The art of firework production has been around for many hundreds of years originating from China. There is no definite date but it is generally assumed that what is now referred to as black powder was discovered in an accidental circumstance. (https://www.fireworks.com/fireworks-university/history-fireworks/ accessed on 20th September 2017) this is believed to be during the song dynasty which was between 960-1279, around this time Chinese legend says that a cook accidentally mixed together charcoal, sulphur and saltpetre ( more commonly known as potassium nitrate, KNO3) these three ingredients became key to the whole industry we see today, for example in one new year’s eve firework show in London there could be up to £1.8 million worth of pyrotechnics using many tons of gunpowder (the guardian online, accessed 20th September 2017) all of which would not be possible if it wasn’t for this accidental discovery. The legend then continues to say that a few years later while experimenting Li Tan began to encase this new powder in bamboo tubes and throw them onto a fire essentially creating the first form of a firecracker, the Chinese celebrate this invention every year in the 18th of April by worshiping Li Tian as they are believed to ward off evil spirts. Gunpowder works on a chemical level because sulphur makes the powder simple to ignite, the charcoal acts as the fuel and then the nitrate wants to quickly get rid of its oxygen and therefore being a powerful reducing agent causes the mixture to burn at high speed, this is an extremely exothermic reaction and can create huge amounts of heat. The equation for this reaction is as follows;
10 KNO3 + 8C + 3S = 2K2CO3 + 3K2SO4 + 6CO2 + 5N2
Black powder has a rough explosive speed of 1,300 FPS, feet per second, which classifies it as a low explosive (to be a high explosive it must have a detonation velocity above 3,280 FPS) in terms of firework production this is considered an essential ingredient without substitute, however some people are trying to minimise its use in fireworks, the manufacturer standard fireworks have set to reduce its use by four fifths.
Gunpowder is imported mainly from Germany to create fireworks in the UK and this produces a large number of logistical challenges, being a powder it is easily ignited and creates an inhalation risk so much to the extent that several hundred people are estimated to die across the world due to accidents in this industry (the new scientist, https://www.newscientist.com/article/mg14018982-900-technology-plot-to-remove-gunpowder-from-fireworks/ accessed 20th September 2017) this replacement for gunpowder is a combination. Of Phenolic resin and potassium perchlorate, these two chemicals are slightly more complex to obtain but an advantage of this composition is being a resin compound it can be extruded. This means forcing the material through different shaped nozzles to create most shapes, this is used in other types of industry to make pasta or PVC tubing, this is a highly efficient process and in the production of gunpowder could save a lot of lives. Because this composition contains a resin it is much harder to ignite by accident like gunpowder is, this should aid the safety of what is portrayed as a very dangerous industry and rightly so, these compositions can be deadly if detonated on the ground in the mortar tubes. These tubes are used for the launch of firework shells, generally being made from PVC tubing again that has been specially reinforced to contain and direct the powerful lift charge upwards rather that outwards. A lot of research has gone into how to prepare lift charges to ensure they are not only safe but also give the highest possible break.
Firework shells are the most common form of aerial fireworks used on a commercial scale for large displays, they range in diameter and size but the majority being spherical due to the aerodynamic benefit of not having sides with more air resistance as can be the case in cylindrical shells. However each one does have its own advantages in the terms of cylindrical being able to hold multiple breaks for extravagant breaks, for example a 4 inch diameter cylinder cam have two separated compartments with different coloured stars, the base will be the primary burst as the shell is still rising with a secondary burst at the apogee of the shell, this cannot be achieved as easily with spherical shells and in addition to this a much more uniform break can be achieved with spherical shells. Cylindrical shells tend to drift in the air more than spherical shells due to their slightly less aerodynamic profile, this however does not mean they aren’t used, plastic cylinders are much easier to produce as they can be extruded and produced quickly and efficiently. They are measured in diameter of the cardboard or plastic hemispheres and the largest available to be bought by the public are 3 inch shells as they are considered to be safer. This is because the exploded diameter of the shell after breaking is roughly 125-foot radius at a height of 400 feet (http://www.jpyro.co.uk/?m=200706 accessed 21st September 2017) whereas bigger shells such as 10 inch shells burst with a radius 425 feet at 1075 feet in the air, if this was to explode on the ground there would clearly be a huge amount of damage and severe loss of life from the fragments of mortar tube and also the burning rock hard stars being launched at 1,300 FPS in all directions and burning at temperatures of 1,500 degrees centigrade (in the case of magnesium stars for a white effect) this is one particular area where the industry could be made more safe, for example the use of metal tubes for firing may cost more but at the same time will ensure more safety for the workers who assemble these shows or those who detonate them.
Shells take a long time to assemble but some can take much longer, for example up to 6 inch shells one layer of stars is used so there is only one effect created, these stars may have different layers of colour but only being one layer around the sphere makes them easier to produce whereas above this size 2 or even 3 layers can be used, these are called double petal shells, these shells are spectacular and due to the amount of materials required are expensive however this is generally a good sacrifice for the impressing of the crowd. The stars are placed with as few gaps as possible around the shell, this is because what may seem like a few millimetres inside the shell could leave a 10-meter gap when the stars have burst, this would not benefit the aesthetics of the product so care should be taken when loading shells not just to ensure that friction sensitive chemicals are not accidentally ignited which would result in a disaster and potential loss of life. After the stars have been successfully packed black powder coated rice hulls need to fill the shell as the bursting charge, this is advantageous over normal black powder as its not only lighter but burns slightly slower giving more of a powerful pushing explosive rather than a fast shattering explosion which would leave the stars broken up and unable to ignite. In terms of the lifting charge a similar principal is applied, if a high explosive was used the whole setup would shatter and the shell would be destroyed not only creating casualties but ruining the whole show, because of this a coarser powder needs to be used so it burns slower and again has more of a pushing effect, this needs to be even slower than the bursting charge however so 1 or 2 F black powder is used (the more Fs there are the finer the black powder is) which will be bigger clumps which results in a much slower burn. Some pyrotechnics have experimented with other lifting charges but none are as effective as black powder. (https://www.cannonfuse.com/store/pc/Pyrotechnic-Projects-Black-Powder-Manufacture-d7.htm accessed 21st September 2017)
Overall there is a lot of room for improvement of safety in this industry because any deaths at all should not just be accepted, it is true that most industries cause injuries each year but with number of several hundred per year this should be changed, the resin mentioned earlier that could be in place black powder could be a good start but it currently has not been scaled up and used on anything apart from small samples and batches so only time will tell how effective this will be on a large scale. In my opinion, there is room for improvement here but it must be kept in mind there are thousands of shows around the world each year so major companies looking to maximise profits will use cheap labour and this causes a number of health and safety issues, this arguable should not be the case but something that is engrained in the industry will be hard to change.
References
• The pyrotechnics treasury book, by Thomas Kentish first published 1878
• A professional’s guide to pyrotechnics, understanding and making exploding fireworks, John Donner1997
• New scientist online accessed 20th September 2017
• Cannonfuse.com guide to making large Ariel shells, accessed 21st September 2017
• The guardian online