Who could imagine New Year’s Eve or Independence Day without fireworks? Probably, everyone has seen fireworks in the night sky while some occasions. They are noisy but also spectacular at the same time. Have you ever wondered why once the fireworks are red or the others are blue or green? In this article, we are going to reveal some science behind fireworks.
This story of fireworks begins in the IX century in China when Choe Museon made the black powder which gave the beginning of fireworks and firearms. Initially, a powder was made from elemental sulfur, charcoal, and saltpeter. Over time producers start to modify the recipe to receive better, more colorful, and more spectacular effects that we know currently. The essential part of fireworks is called “pyrotechnic stars.” These little balls must contain a few necessary compounds like fuel, oxidizer, colorant, chlorine, and a binder. Fuel allows stars to burn but also allows some types of fireworks to fly. Each burning process needs oxygen to be burnt, and the oxidizer component provides that process. A significant part of each firework is a colorful light; it is provided by colorants far from pigments. The colors of fireworks are not there on their own or accidentally. Ions of various chemical elements cause the colors which we can see. These ions come from substances called salts. One ion has one characteristic color. By adding ions of specific elements and by mixing them, we can obtain each color we want [1].
Let’s take a look closer at the particular components of fireworks. Many substances used to make fireworks are quite reactive, so they are widely not added in their pure form, so that is why neutral and safe salts are so popular. Sodium and potassium as metals are very reactive, but in nitrates, they are less reactive. At the same time, while chemical reactions might be explosive, so that is why they are used in fireworks. According to the color – the yellow one comes from sodium ions, green ones come from barium ions, white from aluminum ions, while the copper stands for blue coloring. What about the other colors? The purple one is caused by potassium ions, red by lithium and/or strontium ions, while calcium ions cause the orange in the fireworks. Another chemical compound of pyrotechnic stars is chlorine. Producers use it to get a purer color. The last ingredient of fireworks is a binder, and it is used to glued ingredients together. Thanks to that component, the fireworks glow spectacularly in the sky [2].
Now we know how to obtain the color of fireworks, but fireworks must fly up and must have a necessary fire before we see it. The component that provides it is fuel. The most popular fuel in fireworks is the black powder, mainly made with three fundamental ingredients: coal, sulfate, and potassium nitrate. These substances are continuously used since the beginning of fireworks history [3]. Recently, the additional component added as a trace additive is a phosphorus. This substance is very reactive. When we have pure white phosphorus, it can ignite even after contact with the air. That is why only a tiny amount of such compounds are added inside. Fireworks are not the only place where we can find black powder. It is also in cartridges to firearms for its facile production. The following compound used to make fireworks is an oxidizer. This type of substance provides oxygen during a chemical reaction. That element is necessary for combustion. The packaging of fireworks is tight, so we cannot get enough oxygen from the air. Oxidizer solves the problem of producing the amount of oxygen required right in the burning place. Producers often use these substances as oxidizers- perchlorates, chlorates, nitrates, chromates, and oxides.
What about bringing all necessary compounds together? If they are not mixed well and not sealed, the reaction could take place too early and not work. The most common binders used are dextrin, resin, or gum-based compounds. When all ingredients are mixed together, they need a fuse to initiate the reaction by delivering the fire. There are a few types of fuses, depending on the purpose. We can find a volumetric fuse, detonating cord, and slow-burning fuse. The Visco fuse is very popular in fireworks and all pyrotechnics. It is a cord with the abovementioned black powder core. That type of fuse has four layers, where the first is a core, and the second is a thin cord tied around the center. The third layer is another cord but flows in another way. It prevents the fuse from unfolding. The last layer is nitrocellulose varnish. That solution prevents the fuse from getting wet and strengthens the structure.
