Fireworks: 10 explosive science facts plus bonus slideshow

July 2, 1:05 PMBaltimore Science News ExaminerMary Spiro

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And the rockets 'multicolored' glare. Credit:EpicFireworks

Whenever I get together with friends and family for holidays, I aim to impress (or annoy) them with fascinating scientific facts about the occasion being celebrated. Independence Day should be no different.

A typical pyrotechnics display incorporates elements of chemistry, physics, aerospace engineering, materials science, fire science, psychology, neuroscience, and risk management. The fact that millions of people across America celebrate the political independence of our nation by watching a choreographed multidisciplinary collaboration of basic scientific and engineering principles that result in pleasing visual, auditory, and olfactory stimulation is nothing short of revolutionary (pun intended).

So, in the Spirit of Independent Investigation--a guiding force in our country if ever there was one-- I did a little research, and I have developed a list of 10 “explosive” science facts about fireworks. I tried to select many of these facts come from peer-reviewed journals or other fairly reliable sources. As with any proper research endeavor, however, you’ll have to judge for yourself whether you agree with the scientific findings. I’m no pyrotechnical expert; I just report what I find. I’ve also included a science-laden fireworks slideshow that details the chemical origins of  each spectacular colored burst. So while those around you are “oohing” and awing” as each rocket travels skyward, you can chime in with your own brand of adulation: “Oh, copper” and “Ah, strontium.” You may ignite someone's fuse.

Here goes:

1. A firework is basically a  chemical reaction shoved into a paper tube. They contain the following reactants: an oxidizing agent, a reducing agent, a coloring agent, binders and regulators. Oxidizing agents produce the oxygen that allows the reactants to burn. Common oxidizers include nitrates, chlorates and perchlorates. Reducing agents, such as sulfur or charcoal (a.k.a. carbon) burn the oxygen produced by the oxidizing agent, which in turn, produces the sulfur dioxide or carbon dioxide to propel the firework. Colorants are added. (See slideshow for what chemical makes what color.) Substances like cornmeal are sometimes added as a regulator to slow the reaction process down. Finally, binders such as shellac,  hold all the ingredients together to form a lump called the star. This mixture is forced into a paper tube and cut to size. Now, DO NOT try this at home.
2. Fireworks started out as weapons. Like their military counterparts, they are classified by where they explode, either on the ground or in the air. In the aerial variety,  those that provide their own propulsion are called skyrockets, and those that must be shot into the air by a mortar are called aerial shells. Commonly sold fireworks also include fountains, firecrackers, ground spinners and mines.
3. Fireworks have been known to cause very localized but extremely high contamination with heavy metals. Researchers in Austria examined snow after a New Year’s Eve fireworks display and noted "exorbitant concentrations" of barium, potassium, strontium and iron. However, the contamination did not appear to last and cleared with the next snowfall.  You have to wonder, though, whether the pollutants just didn't migrate to another environment, such as rivers and streams.
4. A Japanese study showed that colored smoke from fireworks was genotoxic (damaging to DNA) to the epithelial cells that line the lungs. In the study, researchers compared the toxicity of various colored smokes to the known toxicity of a control smoke. "All the colored smokes displayed acute toxicity," the report stated. The order of toxicity was orange>violet red>control>yellow. The lesson here: don't breathe the smoke from fireworks, especially the orange ones.
5. Because of the environmental pollution concerns from fireworks listed above,  some chemical entrepreneurs are developing green pyrotechnics. These nitrogen-rich explosives hope to retain the enchanting features of a typical fireworks display without the polluting side effects.
6. Because of fireworks, July may be the most dangerous month. An estimated 85,800 pediatric fireworks-related injuries were treated in U.S. emergency departments during the 14-year study period (1990-2003). Injured children had a mean age of 10.8 years, and 77.9% were male. (No surprise there.)  A 2007 U.S. Consumer Product Safety Commission report stated that fireworks-related injuries sent 9,800 people to the emergency room.
7. In 1992, researchers at Nanyang Technological University in Singapore developed one of the first computer graphics program using a particle system technique to model, render, and animate realistic fireworks displays. The program was able to recreate the appearance of real fireworks in terms of  "color, brightness, shape, trial, size, particle dynamics, blinking, mousing [not sure what this is], star effect, spinning, and elasticity."
8. During the 2008 Olympics in Beijing, a more advanced version of the technique developed in 1992 likely formed the basis for the simulated fireworks shown during the opening ceremonies. Many people were outraged by this phony pyrotechnics show.
9. An article in The New York Times from 1891 reported that “something like $5,000,000” worth of fireworks had been purchased by people in the state and that New York City itself had spent $1.5 million on its annual fireworks display. Let me reiterate,  this was in 1891!  I don't know how much money this represents in 2009 dollars. [Conversion please?] This year however, many cash-poor jurisdictions are reducing or canceling their fireworks displays. Of the ones listed in an article by CBSNews.com, those displays were only costing between $10,000 and $100,000 anyway. [CORRECTION: I re-read the article from 1891, and it says that $5 million were spent nationally and $1.5 in the state of New York. Still, that is is a lot of fireworks. A reader has provided some dollar conversions below.]
10. Planning an exciting and safe fireworks display is all about math. The ratio of shell size to burst diameter is about 1 to 4. For example, a tiny 2-inch rocket shell will produce a burst with a diameter of up to 90 feet. An 8-inch rocket shell will therefore produce a burst with a diameter of 360 feet. In planning their shows, pyrotechnicians also have to account for the vertical and horizontal distance the rocket will travel. Smaller shells launch with a lower initial velocity than larger shells and therefore do not travel as high into the sky or as far away from their launch site.

I hope you can get out and enjoy a bit of science with your fireworks this year. To whet your appetite for the displays to come, check out the fireworks slideshow included here. In it, you will found out how chemicals determine the color of the fireworks you see. The slideshow is also handy for rain-outs.

For more information on the history of fireworks, go to this website from the Chemical Heritage Foundation.

Slide show photos credits: Multi, EpicFireworks; RED, EpicFireworks; Gold, 9044421@N02; Blue, EpicFireworks; Purple, EpicFireworks; Green, FotoRose; White, Southern Gal;  Yellow, Zoologist; Orange, Ultrahi; Silver, EpicFireworks.

Tell us where you like to watch fireworks or share your fondest fireworks memory in the comment box.