Film

Aerial Fireworks

September 7, 2018
A History of Fireworks

The history of fireworks begins with the history of gunpowder in 9th century China.  Gunpowder was probably invented by accident (the compound is a mixture of only three components) but was soon used at both wars and festivals.  Within about a hundred years of the invention of gunpowder, some form of early fireworks were being sold by Chinese street vendors.

Gunpowder spread to Europe in the 14th century in the form of cannons and other military weapons, and with the gunpowder came fireworks.  In the 1800s, fireworks manufacturers began tinkering with the fireworks compositions and soon colored fireworks (and other effects) were lighting up the sky.

Anatomy of an Aerial Shell

Aerial fireworks shells are either a sphere or a cylinder, with spheres being more common.  Common sizes range from three inches (slightly bigger than a tennis ball) up to ten inches (about the size of a basketball).  Shells larger than ten inches are extremely expensive to transport, although they can be legally bought and shot.

A spherical aerial shell is composed of five general parts: the casing, the stars, the flash powder, the time fuse, and the lift charge.  As sparks from machines are deadly in fireworks manufacturing, every firework is made by hand.

The casing is two halves of a ball (for spherical shells), made from layers of paper.  Each half is filled with stars and then the halves are (carefully!) pressed together and taped.  To reinforce the weak seam created by the separate halves, the casing is finished with several layers of glue and paper strips.

Stars are the exciting part of the shell: these are what provide color and most of the effects one observes.  Stars can be manufactured in several different ways; rolled stars are most common in commercial fireworks.  Rolled stars are round and range from the size of a pea to the size of a small grape.  Rolled stars allow for color-changing effects: as one layer is burned away, another layer of a different pyrotechnic composition (ie color) is revealed.  The colors are made by burning metals: titanium and aluminum burn white, barium burns green, copper burns blue, etc.  Those experimenting with new pyrotechnic compositions for stars must be careful about which chemicals are mixed together, as some chemicals react poorly with each other and will result in self-ignition.

Flash powder is placed between the two halves of the star-filled casing and is responsible for fireworks going “Boom!”.  Once the flash powder is lit, the reinforced shell casing will initially resist the force of the expanding gases: this allows time for the stars to light.  The internal pressure will eventually overcome the paper casing and the firework will explode with the sound of a cannon to display its burning stars.  ‘Salute’ shells, with a larger-than-average ‘report’ contain more flash powder than ordinary shells.

Time fuse is what lights the flash powder and what determines when the firework should explode after it has been launched.  Holes are pre-drilled in one half of the casing, allowing for one or more fuse(s) to be inserted into the firework.  Time fuse is similar to 3/8” rope, but is manufactured to burn at specific rates: 3sec/inch, 7sec/inch, etc.  The number of seconds needed for the shell to reach peak height is calculated (a shell should explode at the apex of its trajectory), and the needed length of fuse is cut and inserted into the shell.

Finally comes the lift charge and fuse to light the shell (often quick match).  The lift charge is simple: several ounces of gunpowder to get the shell in the air and light the time fuse.  On commercial shells this may be contained in a cone, or in a small cup similar to a Dixie cup.  Quick match is another fuse covered in paper: almost as soon as it ignites, the paper carries the fire and lights the lift charge.

 

The operator will then load the firework in an appropriately-sized tube (mortar), lift charge down, and either leave the fuse dangling out of the mortar (for hand-fired shows), or attach an electronic match (for electrically-fired shows).

 

Problems with Shells

Unfortunately, we live in an imperfect world.  And in that imperfect world, shells don’t always go off as planned (or at all).

First is flower pots.  Flower pots never make it out of the mortar, instead throwing their bouquet of stars from inside their tube with a tremendous “Bang!”.

Next is hangfires- arguably the worse of the potential problems.  A hangfire is a shell which has been lit, but has not yet left the mortar for whatever reason.  These are Schrödinger’s bombs: while still in the mortar they are simultaneously misfires and duds and may continue to be so for thirty minutes to an hour.

Misfires can be bad.  Like, this-is-the-reason-you-never-put-any-part-of-your-body-over-a-loaded-mortar bad.  Misfires go randomly: either early (ignited by falling embers) or late (a smoldering misfire decided to light).  If you’ve ever seen one random shell go off several minutes after the show, a hangfire turned into a misfire.

Duds are, as their name suggests, inert.  The firework may have gotten wet, it may not have been lit, the time fuse didn’t catch… generally something went wrong and the firework didn’t go off.  A dud may be found either in its mortar, or in the fallout zone around the fireworks area (this is the main reason why fireworks crews bar entry to what otherwise seems like the perfect place to watch fireworks: a grapefruit hurtling towards earth at terminal velocity).  Duds are rendered completely inert with water, and then transported back to the fireworks supplier for proper disposal.

 

Regulating Bodies

Fireworks are explosives and so are potentially subjected to federal, state, county, and city regulations.  On the federal level, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) covers firework requirements when the fireworks are not in transit and the Department of Transportation (DoT) rules when fireworks are in transit. 

On the state level, most states have adopted various versions of the National Fire Protection Agency’s (NFPA) 1123 or 1126 standard (depending on the type of firework).  Fireworks operator’s are licensed on the state level and applicants generally have to provide evidence of working on shows as well as passing a written test based on state law.

The local level is where the Authority Having Jurisdiction (AHJ) usually resides, as well as local laws about prohibited fireworks.

Further Reading

Wikipedia’s “Fireworks”

Wikipedia’s “Gunpowder”

ATF’s “Fireworks”

DoT’s “Fireworks”

America Pyrotechnics Association’s “State Law Directory” for Consumer Fireworks

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