The Chemistry of Fireworks

A firework is an incendiary device or material that can be used forsignalling orentertainment. There are chemicals located in the nose ofthe rocket that explode, producing the colours seen.

The art of fireworks, first originated in ancient China, with thefirst explosive being made from a mixture of black powder during theSung dynasty. It is believed that the explosive mixture was created bya combination of sulfur, saltpeter and charcoal. The Chinese foundthat the combination of these ingredients was extremely flammable andwould explode if set alight.

Fireworks were originally created for the purpose of entertainment andtoday they are still widely used in celebration to mark specialoccasions. The thrill and excitement generated by fireworks,brightening the night sky and immersing it with vivid displays ofcolour and technicality, which makes them a crowd pleaser.

Behind all the excitement of fireworks, chemistry plays an importantrole in creating the vivid colours we witness lighting up the sky. Theactual chemical reactions that take place in the explosions requirethe use of oxidisers, reducing agents and binders. The additions ofvarying metal chlorides add the colours.

(See Table 1)OxidisersAn oxidizing agent producing the oxygen required to burn the mixtureReducersAn agent e.g. Sulphur, that burn the oxygen and produce hot gasesBindersRequired to hold the mixture in a lumpTABLE 1: Oxidisers, Reducers and BindersThe ability of producing coloured light from the principles offireworks have allowed this technology to be applied for bothindustrial and military uses. Fireworks are now used for flares andsmokescreens in modern society.

In Australia the non-authorised use of fireworks are banned due to thepossibility of death or injury caused by stray rockets anduncontrollable explosions. Care is also needed because fireworks candamage your hearing and the fumes produced are toxic.

Chemical Background:The production of light in fireworks, rely on basic chemicalprinciples such as redox reactions, combustion and the excitement ofelectrons in metal ions when heated.

Redox reactions are chemical reactions in which both oxidation andreduction take place. Oxidation is a process where oxygen is gained,or hydrogen lost and reduction is where oxygen is lost and hydrogen isgained. In order for the reactions to take place in a firework,oxidizers such as nitrates produce the oxygen to burn and reducerssuch as sulphur reduce the oxygen into hot gases. (Scheme 1)NO3 (s) + S (s) ÞNO (g) + SO2 (g)Scheme 1With any explosive device, combustion occurs. Combustion is a processof rapid oxidation of a substance with simultaneous release of heatand sometimes light.

This is important in fireworks because of theredox reactions that occur. During combustion of fireworks someundesirable gases can be produced such as sulphur dioxide, whichcontributes to acid rain and air pollution. (Scheme 2)S (s) + O2 (g) ÞSO2 (g)Scheme 2Fireworks require chemical reactions to create the vivid colours thatare emitted. However there are three essential chemical items neededto allow the reactions to occur. They are an oxidizer, to produceoxygen needed to let the firework burn, reducing agents to burn theoxygen emitted to produce hot gases which glow (Heat causes asubstance to become hot and glow) and binders that hold the mixtureinto a lump.

Oxidisers The common oxidisers are nitrates, chlorates or perchlorates. They arenecessary because they produce the oxygen to burn the mixture.

Nitrates are composed of a metal ion and a nitrate ion and in areaction release one third of their oxygen. (Scheme 3)2NaNO3 (s) Þ2NaNO2 (s) + 3O2 (g)Scheme 3Chlorates are composed of a metal ion and a chlorate ion and releaseall of their oxygen, causing a more speedy reaction. Chlorates are anexample of complete combustion in which all the oxygen is burnt andthe maximum quantity of heat energy is released. This results in avery explosive chemical reaction and caution is required. (Scheme 4)KClO4 (s) ÞKCl (s) + 2O2 (g)Scheme 4Reducing Agents—————Reducing agents work by burning the oxygen that the oxidisers release,producing hot gases. Two common reducing agents are sulphur andcharcoal. The two of these react with oxygen to form sulphur dioxideand carbon dioxide respectively. (Scheme 5)S (s) + O2 (g) ÞSO2 (g)C (s) + O2 (g) ÞCO2 (g)Scheme 5Normally pyrotechnics will combine both of these reducers togetherresulting in a slower reaction.

