Acknowledgements
President: Christine Scicluna
Social Policy Officer & Policy Paper Leader: Cristina Stafrace
S-Cubed Administrative Board: Anthea Spiteri, Giulia Montebello, Louisa Degabriele & Elisa Caruana
S-Cubed Executive Board: Dorian Abela, Daniele Caruana, Claire Pace, Luke Said, Clarissa Attard & Julian Spiteri
Social Policy Subcommittee: Dindora Mercieca, Martina Debono, Claire Pace, Juergen Valletta & Matthew Clark
Special Mentions: Servolo Delicata, Johnny Vella & Lourdes Fireworks Factory (Qrendi).
Introduction
From events to national holidays to religious celebrations, fireworks are a part of countless celebrations around the world and have come to represent joy and happiness globally. However, behind the dazzling array of colours, shapes and patterns they are supported by millennia of engineering and continuous improvement in science. It can be stated that fireworks are composed of three main components: coloured light, noise and smoke, which once ordered have the potential to give the spectacle which is loved by many.1,2
From their beginning in 7th century BC China till now, fireworks have evolved significantly.2 Gunpowder made its way into Europe in the early 1200s, and is considered as the precursor of modern fireworks. Although they were limited in sparkles, orange hues were still present due to the glow of very hot solid particles, caused by a phenomenon called, black-body radiation. Moreover, on further development of newly synthesised compounds, multi-coloured explosions started to be seen, with the colours being displayed as a result of spectral emissions of excited gas-phase molecules instead of from black-body radiation 3 Whether it is strontium carbonate for red fireworks, or barium chloride for green, it is evident that the burning of specific metal salts, originally packed into small pellets referred to as ‘pyrotechnic stars’, would produce this intense colour 4
The earliest fireworks display was mainly composed of hand-lit fireworks which exploded at ground level. However, with major technological and scientific advantages, these displays have become much more complex and are executed with utmost precision even by computers which are able to coordinate launches with a score. Moreover, such advancements and the acquisition of finer materials for launch sites and mortars, also made this craft relatively safer for operators, allowing them to view launches from a safer distance away Additionally, further research on salts and the chemistry behind it all, has given the opportunity to explore more colourful combinations and patterns.2
Therefore, the making of fireworks can be considered a fairly complex process which requires precision and a well-maintained controlled environment as from one misalignment to too much black powder, things can go wrong
quite easily.4 However, with fireworks being imbedded in our cultures for thousands of years, it is of no doubt that their scientific and environmental progress will continue to evolve.
The Production Process
The production of the different components of a firework includes a variety of raw materials. The outer part of a firework known as the shell holds the ammunition inside and is made up of plastic, papier-mache or heavy paper. Most of the fireworks are made up of cylindrical pellets known as stars Stars have three main components; a fuel that burns providing heat which allows the firework to ignite, a colouring agent and an oxidiser that burns the fuel. Fuels may be either slow burning such as charcoal or dextrin that demonstrate a dim but long-lasting display or fast burning like aluminium that produces an extremely bright but short-lasting effect A combustion reaction occurs upon the interaction of the fuel with the oxidiser, due to a transfer of electrons allowing energy to be released.5,6,7
The preliminary step in the synthesis of stars includes weighing and the sifting of different powdered chemicals together through brass screens to avoid the generation of sparks. The powder is then either mixed by hand or inside a rotating drum. If the latter procedure is used it must be ensured that the generation of heat as a product of friction is avoided The transfer of the powders from the mixing room to the cutting room is carried out in wooden barrels. Water is added to the powdered chemicals, transforming it into a soft dough which is moulded using a wooden mallet when still wet. The moulds are covered in black powder; a mixture of potassium nitrate, charcoal and sulphur in a 75:15:10 weight ratio and left to dry 5,6,7
The stars are arranged inside a cylindrical container, and the way in which the pellets are arranged within the shell determine the shape of the firework. A paper cap is placed on the filled container, known as a break which undergoes a spiking process by tying a string to the break and winding it around until it is completely covered. The spiking process can be omitted for some breaks and instead heavier cardboard is used. A fuse is inserted into the break and heavy paper is wrapped around it Once wrapped the breaks are
moved to the pasting room and rewrapped in heavy, paste-soaked paper and allowed to dry, hardening and forming a tight seal 5,6,7
The shell is assembled by stacking the components tighter. At the bottom of the shell, a small circular compartment is present which holds the black powder propellant An alternative to black powder is flash powder which is used in commercial fireworks and is characterised by a bright light and a loud noise. A starting fuse is attached, after which the firework is wrapped in heavy paper, and the package is tied with string.5,6,7
The Physico-Chemistry of Fireworks
One way of better understanding how fireworks work is by studying them from a chemical perspective. As shall be seen, physico-chemistry and chemical reactions help us answer questions about the inner workings of pyrotechnics. How are fireworks launched? What creates the explosion? What generates colour in fireworks?
