Extremely Hazardous
Any Ammonium compound combined with any Chlorate compound
(NOTE: The ammonium chlorate risk is so hazardous that even stars with ammonium and chlorate compounds located in different layers should be avoided. Chlorate and Ammonium should never co-exist in the same shell or even in the same workshop. If you use Ammonium Perchlorate (AP) compositions, then you would do best to just avoid chlorates altogether, and vise versa. You can choose the vibrant colors offered by AP or the ease of ignition and brilliant light output offered by chlorates, but don't be tempted to manufacture both under the same roof and definitely don't combine both into the same device)
Chlorate and zirconium
Chlorate and red phosphorus
Hazardous
Chlorate and any Sulfur, Sulphate or sulfide compounds
Chlorate and dark aluminum
Chlorate and Antimony Trisulfide (increased friction sensitivity)
Chlorate and Magnesium powder
Chlorate and Titanium (increased friction and impact sensitivity)
Chlorate and any chromium or chromate compound
Chlorate and any metal powders (some already listed)
Chlorate and any metal oxide
Chlorate and lampblack (due to sulfur content)
Chlorate and any hydrocarbon fuel
Chlorate and napthalene
Chlorate and Realgar
Potassium Chlorite impurities in a chlorate compound that exceeds .001%
Potassium Chloride impurities in a chlorate compound that exceeds .08%
Mildly Hazardous
Chlorate stars primed with black powder
Chlorate stars in a shell with a burst charge that contains sulfur
Chlorate burst charge in a shell with black powder primed stars
Process Reactions
Some chemical combinations might be fine by themselves, but become reactive when a third element such as water, heat or sunlight is introduced during the manufacturing process. The most common reactions are listed below:
Magnesium-Water: this is a very reactive combination that will generate heat to the point of combustion. Compositions containing magnesium powder must never be bound by water. The magnesium must also be coated with a protective barrier even when bound by other solvents such as acetone or NC lacquer. More on this subject can be found here.
Aluminum-Nitrate-water: Any composition containing the commonly used nitrate compounds along with a finely powdered aluminum will be subjected to an accelerated reaction in the presence of water. This reaction will generate heat, which acts as a catalyst to speed the reaction even further, and thus generating even more heat. This heat can easily build up to the point of igniting the composition. The reaction often gives off an odor that can help alert you to the danger. Sometimes the reaction will start to occur during the mixing stage when dampening the composition, since it is in one large clump that traps the heat inside. If you feel the composition gradually warming, spreading it out into a thin layer on a pan will often dissipate enough heat to stop the reaction. The temperature at which the reaction rapidly accelerates is about 176 degrees F. If the temperature of the composition progresses beyond warm during mixing, quickly move it to a safe place outdoors where it can safely ignite without damaging anything.
Aluminum-nitrate reactions can be suppressed with the use of boric acid in order to keep the PH levels around 4.7 to 5.1. The boric acid is often included in the formula for mixtures that are prone to this reaction, but it is more effective if it is dissolved into the water used to wet the composition rather than screening it into the composition itself. Even with the boric acid, aluminum-nitrate stars should always be dried outdoors (in the shade) until you have enough trials to determine if the reaction is prone to occur or not.
Chlorate-tap water: when wetting a chlorate formula with water for binding stars, it is best to use distilled water in order to avoid the presence of iron or calcium carbonate that can sometimes be found in hard tap water. Well water should have a PH close to 7.0 if used.
Chlorate-sunlight: The ultraviolet rays of strong sunlight are capable of decomposing potassium and barium chlorate compounds, which increases their sensitivity. If the composition contains sulfur compounds, any sulfuric acid that forms due to contact with moisture can break the chlorates down into chlorine dioxide, which is decomposed explosively by sunlight. The chlorine dioxide will break down into chlorine and oxygen, which will then ignite any combustible material it contacts.
Friction Sensitivity
Most of the hazardous combinations seen above are the result of an increased sensitivity to friction. The amount of energy it takes for any given composition to initiate the decomposition reaction of the oxidizer and the reduction reaction of the fuels is known as the activation energy. Normally we supply all of this energy in the form of heat when we ignite the material with an open flame or spark. However, this energy can be transferred into the material in ways other than heat alone. The two most common alternatives are friction and shock, with friction being the most common problem.
In case you didn't notice, chlorate is present in every hazardous combination listed above. Chlorate molecules have three loosely bound oxygen atoms that are easily given up during reactions, a process known as decomposition (or "burning" in pyro terms). The fact that the bonds of these oxygen atoms are so easily broken is what accounts for the lower activation energy of chlorate compounds. Perchlorate compounds, by comparison, have four oxygen atoms that are tightly bound, thus it takes more activation energy to start the reaction. This is why perchlorate formulas have a higher ignition point and burn at a slower rate than chlorates.
