Image by John Harke
Technical

Fireworks – An Explosive Industry

A cold, pitch black evening in the English countryside with the ground frozen solid beneath your feet. You look around to find yourself in the middle of a hundred pounds of explosives, blowtorch in hand, ready to provide entertainment to an eagerly waiting crowd. The crowd begins the countdown, your heart rate increases slightly, then with a brief lick of a flame to a gunpowder fuse, fizzle fizzle fizzle, thump! Explosives being launched hundreds of feet into the air with “oohs” and “aahs” from an amazed audience.

The fireworks industry has come a long way from when the Chinese originally concocted gunpowder in the 9th century. The principles, however, are fundamentally the same. 

You might remember the fire triangle from school days. To sustain a fire, you must have fuel, oxygen, and heat. In fireworks you have charcoal as a primary fuel, an oxidizing agent such as potassium nitrate to provide the oxygen, and a burning fuse to supply the initial heat. Using a variety of metal salts can change the color of the reaction to create a dazzling array of colors seen in the sky.

Examples of different salts used to create different colors (source)

Most fireworks are two stage devices. The first stage fires the effect into the sky and the second one explodes at apogee (the highest point in the sky) distributing the effects.

A cross-section of a professional firework shell (source).

Fireworks shells burst from tubes knows as mortars. A bag of gunpowder ignites below the firework that produces a huge volume of burning gasses – launching the firework into the sky at speeds that can exceed 300mph. (Using some simple rocket science, the force required to accelerate a couple-hundred-gram mass from 0-300mph in two or three feet is immense!) 

This simultaneously ignites a time delay fuse which will burn for a predictable time. A few seconds after launch the fuse will reach the center of the shell and ignite a burst powder. This provides enough force to break open the shell casing, igniting all the effects (called stars) and distributing them in the sky. 

The majority of firework effects rely on the above principle, just in various sizes and shapes. They can be shrunk down, put into multiple small cardboard tubes and fused together creating a cake – a traditional consumer firework.

100-shot fan cake used in professional displays with electronic ignition (source).

The legality of fireworks varies massively around the world. In California, consumers are not allowed to purchase fire cakes or shells, but in other states, consumers are allowed to buy them freely. In the UK (where I used to live) you can buy cakes but not shells as consumers. The only way you can get around these restrictions is to bring in a professional fireworks company to fire your display. 

Professional companies have access to much larger, more powerful and dangerous items. Different countries, again, have different regulations on what you have to do to become a professional and gain the ability to use such items by a licensed company. 

Running around in dark fields with blowtorches may sound a touch rudimental in today’s high-tech world. You probably won’t be surprised to hear computer systems can be used to make shows more impressive and safer. 

Pyromusicals provide the most impressive and captivating experience for any audience by blending carefully chosen music with precisely choreographed fireworks. There are many systems on the market that provide this functionality, but the FireOne system is one of the leading.

It allows thousands of individual items to be fired (called cues) with 10millisecond accuracy. It uses a patented capacitor discharge system to ignite effects through devices known as e-matches. These small devices contain a tiny amount of temperature sensitive compound coating a small nichrome wire. When a current passes through the wire, it heats up igniting the compound, creating a shower of sparks and hot gasses. This is enough to ignite any firework effect reliably. The devices also ignite almost instantaneously giving precise control of firing time and can be inserted straight into the firework device, eliminating any fuse delays. 

A typical FireOne system control panel (source).

An ematch that provides a small explosion when a current is passed (source).

Mixing explosives and electronics can be a little hazardous if not done carefully. The electronic devices used to fire the displays have to be incredibly robust to survive extremes of temperatures, heavy rain, and proximity to detonating fireworks. 

From an electrical engineering perspective, these devices have a lot of built-in redundancy and mechanical features to try and best protect the sensitive innards. When performed correctly, it can provide some of the most impressive shows, such as this one that I was fortunate enough to work on four years ago. (A large pyromusical display in Billericay, Essex, UK)

When things go wrong with electrical systems, it can be rather spectacular. One of the most famous examples is the San Diego July 4th show in 2012. 

An error by a fireworks technician led to an ‘all-fire’ alert. The firing system obliged, launching the entire show in an instant. The result may have been impressive, but certainly not what was intended. These events remind us of the immense power of the devices we are handling. 

This would have looked a lot more impressive if spread out a bit!

Fireworks demand respect from operators and proper training is essential. Keeping safe distances, wearing appropriate safety clothing and preparing emergency procedures in advance is paramount. 

By merging the worlds of electrical engineering, chemistry, and art you can create unforgettable experiences using the sky as a canvas. There is something very addictive about blowing things up in a colorful and controlled way. 

The next time you’re looking out the window at distant fireworks, take a moment to think about all the engineering, planning and expertise that goes into bringing excitement and wonder to audiences young and old.