Generally, fireworks are launched up to an altitude of a couple hundred metres. Therefore, they must gain a lot of gravitational potential energy to rise upwards against the force of gravity This energy is initially stored as chemical potential energy in the fuel, and a combustion reaction takes place so that this energy is transformed into gravitational potential energy
Black powder is the major propellant fuel in pyrotechnics and comprises of a mixture of three components: potassium nitrate (KNO3), charcoal (C), and sulfur (S) This chemical mixture is first applied with an ignition or spark that increases the temperature of the system and starts breaking down the bonds within each of the chemicals. As a result, the three components react through an oxidation-reduction reaction. This is explained by equations 1 to 3 which represent the simultaneous processes taking place, i.e. the reduction of nitrate to nitrogen gas, the oxidation of sulfur to sulfate, and the oxidation of carbon to carbon dioxide gas and carbonate, respectively. These half-reactions are combined in equation 4 to give the overall redox equation.8,9,10,11
As we can see, a lot of gas is generated by the combustion reaction This gas escapes through the bottom of the shell, and as it leaves with an inherent force, it creates an equal and opposite force, by Newton’s Third Law of Motion, on the firework, thus lifting it upwards. The energy in the system has therefore been converted from chemical energy to kinetic energy, and eventually to gravitational potential energy as the firework rises upwards.8,9,12
Black powder is also used as a fuel in mechanical ground fireworks. In these pyrotechnics, such as the commonly known Catherine wheel, the burning of the black powder generates both a flame, as well as gaseous products that propel and drive the system into motion.13
Apart from potassium nitrate, there are other oxidisers which are used to burn fireworks. One example which is used extensively in the local scene is potassium perchlorate (KClO4). At high temperatures, following the ignition of the firework, the perchlorate decomposes to produce oxygen as observed in equation 5 This supply of O2 oxidises the rest of the mixture and aids it to continue burning and to combust, thus generating the explosion of the firework 9,12
KClO4 KCl + 2O2 Equation 5 →
The perchlorate salt was introduced in pyrotechnics as an alternative to the very reactive potassium chlorate (KClO3) The latter was banned after having caused several fatal accidents Factors such as exposure to sunlight, slight increases in temperature, and exposure to friction or impact all aid the combustion or explosion of this substance. Equation 6 illustrates the violent reaction of potassium chlorate with sulfur dioxide. This reaction in turn produces the highly explosive chemical chlorine dioxide.12
SO2 + 2KClO3 2ClO2 + K2SO4 …..Equation 6 →
A variety of metals are also included in the firework mixture to serve as fuel. Such metals include aluminium, magnesium, and titanium, and these act as reducing agents to reduce the oxidisers mentioned previously.9,12
Furthermore, additional chemicals, referred to as stabilisers, are added to the pyrotechnic mixture to prevent the violent reactions and premature decompositions of fuels and oxidisers. The weakly acidic boric acid (H3BO3) is one such stabiliser which prevents the decomposition of aluminium. By acting as a buffer, H3BO3 stabilises the pH and does not allow any nitrates present to oxidise the aluminium.14
Moreover, some very interesting spectrochemistry and quantum theory comes into play to generate different colours in fireworks. Chemical substances are fundamentally made up of atoms, each of which is surrounded by electrons separated into different subshells. Electrons in different shells possess different amounts of energy, with the outermost electrons around these atoms having the most energy and being capable of causing reactions. When these atoms are exposed to energy generated during the combustion reaction of fireworks, the outermost electrons absorb this energy and are excited from their ground state (normal energy level). As a result, they move further outwards, away from the nucleus of the atom.15
However, these electrons do not remain in this excited state and will eventually move back down to their ground state During this de-excitation process, the electrons release back the energy they would have previously taken in This energy is usually transmitted in the visible region of the electromagnetic spectrum, thus generating the light observed in firework displays Since atoms of different elements are composed of different electron arrangements, with outermost electrons of different energies, the energy taken in to excite the outermost electrons varies. Hence, so does the energy which is emitted on de-excitation. This varying release of energy is observed as light of different wavelengths within the visible region of the spectrum; red light having the longest wavelength and the least energy, whilst violet light having the shortest wavelength and the most energy.15
More often than not, it is the positively charged (cationic) species in the compound which dictates the colour of the generated light. This species is written at the beginning of the chemical formula of the compound and may be in combination with a variety of anionic (negatively charged) species within the salt. Table 1 illustrates some compound and cationic precursors for different coloured lights 12,15
