Diwali is around the corner and for years we have been welcoming the festival season with extravagant pyrotechnics (pyro=fire+technic=art of). Fireworks have been around since the 7th century in China and are now used all over the world to celebrate events and festivals like the 4th of July (American Independence Day), Guy Fawkes Day (United Kingdom), Spring Festival (China) of course Diwali and Dussehra and New Year all over the world. These controlled explosives are also used in weddings, parades, parties and stage shows.
This popular gimmick has a simple science behind it that is not very well known. All people do is light the wick and run to a distance with their ears closed and a silly grin on their face, but what really happens in the firework that causes the shiny colourful shower of fire?
There are three kinds of fireworks — ones that cause only sound (seiko bomb, wool bomb), ones that cause just light (anaar, chakkarginni) and ones that cause both sound and light (rockets).
All fireworks cause smoke and leave some residue after exploding.
A firework comprises an explosive in a casing with some ‘stars’. These stars are what emit colour during the explosion of fireworks. The outer shell or casing can be spherical or cylindrical and contains black gunpowder (charcoal, sulfur and potassium nitrate).
When the fuse is lit in a rocket, the first pocket of black powder burns and makes the rocket shoot up. A second fuse inside the casing starts burning during the delay and causes the second pocket of black powder to explode, this time causing the actual display. These ‘stars’ are in the second pocket and this is when you see them in action.
There are different chemicals used to give different colours to the fireworks. Red is the most common and easiest to achieve with strontium. Sodium gives a bright yellow colour and green is achieved by barium. For the blue colour, which is most difficult to get, the stars are made up of copper and chlorine compounds while magnesium stars cause white light.
The detonation of different colours is achieved by coating the stars, that actually look like little black marbles, in different chemicals. As the fire burns layer by layer from outside in, different colours erupt causing the much coveted razzle dazzle of a fireworks display. There are some fireworks that have a beautiful shimmering effect, which is achieved by using titanium.
Through trial and innovation, these fireworks exude not only colour but also different shapes. The placement of these stars in the casing determines the shape of the detonation in the sky. The stars can explode in a smily face, star shapes, different lettering, and now even cubes. These patterns are what pyrotechnic experts are working on and thus we have something new in the market every year.
There are some fireworks though, like the sparkler (phool jhari), that does not produce any sound but sparkles on for a minute or so, happily crackling away. This very controlled firework consists of a fuel, like gunpowder, an oxidiser, like potassium nitrate, bound with sugar or starch together with iron or steel powder. This mixture is bound on a wire inside a tube till it sets. Once you set fire to it,
it burns slowly like a cigarette. The proportion of the fuel with the oxidiser determines the speed.
The firecrackers that produce only sounds are basically casings filled with gunpowder. These firecrackers need not produce light and so are not as complex as the multi casing aerial pyrotechnics.
The largest fireworks display in history is the one that celebrated the 50th anniversary of Kuwait's constitution where 77,282 firework projectiles were launched on the night of November 10, 2012. No display has beaten it yet.
Fireworks though beautiful and magical, are a big cause of pollution, especially in India during the months of October-November. The pollution is not just of air but also noise.
It is not just smoke that causes the air pollution. Some of the chemicals used in the stars oxidise to become toxic. These cause a heavy metal dust to settle in the atmosphere causing breathing problems in humans and animals. The residue also settles on water bodies causing aquatic life to suffer.
Yes celebration is good, but we should always be responsible and safe when it comes to these explosives, because even though controlled, these tiny powerhouses can be extremely dangerous.