Therefore reducing agents are used tocontrol the speed of reaction. To speed the reaction, metals are oftenadded, since metal ions are highly reactive because they can generatehigher temperatures and produce brighter light. (Collision Theory -see table 2)Collision Theory(Temperature)”As the temperature of the reaction mixture is increased, the averagekinetic energy of reactant particles increases. More collisions inunit time have energy in excess of the activation energy and thereforethere are more productive collisions in unit time.” (ESSENTIALSTEXTBOOK pg 159)TABLE 2: Collision TheoryThe finer a powder is, the faster a reaction will occur. For examplewheat will burn slowly, whereas wheat powder floating in air willexplode. (See table 3)Collision Theory(Surface area)”As the surface area of a solid reactant increase, more particles ofthe reactant are exposed to collisions with other reactant particles.

This results in more frequent collisions between reactant particles”.

(ESSENTIALS TEXTBOOK pg 160)TABLE 3: Collision TheoryTo slow a reaction down, a thick, compacted substitute such as cornmeal can be used because it is a slow burning organic compound likewheat. By using certain quantities of corn meal and metal ions, it ispossible to regulate the speed of reaction because they burn atdifferent speeds and generate different temperatures.

BindersBinders simply hold the mixture into a nice lump. To bind the lump,either dextrin damped by water or a shellac compounded damped byalcohol are used.

The ColoursThe way that metal ions react when exposed to heat is the principlebehind colour production. Each metal ion produces a specific colour(see TABLE 4). The colour is produced when the electrons in the metalions are “excited”, causing them to “jump” to a different energyshell. It is when the electrons return to “ground state” that theyemit the light as
listed in the table 3.

Colour Compound Name Chemical FormulaColourCompound NameChemical FormulaBlueCopper acetoarsenateC4H6As6Cu4O14 CuCO3, CuS, CuC2O4TurquoiseCopper(1) chlorideCuClYellowCryoliteNa3AlF6 NaHCO3, NaNO3, NaClO4PinkCaCO3, CaSO4, CaC2O4RedLithium carbonateLi2CO3Brilliant redAnhydrous strontium carbonateSr(NO3)2 SrCO3GreenBarium carbonate================BaCO3 Ba(NO3)2, Ba(ClO3)2Bright greenBarium chlorideBaCl2PurpleSr and Cu compounds with calomel (deepens colour)WhiteMg and Al compoundsTABLE 4: Colours of specific metal ionsThe components of a modern firework include, the following: a launchtube, lift charge, fuse, black powder, break, stars and a time delayfuse. TABLE 5 on the following page gives a detailed cross section ofa modern day firework and explains in greater detail the role of thementioned components.

Cross Section of a Firework[IMAGE]Break: In a multi-break firework, stars are contained in separatecardboard containers within the shell. Each container has its ownbursting charge, which lights up and ‘throws’ the stars outward. Inorder to spread out the stars great distances, the container mustburst open with a great amount of force.

Time Delay Fuse: As the firework shoots through the air the fusecontinues to burn. When the shell is close to its apex, the fuseshould have burnt low enough to ignite the black powder.

Stars: Stars are the cargo that is carried by the aerial firework. Itis about the size of your fist and when ignited create the flashes ofcolour and light. The colour emitted depends on the mixture ofperchlorates and metal ions in the star.

Black Powder: The powder is similar to gunpowder and the formula is75% potassium nitrate, 15% charcoal and 10% sulfur.

Launch Tube: Most fireworks are launched from rows of steel tubes thatare secured into troughs of sand The launching tubes tend to be threetimes longer than the height of the firework, but similar in diameter.

The snug fit is to allow the pressure created in the tube to propelthe firework into the air.

[IMAGE]Fuse: Today’s fireworks use electric circuits to activate thelaunching process for obvious safety. With the push of a button, anelectric current rushes through the wire and creates a spark at thepoint of contact. The main fuse lights two secondary fuses. The firstbeing a fast acting side fuse that ignites the lift charge and thesecond being a time delay fuse that ignites the black powder and star.

Lift Charge: When gunpowder burns in the open air, the heat and gasgenerated quickly dissipates. By adding gunpowder to the base of thefirework in a small compartment, it allows the heat and gas trapped tothrust the firework upward allowing a height of up to 300 metres to bereached.