That is it about the fireworks construction, but the end of their other faces. Fireworks are full of chemical compounds that are dangerous or toxic for human and animal health and the environment. Someone would say that only carbon dioxide (CO2) and carbon monoxide (CO) is produced while the combustion reaction is produced. First of them is a prevalent gas but also very dangerous for the environment. Carbon dioxide is the most important reason for global warming. The second of them is also hazardous gas but for the people’s health. Breathing in carbon monoxide is dangerous because it is associated with hemoglobin, binding it irreversibly much stronger than oxygen. When some person breathes in the CO for a long time or in high concentration, this situation would be dangerous for life because the body will not get enough oxygen. Each firework contains compounds reached in nitrogen, so there will arise nitrogen oxides. Then we can find two of them: nitric oxide (NO) and nitric dioxide (NO2). These gases occur in smog and are dangerous for health. Nitric oxide is a less toxic gas, which exists in the air for a short time because it goes to nitric dioxide very quickly. Nitric dioxide is a brown gas with a pungent smell. It is the main reason for smog’s color. It is irritating to the conjunctiva and mucosa of the nose and throat. Also, it irritates the respiratory system. Both NO and NO2 are responsible for acid rains [4].
The phenomenon of acid rain is dangerous not only for plants but also for buildings. It accelerates damage to buildings and the death of plants. Another substance which we can find among these gases is sulfur dioxide (SO2). It is also an ingredient of smog, and also it has a characteristic smell. In contrast to NO2, SO2 doesn’t have any color. Sulfur dioxide is a highly toxic gas with an acrid and suffocating odor and undergoes a series of chemical transformations in the atmosphere: it oxidizes to sulfur trioxide, which, as a result of reaction with water present in the air, forms sulfuric acid. Then it dissociates into ions like SO42- and H+. These compounds have a strong acidifying effect and are harmful to the environment in several ways.
Gases evolved from fireworks, while combustion is not the only problem. Another compound that can be released from fireworks is titanium dioxide (TiO2). This compound is generally safe, but when its particles have small sizes like microns or nanometers of titanium dioxide, it is dangerous for health. It can cause inflammation in the lungs, which can lead to fibrotic changes and proliferation. What about the metal ions from salts that were mentioned before? Well, all of them get to the environment. More spectacular fireworks are, more metals pollute the air and then also the water and soil [5].
Recent studies in German show that only during New Year’s Eve about 4,000 tons of dust get into the atmosphere. It equals to 15% annual issue of this dust by all cars in Germany. What about our lungs? It is better to do not stay outside while watching fireworks and even a few days after. Tiny particles released from fireworks and harmful compounds can increase the risk of many severe diseases and even cancer.
Summary
Fireworks are spectacular, and there are probably not many people who do not like them. They make our life a little bit of color and sparkle. At the same time, fireworks are also dangerous because of their explosiveness and because of substances that arise while burning them [6]. Fireworks are hazardous for health. Thus, the fumes get quickly to the environment and circulate in the ecosystem. Whenever you see fireworks in the night sky, better run; your lungs would appreciate it. Health first!
This article is a joint work of Jahub Hilus and Magdalena Osial from the Faculty of Chemistry, University of Warsaw as a part of the Science Embassy project. Image Credit – Agnieszka Pregowska
Bibliography:
[1] Fireworks shower the skies with science, Sid Perkins, 2019, https://www.sciencenewsforstudents.org/article/how-fireworks-shower-skies-science (accessed 21.07.07)
[2] What is in fireworks, and what produces those colorful explosions, Elizabeth K. Wilson, 2017 https://cen.acs.org/articles/95/i27/s-fireworks-produces-those-colorful.html (accessed 21.07.07)
[3] Fireworks: Pyrotechnic Arts and Sciences in European History, Simon Werrett, The University of Chicago Press, 1992
[4] The chemistry behind a fireworks explosion, Loren Grush, 2015, https://www.theverge.com/2015/7/3/8886697/the-chemistry-behind-a-firework-explosion (accessed 21.07.07)
[5] Smoke in the air: how fireworks affect air quality, Dudley Shallcross, Tim Harrison, 2012, 2011, Science in School, 21, 47-51
[6] Analysis of environmental impacts of combustion products of some pyrotechnic products, Bożena Kukfisz, Jakub Rakus, Robert Piec, 2019, Materiał Wysokoenergetyczne / High Energy Materials, 2019, 11 (2), 123 – 132