, and Shimizu, Takeo. Fireworks Principles and Practice. New York: Ticknor, 2002. Pihko, Petri. “Pyrotechnics – The Art of Fire.” 1998. Online posting. Pihko, Petri. 12 April 2003. ~kempmp/pyro.html ProQuest Information and Learning Company. “Physics of Fireworks.” 2003. Online posting. Bigchalk – The Education Network. 12 April 2003. www.bigchalk.com Russell, Michael S. The Chemistry of Fireworks. York, ME: Stenhouse, 2000. “The Physics of Colored Fireworks.” 1998. Online posting. 12 April 2003. ~kempmp/pyro.html