(Images from How Things Work http://www.howthingswork.com)TABLE 5: Cross section of a firework[IMAGE]Social SignificanceThe social significance of fireworks in today’s society is to providea means of nighttime entertainment. In addition, the principles offireworks and pyrotechnics have been applied for uses within industry,search and rescue and for warfare. From its humble beginnings asfirecrackers (SEE FIGURE 1), the development of this technology by theChinese, Europeans and Arabians has seen more spectacular colours andrange of fireworks to be produced (see TABLE 6).

(FIGURE 1: a firecracker)Types of fireworks that existType of FireworkDescriptionFirecrackerUsed primarily for soundRoman CandlesCylindrical containers that emit balls or stars of fires at intervalsPinwheelsFireworks mounted around a wheel. When discharge, causes the wheel tospinPastillesSpirally coiled tubes that rotate when lightedSky RocketRocket propelled object that explodes high in the air to producecoloured displays.

TABLE 6: Types of fireworksA major development during the middle ages saw the explosiveproperties of fireworks used in warfare and ballistics. The Chinesefirst used the firework to create a gunpowder-based weapon againstMongol invaders (see TABLE 7). During the start of the industrialrevolution, the light-emitting concept of the firework was applied forindustrial applications and even in World War II it was used toilluminate the battlefield. See TABLE 7 for more details.

The roles of fireworks throughout human society:History of fireworksThe craft of firework making first existed in Ancient China beforespreading to Europe. The Chinese had been making war rockets andexplosives as early as the 6th century. The art of using these newdeadly weapons spread to Arabia in the 7th century and was given thename “Chinese Arrows”. China claims that they first made gunpowderduring the Sung Dynasty (960-1279AD) and used their war rocketsagainst Mongol invaders in 1279AD. Historians believe that it was theMongols who probably introduced Chinese gunpowder to Europe in about1241AD.

Industrial applicationsThermite that is made form granulated aluminum is used extensively inwelding. Flares that are similar to those used by the military areplaced along highways to alert motorists of construction or bad roadconditions. Aircraft as a visual means of communication also usesflares during emergencies.

Military applicationsModern day military use pyrotechnics as an excellent means ofsignaling during the night. Modified pistols with a large barrel areused to fire coloured ‘star’ shells. When they explode they emitlight, just like fireworks. The flares are used as a means ofsignaling. Red is a universal colour for danger, while othercombinations of green and white flares have various meanings accordingto standard codes. During the night, signal flares are used toilluminate the ground for landing operations of men and equipment.

During both World War’s pyrotechnics were mixed with chemicals such aschlorosulphonic acid, hexachloroethane, or titanium tetrachloride,which reacted with the water vapour in the air to produce an opaquecloud. The thick opaque cloud was a ‘smoke screen’ used to protectmilitary forces from the sight of their enemy.

TABLE 7: Fireworks in SocietyIssues of health and safetyApart from the entertainment value, fireworks due to their chemicalnature are dangerous. Fireworks are explosive devices and should betreated with caution because of their ability to inflict injury anddeath. People through ignorance and misuse have been responsible forthe cause of injury and death from the illegal use of fireworks. TABLE8 below, outlines the major health concerns with the use of fireworks.

Health ConcernThe use of fireworks commonly affects humans and pets. There are manydangers associated with the use of fireworks without training orprecautions. They include the misappropriate usage, the handling offireworks by children and faulty fireworks exploding prematurely.

According to former South Australian Workplace Relations MinisterRobert Lawson, he claims, “Each year around 100 people are treated forfireworks related injuries, dozens of fires are started, property isdamaged and hundreds of people and their pets are distressed,”(Appendix 1). Pets like humans have sensitive hearing, and can becomestressed by the constant loud explosions that are produced byfireworks.

Fireworks also pose a major health risk by individuals not taking careor precautions when either handling or observing fireworks. InAustralia the possession of fireworks for private displays have beenbanned for safety concerns, especially regarding the presence ofillegally imported fireworks from China, which have not passedAustralian safety regulations. The sound produced by fireworks canpeak at up to 160 decibels. Professor Deepak Prasher, an audiologistat University College, London, says the noise generated by fireworksis a neglected health risk. It reaches officially deafening levels andfor people with sensitive hearing the damage can be permanent(Appendix 2).

