Sparkle Sparkle boom boom – Firecrackers

by Kavitha — October 12, 2021

What is common between Diwali, 4^th of July, and the Chinese New Year? No prizes for guessing…Yes, it’s the fireworks…The fascinating display of firecrackers, that light up the sky and are the hallmark of these festivities.

Ever wondered about how these firecrackers work? Let’s explore this together.

Firecrackers are technically called Pyrotechnic devices (Pyro means fire). Who would deny that this is not a piece of fire art much like the artist wielding rods of fire whom you see in circuses? Basically, fireworks are of 3 types, the ones that sparkle brightly (sparklers), the ones that explode (firecrackers) and the ones that rise up to the sky and then explode with a beautiful display (aerial fireworks). Each of these though has common features have tiny variations in their design and components that make them function different.

The basic components of the firecrackers generally are the fuel and the oxidizer. Gun powder or black powder is the most commonly used fuel which has charcoal, Sulphur, and Potassium nitrate. Charcoal, the carbon source along with sulphur acts as the fuel while the potassium nitrate acts as the oxidizer. These are tightly wrapped inside a paper cylinder or tube which can be ignited by a fuse that is made of paper or fabric. There are some variants that can be electrically ignited using circuits, and hence can be operated from a safe distance. The fuse when lit provides heat energy which initiates a chemical reaction in the gun powder and the various chemicals in them react to form other types of chemicals some of which are gases like Nitrogen and Carbon dioxide. I’m not going to put this down as an equation but I want you to picture this as it happens inside a small tube of the firecracker. The confined space of the tube is not sufficient to accommodate the expanding gases formed in the reaction thereby generating a huge pressure inside the tube which causes it to explode with a BANG! Voila…now you know how firecrackers work…..

How about the shimmering colorful lights then? So, just as one may add flavors like chocolate, vanilla to your morning milkshake, one could add various other chemicals to this mix to produce colors, shapes, etc. in fireworks. Mostly they are metal salts that light up till they are incandescent and then shine brightly as they burn. These metal flakes can be varied to produce different colors as well. For example, Barium metal flakes produce a green color, Calcium – orange, Copper – blue, Magnesium – bright white, Sodium – gold, and so on.

Sparklers, have in addition to gunpowder, something called a binder which is commonly sugar or starch. These when mixed with water form a slurry which is then coated onto metal wires and dried slowly. The proportion of fuel and oxidizer are balanced very well so as to produce a reaction where the fuel burns slowly instead of bursting like other firecrackers.

Aerial fireworks are a combination of the above two principles – it needs an explosive reaction to propel the rest of the firework to a higher altitude where another explosion creates the stunning display. These firecrackers also called ‘rockets’ have a ‘shell’ which in turn has the following parts:

A stick at the base (to prevent it from exploding on the ground but to gently ensure that it is guided on a trajectory or path up into the sky)
A fuse to ignite the firecracker with a time delay to ensure it explodes in the sky
A charge or motor to initiate the explosion
The effect or the part of the cracker that explodes in the sky and is aerodynamically designed to ensure an aesthetically beautiful trajectory.

A small cylinder below the shell has the lifting charge which exploded when the fuse is lit and in turn lights the fuse of the shell which burns slowly as the unit ascends into the sky and ignites the bursting charge causing it to explode in the sky. The metal flakes and iron filings are arranged very carefully in the shell which in turn amplifies the pattern in the sky which provides the visual treat in the sky. Some of these aerial firecrackers explode in stages causing serial display of these lights and the principle is to have a time delay fuse which ensures that they are serially lit up one after the other in proper order.