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Many of you will celebrate the New Year by attending a firework display. So in this post I’d like to take you behind the scenes of fireworks. These beautiful explosions of colour and light keep astonishing us and are always accompanied by “oooh’s” and “aah’s” from the audience that is admiring them.
The chemistry of fireworks
A story of how green fireworks could use some “greening”.
By David Dupont
The earliest documentation of fireworks dates back to 7th century China, where they were invented. Today’s fireworks still operate on the same basic principle of igniting a mixture of gunpowder and colouring agents. The gunpowder is a mixture of an oxidising agent like potassium nitrate or perchlorate and a reducing agent like sulphur or charcoal. When this mixture is ignited it produces a large amount of heat that causes the colouring agents to emit light of a certain colour.
Typically consisting of metal salts, colouring agents emit a particular colour depending on the metal.1
It’s all chemistry!
Firework manufacturers carefully tune parameters like grain size, powder composition and packing to produce the most spectacular effects and sounds. In the “multi-break” shells used for fireworks, the chambers contain mixtures of fuels and oxidisers plus compounds for special effects “stars” connected by time-delay fuses so that the chambers explode in stages.
These modern techniques – like time delay fuses, multi-break fireworks and sophisticated launch tubes – have led to ever more spectacular shows.1
The technology behind the BOOM
Recently, attention has also gone to the environmental impact of fireworks.
Perchlorates and some metals like barium are known to have negative side effects and pose serious human health hazards. These compounds are water-soluble and end up in our water and soil after the show, so it is important to consider these issues – even though many will choose to ignore this fact.
In fact, the research on more sustainable fireworks has been going on for a while. Not so long ago mercury and lead- based compounds were still used as colouring agents. They were however phased out and replaced by less toxic alternatives.
Ironically, the modern pyrotechnic compounds that could use some “greening” are the barium compounds that give fireworks their green colour.
High concentrations of metals and perchlorates were found in the vicinity of firework shows, and the only question is how much of these were ingested by the public at the time of the show or afterwards. This issue has led to the rapid development of alternative compounds that could make fireworks more sustainable and environmentally- friendly while maintaining their spectacular and beautiful bangs that light up our festive events.2
Pyrotechnics made from high-nitrogen compounds like nitrocellulose or nitrogen-based heteroaromats and their metal complexes, produce less smoke and particulate matter, and much smaller amounts of perchlorates are required.2,3 Less smoke also means less colour has to be added to achieve the same result.
These modern high-nitrogen based pyrotechnics can reduce the use of metals by up to 90% and even phase out the use of perchlorates.2
Furthermore, their increased stability reduces the hazards associated with uncontrolled explosions of fireworks causing many accidental casualties every year.
At this moment these new pyrotechnics are still more expensive than traditional fireworks, but the pressure for safety and environmental protection is likely to push further developments in this field.3 Less toxic pyrotechnics could open up the way for safer and better indoor pyrotechnics at concerts or theme parks and are also translatable to military and aeronautic applications. In any case, don’t let this story spoil your love of fireworks: they are still a testament to man’s imagination and will, thanks to innovation, remain so for decades to come!
I wish you all a happy new year and lots of dazzling firework shows in the future.
1. Averill, B.; General Chemistry: principles, patterns and applications V1, chapter 6.3.
3. Steinhauser et al.; “Green” Pyrotechnics: A Chemists’ Challenge, Angewandte Chemie, 2008.