Fireworks have a certain aura about them. We look in awe at how so much color, fire and power can be harnessed and then released so violently yet artistically. Building an object capable of such energy does not bring thoughts of safety to the forefront of the average mind. Indeed there are some dangers involved. All of the dangers are however quite manageable with simple safety steps, and many can be prevented entirely. An individual who does not take shortcuts with safety will find building fireworks to be one of the most rewarding experiences to be found. It is not difficult to stay safe.
On the other hand, If an individual disregards basic safety, they will quickly find themselves at risk of dangers that they would not otherwise even need to consider. The steps to stay safe are very simple, and the extra time is not worth an injury.
The most important safety step is to start small. If you only work with as much composition as you need to complete the device you are currently making, and keep other compositions away from the area, not only would a mistake be less severe but it greatly reduces the chance of one happening. That also speaks to keeping your work area clean.
What may seem obvious but is easily forgotten or ignored, is to always work outside. When indoors, there are very limited routes of escape, the building itself could catch fire, there is low ventilation, and any chemical fire will be much more violent due to being confined. All of these dangers are solved by working outdoors. A single folding table placed away from any buildings is a great work area.
Something else to take much caution over is metal tools used. Some metals can spark in contact with other metal, or even worse it can cause static discharge on contact with just about anything. Some metal tools may still be used, but when they need to be brought near flammable materials they must be grounded first to get rid of any static charge. Anti-static spray is also useful to reduce this problem. Wear only cotton clothing when working with pyrotechnics, both to reduce static, as well as for fire protection.
A starting pyrotechnic should only ever make compositions that are known to be safe from a reliable source. Experimentation is best left to those with more experience. There are certain combinations of chemicals that are dangerous, some to the extent that they should not even be in the same room together. An inexperienced pyrotechnic however, does not require any of the chemicals that could be improperly mixed to form these dangerous compounds. An individual starting with simple black powder type chemicals (potassium nitrate, charcoal, sulfur and dextrin) does not need to worry about incompatibilities, but they must do research for every new addition to their chemicals.
When a new chemical with potential incompatibilities is added to a collection, never use the same tools with that chemical as you do with the counterpart in the dangerous mix, even if they have been washed. As a rule of thumb there should be a different set of tools for chlorates, perchlorates and nitrates. A beginner should only be using nitrates, but must remember this as the desire for more variety increases.
Some of the common incompatibilities to avoid:
Chlorates and sulfur or any sulfur compound (such as calcium sulfate)
Chlorates and phosphorus
Chlorates and ammonium perchlorate as well as other ammonium compounds
Chlorates in combination with metals and nitrates
Ammonium perchlorate and nitrates (this does not cause a particularly dangerous reaction, but it will ruin a composition)
As you can see, most of the dangers that come from improper combinations require chlorates. Chlorates are dangerous to begin with when compared to many other pyrotechnic chemicals, and therefore are rarely used. They should never be used by beginners.
The last thing I will touch on is the use of hot glue guns. Hot glue can be a very useful tool. On its own, hot glue will not ignite the vast majority of compositions on contact. The potential danger lies in the gun itself. Anything with electricity running through it has the potential to short circuit, and hot glue guns are no exception. Among firework builders there have been several known incidents where a glue gun has shorted out sending sparks into the work area. Obviously that results in a very dangerous situation. A solution to this problem has been to let the glue gun heat itself away from the work area, then unplug it and use while the glue is still hot. A short is then not possible while the gun is near any exposed compositions.