So not only do chlorate compounds ignite at lower temperatures (which is actually a benefit when you are trying to avoid blind stars), but it also takes less friction to trigger a reaction compared with other oxidizers. Common sources of friction include stars scrapping against each other when loading them tightly into a shell, composition getting pinched between the threads of a lid when screwing the caps on containers, dragging containers and other objects across loose composition that was spilled on a table or floor or scraping a scoop against the bottom of a container when scooping a sensitive composition.
Every composition has an activation point where a given amount of friction will trigger the reaction, regardless of what oxidizer is used. However, this trigger threshold is much higher on some oxidizers than others, such that you would not likely be able to ever generate that much friction with the typical operations being performed. Even something as friction intensive as ball milling is not enough to trigger the threshold for black powder, whereas it would easily set of a chlorate mixture.
Avoiding friction is a good practice regardless of what chemicals you are using. Avoiding compositions that are sensitive to the amounts of friction you are able to produce unintentionally such as by a slipped screwdriver, dropped shell or sliding container is an even better idea.
For chlorate fans who don't want to give up the bright colors, easy ignition and resistance to blind stars, your formulas can be made less sensitive by following this tip from the Russian chemist A. A. Shidlovskiy: adding non-chlorate oxidizers to any formula containing chlorates will decrease the overall sensitivity of the mixture. This difference can often be dramatic when the chlorate compounds make up less than 50% of the total oxidizer component. If you ever see a chlorate formula that contains other oxidizers and were wondering why they are there, this is the most likely reason. The overall activation energy of the mixture is being raised in order to lessen the sensitivity to friction, while still gaining some of the benefits of using chlorates such as good colors, brighter intensity and lower ignition temperatures.
Shock Sensitivity
Shock is another form of mechanical energy input, just like friction, although it is less problematic due to the circumstances required to produce it. Dropping a hammer down on a pile of composition laying on the ground is an example of shock, whereas dragging the hammer across the pile would be friction. About the only common operation that produces shock is hand ramming with a rod and hammer. Once again, chlorates are at the top of the list for shock sensitivity. It goes without saying that chlorate mixtures should never be rammed into a tube or subjected to any similar type of impact. This is a pretty easy one to avoid. You just don't do it.
Perchlorates can take a lot more shock than chlorate mixtures, but again you may be flirting with that fine line. You may be able to get away with hand ramming a perchlorate mixture 200 times, but that one time it goes on you is all it takes.
Black powder mixtures can be pounded all day long without worry however, which is why they make such ideal rocket fuels. About the only way you could ever reach the activation energy of black powder would be if you managed to create shock, friction and heat all at the same time, such as if a bit of composition sitting on the tip of a bent rocket spindle was pinched between the rammer right at the time of impact. Even this would be a freak accident with a very low probability of occurrence.
Pressing is the safest way to consolidate any pyrotechnic mixture into a tube, since the gradual increase of pressure does not produce any shock forces.
Pressing is the only method that should be used for whistle rockets and other perchlorate mixtures that need a strong degree of consolidation.
Some mixtures, such as strobe rocket mix, have been known to ignite even when pressed into a tube. Thus care must be taken to know the nature of the
formulas you are delaing with before working with them. A polycarbonate blast shield (which won't shatter like acrylic) should be a fixture
on every pressing station, along with the use of safety goggles by the press operator.
Static Electricity
Some pyrotechnic mixtures are prone to ignite from static electricity, especially those that contain metallic powders. Even some mixtures that contain no metal at all are still prone to static ignition, such as whistle mix. Flash is one of the more sensitive mixtures, and also the most destructive should even small amounts accidentally ignite.
The best way to eliminate static electricity is with humidity. When the air is humid, water molecules collect on the surface of your skin and other objects, which prevents the buildup of static. The drier your skin is, the easier it will hold a static charge. A good rule of thumb is to stay away from contacting pyrotechnic mixtures when the humidity drops below 50%. You should keep a humidity gauge in your shop for monitoring this percentage. Radio Shack sells such a gauge that reports both humidity and air temperature.
Since cold weather usually brings drier air, humidity levels will be at their lowest during the winter. For Northern states or desert environments, the low humidity in winter months can be a real static risk. Tropical environments like Florida have almost no static problems at all, which may be why several fireworks manufacturers are located there.
There are several precautions that can be taken to minimize the risk in a static prone environment. Many techniques have been developed in the electronics industry to deal with the destructive problems caused by static, and these can be applied to a fireworks shop as well. The trick to getting rid of static is to conduct it away to somewhere else. There is conductive paint that can be used to paint the floor of your shop. A grounded touch pad can be placed at each entry point so that a person can discharge themselves upon entering the work area. Ground straps can also be worn on the wrist, which make a connection from a metal contact point on the wrist strap to a grounded connection on your bench via a long wire. Conductive frocks made from a special material can also be worn to keep charges from building on your clothes.
Using metal scoops also helps eliminate static buildup when transferring mixtures. If you have ever seen red gum align itself in a plastic scoop like steel filings around a magnet, you have seen how easily fine powders can generate a charge on plastic surfaces.