For example, strontium salts tend to generate red coloured fireworks whilst calcium compounds generate an orange colour. Furthermore, sodium is used for yellow, barium for green, and copper is used to produce blue coloured light. In addition to these compounds, mixtures of compounds may also be prepared to combine different colours and hence generate different secondary colours Although orange coloured light has calcium as a potential precursor, a strontium compound and a sodium compound can be used together so that red and yellow coloured light could be combined to generate orange coloured light A second example of these composite colours is the use of strontium compounds in combination with copper compounds to combine red and blue to produce purple.9,11,12,15
It is also interesting to note that certain chemicals used as fuels or oxidisers may also contribute to certain special effects seen in pyrotechnic shows. Whilst metals such as aluminium and magnesium are used as fuel, they can also be used to produce white smoke, or even gold sparks. In addition, bismuth oxide can be mixed with the aluminium-magnesium alloy magnalium to form a composition which produces a crackling effect. Equation 7 describes the reaction taking place.9,15
The Culture and History
Firecrackers fireworks were created by accident, like many other inventions Around 200 BC, the Chinese unintentionally invented firecrackers by tossing bamboo into fire, however, it took another 1000 years before true fireworks became a reality Around 800 AD, an alchemist mixed sulfur, charcoal, and potassium nitrate (which was used as a food preservative) hoping to find the secret to eternal life, instead, the mixture ignited. This is what we now call gunpowder. This powder could be packed into bamboo or paper tubes and lit on fire, and so were born fireworks that somewhat resemble those that we have nowadays In these times, paper fireworks were used to scare evil spirits or to celebrate weddings and births and were simply thrown onto a fire,
rather than being blasted into the air. There were no added colours, so a fireworks show was just a series of small, noisy explosions 16
If you had to attend a fireworks show in 1600, the science would not have been much different from ancient China, however, the entertainment factor was definitely greater. It became used for military victories, religious events, or royal celebrations, aerial fireworks (without added colour) were run by "firemasters" and their assistants, "green men"; named for the leaves they wore to protect themselves from sparks. Being a green man was a highly dangerous position, and many were injured or killed when their fireworks malfunctioned 16 Early U S settlers brought their love of fireworks with them to the New World and fireworks were part of the very first Independence Day; a tradition that continues every 4th of July.16 Nowadays, fireworks are used to mark major holidays, festivities and locally are synonymous with religious feasts
Fireworks in Malta have a long tradition which is centuries old The craft of pyrotechnics in Malta dates back to the time of the Hospitalier Order of the Knights of St John. The Order which was conventual, aristocratic and military oriented used to celebrate the most important feasts by special pyrotechnic displays Such firework displays were an expression of rejoicing on special occasions, such as the election of a Grand Master or a Pope, as well as on the birth of a prince and after victories of the Christians over the Ottomans. Pyrotechnics were probably inspired by cannon shots and musket fire. The feu de joie; a salute by the musketeers, produced a celebratory welcome to any dignitary. From this developed the musketterija which today is a series of hundreds of explosions of crackers firing in rapid succession. These are attached to a string placed on the roof top of a church or other large building 17,18
The solfarelli d'aria were a series of colourful weak shots fired in quick succession into the sky. The Jigjifogooh are a mechanised and rotating set of wheels attached to a pole on the ground which provide a rotating movement for the burning gas tubes This centuries-old tradition is still very popular in the crowded calendar of village feasts that take place all over Malta and Gozo, mainly during the summer months. There are around 35 fireworks factories and double that number of towns and villages where these displays are part of the traditional celebrations of patron saints 17
The Effects on Health and the Environment
Fireworks are in use worldwide, however their burning has been observed to have adverse effects on the environment An increase in chemical concentration of fine-mode particles was observed compared to the days leading up to the burning of the fireworks.19 The most common emission for the burning of fireworks is fine particulate matter, however other potential emissions include chlorates, dioxins or heavy metals 20 Fireworks and firecrackers contribute to air pollution, as when burnt, particulate matter is released, with studies showing that the particulate matter level increases significantly after a fireworks display. The particles remain suspended in the air, polluting the air, and increasing the risk of adverse health effects 21
Polymers are also emitted by fireworks, whereby they are emitted as projected debris that is released into the environment in an uncontrolled manner.20 In addition to the health risks that are associated with fireworks, they have great potential for wildfire and infrastructure fire ignition, and an extremely distressing effect on wild and domestic animals due to the loud noise the fireworks produce.22 Fireworks pollute water with a perchlorate, which contaminates the groundwater and surface water, which disrupts the thyroid gland in humans and has an impact on ecology 22 Similarly, toxic byproducts appear due to atmospheric reactions between metal oxides and organic fuels.
