How Fireworks Work: An Overview Of The Chemistry And Physics

Fireworks have fascinated people for centuries, lighting up the skies with vibrant colours and loud explosions. However, behind these captivating spectacles lies a complex interplay of chemistry and physics. Understanding how fireworks work step by step, including the temperatures they reach and the forces at play, reveals their scientific marvel. This article also explains how to handle them safely to ensure their magic remains unharmed by accidents.

THE ANATOMY OF FIREWORKS

At the core of every firework is a carefully designed system of components working in harmony. Each part has a specific role in delivering light, colour, and sound explosion.

The shell or casing is the firework’s outer layer, often made of cardboard or paper, which houses the inner components. Inside the shell lies the lift charge, typically a mixture of black powder containing potassium nitrate, charcoal, and sulphur. This is the propellant that launches the fireworks into the air. A fuse system is attached to the lift charge, designed to ignite the firework at the correct altitude between 30 and 300 meters (100 to 1000 feet). The fuse system is a time-delayed ignition system that ensures it does not activate.

The centrepiece of a firework is the bursting charge, another black powder mixture located within the shell. Surrounding the bursting charge are stars—small pellets containing the ingredients responsible for producing the colours and effects. These stars are made of a combination of oxidisers, fuels, metal salts, and binders.

THE CHEMISTRY

Fireworks owe their vibrant colours and effects to chemistry. The stars contain specific chemical compounds that determine the display’s colours. For instance:

• Strontium salts produce red hues.

• Barium compounds create green.

• Copper salts give off blue light.

• Sodium compounds generate yellow.

• Calcium salts add orange tones.

• Magnesium, aluminium, or titanium provide intense white sparks.

The intense heat excites the metal atoms in the stars when the firework explodes. Electrons in these atoms absorb energy and jump to higher energy levels. As they return to their ground state, they release energy as light, with the colour depending on the specific energy gap between the states.

THE PROCESS

1. Ignition and Launch: When the firework is lit, the lift charge ignites, rapidly combusting to generate hot gases. This explosion propels the firework skyward, often reaching speeds of 240 kilometres per hour (150 miles per hour).

2. Reaching Peak Altitude: As the firework climbs, the time-delayed fuse burns. By the time the firework reaches its peak altitude, the fuse ignites the bursting charge.

3. The Main Explosion: The bursting charge generates temperatures of over 1300°C (2400°F), causing the casing to rupture violently. This explosion scatters the stars and other payloads.

4. Color and Light: The intense heat excites electrons in the metal atoms within the stars. As these electrons return to their ground state, they release energy in the form of light. The colour of the light depends on the chemical composition:

   • Copper compounds produce blue light.

   • Strontium compounds yield red.

   • Sodium salts give yellow.

   • Barium compounds create green.

   • Magnesium or aluminum produces bright white sparks.

5. Patterns and Effects:The arrangement of stars inside the firework shell determines the shape of the explosion. For example, a circular arrangement produces a spherical burst, while specific patterns create shapes like hearts or stars.

6. Sound Production:The loud booms and crackles come from the rapid expansion of gases and the bursting of the firework shell. Additional effects, like whistling or crackling, are achieved by using specific additives like titanium or zinc.

   
   

THE PHYSICS

Fireworks operate on Newton’s Third Law of Motion: for every action, there is an equal and opposite reaction. The lift charge generates force downward, propelling the firework upward. The force of the explosion disperses the stars radially, with the velocities and trajectories dictated by the firework’s design.

The sound waves created by the explosion travel at the speed of sound, roughly 343 meters per second (1125 feet per second) at sea level.

THE NUMBERS: TEMPERATURE & DISTANCE

• Lift charge combustion: Up to 870°C (1600°F).

• Bursting charge explosion: Over 1300°C (2400°F).

• Launch height: Between 30 and 300 meters (100 to 1000 feet).

• Velocity: Approximately 240 kilometers per hour (150 miles per hour).

HOW TO USE FIREWORKS SAFELY

Despite their beauty, fireworks are explosives that can reach high temperatures and travel significant distances, posing risks if not handled responsibly. Here are guidelines to ensure safety:

Before Using Fireworks

1. Understand Local Laws: Fireworks regulations vary, and some areas restrict or prohibit their use. Always comply with local laws.

2. Choose a Safe Location: Select a large, open space free of trees, buildings, and flammable materials. Ensure the ground is stable and flat.

3. Prepare Safety Equipment: Have water buckets, hoses, or fire extinguishers ready.

   
   

During Operation

1. Ignite Safely: Use a long-handled lighter or punk (smouldering stick) to ignite fireworks from a safe distance.

2. Never Relight Duds: If a firework fails to ignite, wait at least 20 minutes, then soak it in water before disposal.

3. Keep a Safe Distance: Spectators should stay at least 30 meters (100 feet) away from fireworks.

   
   

After the Display

1. Cool and Dispose Properly: Soak spent fireworks in water before discarding them in a metal container.

2. Inspect the Area: Check for stalled fireworks or embers to prevent accidental fires.

Always celebrate responsibly and let the sparks fly!