Red Fireworks Go Green

Makers of fireworks and flares have long believed that the beautiful red color in their explosions could be attained only with chlorine-based compounds. But after these ingredients combust, they can transform into cancer-causing chemicals that then fall to the Earth.

Now, new chlorine-free pyrotechnics could pave the way for a generation of red flares and fireworks that are better for the environment and for people’s health, says Jesse J. Sabatini at the U.S. Army Research Laboratory, in Maryland. Sabatini developed the red pyrotechnics with Ernst-Christian Koch at consulting firm Lutradyn, in Kaiserslautern, Germany (Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201505829).

Currently, red fireworks get their hue primarily from strontium monochloride, which is produced by burning strontium compounds with polyvinyl chloride and a variety of other pyrotechnic ingredients. Unfortunately, the combustion of these mixtures produces a variety of polychlorinated aromatic chemicals, including some potent carcinogens.

To make the more environmentally friendly fireworks, the researchers focused on strontium monohydroxide, a compound that scientists had long believed was only a minor contributor to the red color of pyrotechnics. According to Koch, for years, scientists hadn’t realized that strontium monohydroxide also strongly flared red because its sister product, strontium oxide, produces an orange-red color that fireworks-makers try to avoid.

Sabatini, Koch, and coworkers formulated the new explosive by replacing polyvinyl chloride on the old ingredient list with either hexamine, a preservative in citrus washing solutions, or 5-amino-1H-tetrazole, an airbag propellant. The replacement successfully removes chlorine and helps produce strontium monohydroxide when the overall concoction is ignited, producing bright red fireworks. As an added bonus, the new formulation also avoids the production of unwanted orangey strontium oxide, Koch says.

“It’s very challenging to go from something that works on the bench to something that works on a large-scale,” comments David E. Chavez, a chemist at Los Alamos National Laboratory who was not involved in the research. But this new combustible formulation might translate to large-scale fireworks displays readily, he says. Because hexamine and 5-amino-1H-tetrazole are widely used in the chemical industry, the new formulation could easily be adopted by pyrotechnic producers.

The potential benefit is not just to those putting on Fourth of July and New Year’s Eve fireworks displays, Chavez adds. The military is also a large consumer of red flares, particularly for training purposes. “Training areas get fallout [from flares] over and over again,” he says. So much so, “that it can be an issue for environmental clean-up,” Chavez adds.

Next up, researchers may want to focus on blue and green fireworks, many of which also employ chlorine in their formulations. One can hope that this work will encourage others to formulate more environmentally friendly fireworks of other colors with similar strategies, says Nigel Davies, a retired pyrotechnics instructor at the Defence Academy of the United Kingdom.