It is Maltese tradition to light fireworks at every feast, however the exposure to fireworks is so persuasive in Malta that perchlorate contaminates the water sources. Although the amount of perchlorate was found to be on the low side, it also contaminates soil and consequently contaminates the food grown on this contaminated soil, which can pose health risks. Perchlorate is more likely to be found in higher concentrations in dust, as it is stable, making it a persistent pollutant, but it is also water soluble.
This high amount of perchlorate is the result of intense and prolonged religious festivities all throughout the summer months, related to pyrotechnic activity, coupled with a territory size of limited geographical extent 23 Perchlorate (ClO4 –) is present in indoor dust in Malta where it appears to derive from the only source of contamination that is significant locally, namely, the burning of fireworks. Studies show that Malta’s perchlorate level is
almost double the amount of China’s. Dust is a significant source of human exposure to chemicals: the fine particulates present an inhalation risk, while coarser material is a risk for ingestion (Christoforidis & Stamatis, 2009; Shi et al., 2011), especially for infants and children who are more prone to transfer matter from hand to mouth. Contaminated dust fall also has potential to affect water quality and that of locally grown agricultural produce, which become potential sources for consumers of these foods.24
There are many other substances which were found to have elevated levels after a fireworks event, which come from the ignition of these fireworks These can have negative implications on the general health of those who are exposed to these substances. Respiratory symptoms such as chronic cough, phlegm and breathlessness are the most common symptoms observed and these exposures may increase the risk for respiratory diseases, mainly asthma and chronic obstructive pulmonary disease (COPD) 25
Asthma was observed to be caused or exacerbated by metallic particles in the smoke present after ignition of the fireworks. This was observed during a religious festival hosted in India called the Diwali festival in 2015, during which a multitude of fireworks were lit up After this festival, there was a 30% to 40% reported increase in worsening of bronchial asthma and bronchitis in patients of all ages and gender.26 This was also observed with COPD in another study in which it was stated that there was almost a doubling in intensified COPD cases for every 10 μg3 of increase in fine particulate matter (PM2 5) 27 However the effects of the particulate matter on human health is affected by many factors, such as its size, shape, concentration and chemical composition. There are two types of particulate matter, which are PM10 and PM2.5, PM10 having a diameter less than 10 μm whilst PM2 5 having a diameter less than 2.5 μm. PM10 is inhalable, however PM2.5 can get deep into the human lungs, and some can also enter the bloodstream, which can lead to even worse symptoms and diseases.28
Apart from particulate matter, there are many other substances which were found to be at an elevated level after ignition of fireworks, such as gases like sulfur dioxide and ozone. These have been observed to significantly increase asthma-related symptoms and to decrease lung function or cause pulmonary infections 29 Aluminium is used to produce silver and white flames or sparks, barium is used to produce green flames, cadmium is used as a universal colourant and copper is used to produce blue flames. These were all found at elevated levels after ignition of fireworks and studies have been performed on
their effects on human health. Inhalation of aluminium as fine powder could cause fibrosis in the lungs30 whilst barium was found to bind to DNA and kill to human lung cells and could also lead to pneumoconiosis in people with a high exposure to it.31 Exposure to respirable cadmium and copper was also found to cause harm to the lung tissue, especially by potentially causing emphysema or lung cancers 32,33
It can be argued that exposure to these dusts and gases are very much limited since fireworks are only ignited for a limited time, however it is found that particles can remain in significant concentrations in the air for up to 20 hours after the fireworks have been exploded 34 The people that are mostly exposed to these pollutants and particulate matter are the workers who produce the fireworks, therefore they should be careful of the time spent working, especially if no protective equipment is used such as masks or air filters
Apart from the respiratory effects, fireworks also have audible effects since the explosion causes a loud sound. Measurements taken from about a 100 m distance from the launch site show that fireworks could reach 100-125 dB with every explosion However, the World Health Organization suggests a limit of 80 dB to keep the human ear healthy,35 therefore it is suggested to wear ear protection when observing fireworks. The workers who ignite the fireworks are obliged to wear ear protection since the noise levels can reach up to 150 dB, which is very unsafe to the naked ear 36
Conclusion
To sum up, science and chemistry are useful tools when it comes to understanding fireworks and how they work From the redox and combustion reactions which propel and explode the fireworks, to the spectrochemistry that is involved in generating coloured light, all aspects are equally important to put up a pyrotechnic show in our skies However, one can truly hold an appreciation for fireworks only after looking through their rich history which spans the entire globe. It goes without saying that the possible and somewhat harsh effects on one's health and the environment cannot go unnoticed.
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