To manage the problem of injury from firework related cases, theproblem needs to be managed globally through the banning of fireworksto individuals without a license. (See TABLE 9 for SA new laws). Inareas were fireworks are still legal, education is the best way ofinforming people of the dangers of fireworks and it is important toteach individuals safety techniques in handling and usage.

TABLE: 8: Health ConcernsOn November 23, 2001 the South Australian Government established newlegislation to regulate firework use to prevent the possibility ofdeath or injury due to illegal usage. TABLE 9 below lists the newstate laws to protect individuals from fireworks.

1The private sale and use of fireworks is banned.

2All fireworks displays conducted in SA will be limited to licensedpyrotechnicians.

3The possession of fireworks by persons other than licensedpyrotechnicians, permit holders or licensed resellers is an offence.

4Strict safety rules for displays are laid down in the Regulations.

These relate to the minimum distances between the fireworks andspectators, buildings and roads.

5Displays will only be allowed between 4pm and 10.00pm except on NewYears Eve when the permitted hours are between 4pm and 12.30am.

6Pyrotechnicians will have to demonstrate competence before beinglicensed – as there is presently no formal course of instructionoffered at an SA institution, competence must be demonstrated to thesatisfaction of the Director of Workplace Services.

7A notification system will require licensed pyrotechnicians to ensurelocal residents and groups are informed of fireworks displays.

8In remote or regional areas where the attendance of a licensedpyrotechnician is not practicable, community groups will be able toobtain an “exempt permit” to conduct a public display.

9Maximum penalties for breaching regulations in relation to fireworkswill rise from $500 to $5000.

10Police may now issue expiation notices.

11New regulations do not apply to small fireworks such as sparklers, toypistol caps, bon-bons etc.

12String crackers for Asian cultural events will have to meet the newsafety requirements.

TABLE 9: new fireworks regulations South Australia November 23 2001There are other considerations that individuals need to take intoaccount when viewing legal public displays. TABLE 10 below, highlightsimportant considerations that the general public should take intoaccount when next viewing a firework show.

Other Considerations* Spectators should obey all ushers or monitors and respect thesafety barriers* Although it rarely happens, it is possible that a fireworkcomponent might fall to the ground without exploding. The publicshould be cautioned not to touch these fireworks* Pets have very sensitive ears and the booms and bangs associatedwith fireworks can be distressing.

* Leave the lighting of all fireworks to the trained operator whenyou attend a public display.

* Sparklers, fountains and other items that many states allow foruse by private individuals are not appropriate to use when a largecrowd is present* Protect your hearing because fireworks can peak at 140-160decibels.

* Like playing with matches, children should not have access to anytype of firework* The fumes produced from the explosives are toxic, therefore careshould be taken not to inhale the fumes or prolong contactTABLE 10: Health ConsiderationsConclusionThe art of fireworks has evolved greatly since its initial discoveryin Ancient China. From simply a flash of light, the addition of metalcompounds has allowed new and vivid colours to be created.

The basic concept of the firework has been adopted for militarypurposes, initially as war rockets and eventually to its use asgunpowder. In non-threatening ways, the properties of fireworks havebeen transformed into a use for signaling and illumination duringperiods of darkness for both safety and military purposes.

The chemical processes of redox reactions and combustion are presenting the explosion of fireworks. The addition of metal ions are whatcreates the colours as their electrons return to ‘ground state’ afterbeing excited by the heat energy released during the explosion.

In order to make fireworks safe for everyone to enjoy, we must firsteducate each other on how to appropriately view fireworks. It is nowby law, illegal to be in possession of any firework without a permit,which is a positive move toward making fireworks a safe form ofnighttime entertainment.

Fireworks have evolved greatly through the Middle Ages thanks to theEuropeans. The only negative aspect with fireworks is Europe’s use ofthe technology to create gunpowder-based weaponry.

While fireworks are truly fascinating to watch, they are verydangerous because of their explosive nature and the high level ofnoise emitted. Despite all the dangers associated with fireworks, theyshould remain in use within our society for their primary purpose ofentertainment.

Bibliography

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