Construction

The practical aspect to fireworks is just a s important as the theory calculations regarding the temperature and wavelengths at which certain fireworks occur are useless to pyrotechnicians unless the knowledge can be put into practice.

Sights such as the that pictured above originate from small shells. They are reliant on lift charge in order to propel the shell into the air. This process is kick started by use of a time fuse which leads up to the shell causing it to explode.

The energy from this propels the shell containing black powder and star pellets from the launch tube into the air. Attached to this is a Time delay fuse which is the source of the final explosion where the stars are released into the sky.

Click on the interactive image below for more detail on the construction of fireworks.

Lift Charge

The original fuse that is lit from the ground causes the combustion of black powder (Potassium Nitrate, Sulphur and Charcoal) within a confined space hence resulting in a huge explosion due to a massive increase in heat and gas within the shell. The strength of this explosion can hurtle the firework as high as 1000 feet into the air.

Fuse

Fuses are now made of electrical wires connected to a firing panel. Current rushes through this wire creating a spark at the point of contact. This causes lift charge and simultaneously lights a time delay fuse ready to explode the firework when it is airborne.

Launch Tube

The launch tube is quite possibly the most important aspect to the firework. If the firework shell within the launch tube does not tightly fit inside it, gas formed on the combustion of the gunpowder will be able to escape and this results in a loss of pressure hence the explosion essential to aerial lift will not occur.

Black Powder

As discussed in the history of fireworks, the composition of Black Powder remains as:

KNO3 75%

C 15%

S 10%

Stars

This is where the colouring agents come into action. They are placed with black powder into tiny pellets which explode into huge sprawling shapes.

The way in which the stars are packed into the shells dictates the exploding shape they will adopt. Often they are placed into different compartments within the shell, each with its own sub fuse so that different colours will burst at different times.

The different shapes that can arise are illustrated below.

Time Delay Fuse

This is ignited from the initial explosion that occurs when the firework is still stationary on the ground and continues to burn as the shell is propelled into the air.

The fuse burns to the first break, then the second, third …etc depending on how many bursts are required from the firework.

Break

The break is the final part to the firework. It is the position at which the last explosion occurs and dictates the strength of the viewed firework.

The stronger the material of the break, the more it resists to increased pressure until eventually, the pressure overcomes its strength and results in a tremendous explosion.