Lefty's Mixing Shed

The destructive potential of flash powder should not be under-estimated. More serious injuries probably have been caused by flash powder than practically anything else in the world of pyrotechnics (including black powder).

Let's not kid around here. Good flash powder has explosive potential rivaling high explosives (such as TNT). Even a seeming small amount (a few grams) in the hands of child or inexperience pyro can have disasterous consequences. Larger amounts (10's or 100's of grams), which are typical for inexperienced pyros who don't know the real hazards, often are lethal when things go wrong. What can go wrong? PLENTY!

First of all, most flash powders are friction sensitive. The most common flash powder is 70:30 KClO4/Al. Many pyros add an additional 10 pts (by wt) of S. If your KClO4 is very fine and you are using a high quality Al powder (e.g., German or Indian dark Al), the explosive potential of your mixture is downright scary. The addition of S (or antimony sulfide) makes the mixture even nastier and more friction sensitive. You should treat these mixtures with great respect and assume that any screw-up will be devastating.

What are the hazards?

(1) Good flash powder is friction sensitive. One of my friends, who is an established rocket maker, learned this the hard way during the first year or two of his pyro career. When he was 17 years old, we was mixing flash powder ingredients in a mortar and pestle. Approximately 25-50 grams exploded during "gentle grinding". My friend now has a deformed hand and is lucky he didn't lose several fingers (or his life!). Years later, this same friend was the Safety Chairman at a fireworks convention in the US. During this convention, one of the attendees - who was as relatively experienced pyro - tried to dispose of approx 1 lb of flash powder by spreading it on the ground in the Arizona desert. When this attendee tried to mix/bury the flash powder with sand using his foot, the powder detonated. The poor guy lost most of his foot, even though he was wearing heavy boots. My friend found two of the missing toes and was reponsible for seeing that everything made it to the hospital.

(2) Flash powder is very static sensitive. If you are working in an environment with fluorescent lights, open electical outlets or very low humidity, it doesn't take much to create a spark sufficient to cause an explosion.

There are many other hazards. The key to avoiding disaster is to understand them and religiously avoid known mistakes. Bill Ofca's "Technique in Fire", VOl 1, should be required reading for anybody thinking about working with flash powder.

Over the years, I have mixed hundreds of pounds of flash powder. I've never had an accident, but I still get a little nervous every time I do it. My favorite formula is 70:30:10 KClO4/Al/S for smaller salutes (up to 70 g) and 70:30 KClO4/Al for larger salutes or bottom shots. As a youth, I tried many of the other formulae listed in older books (e.g., T. L. Davis, Weingart, Kentish, etc.) I now know that many of these formulae are both much more dangerous and much less effective. My advice for pyros is to stick with 70:30 KClO4/Al for flash powder.

A few comments:

(1) Work with small quantites, especially if you are relatively inexperienced. An accident with several grams of flash powder will be ugly enough. An accident with 500 grams is likely to be fatal.

(2) Try to work when relative humidity is >60%. Work outside in natural light w/o direct sunlight. Work away from light fixtures, receptables and any potential source of spark or ignition (e.g., cell phones, electic motors, cigarettes, high power lines, etc). Avoid tools, containers, hard surfaces and actions that can cause enough force or friction to ignite flash powder.

(3) Bill Ofca advocates ball milling to make fine powders. I like to use a blender. (Powdered sugar can be made by pulverizing common sugar in a high-speed blender. The same technique can be used to make fine powders from many other materials. NEVER PULVERIZE ANYTHING OTHER THAN SINGLE CHEMICALS IN A BLENDER. Numerous people have been killed by mixing pyro forumations in blenders, coffee grinders, etc.)

KClO4 for flash powder can be prepared ahead of time as a free-flowing, fine powder by powdering KClO4 with 0.1 wt% Cabosil in a blender. Approximately 300-500 grams typically can be prepared at a time. Store in an air-tight container, and allow the material to cool to room temperature before using. (Grinding in a blender creates lots of heat.)

The characteristic smell of hydrogen sulfide (i.e., H2S) can be detected at remarkably low levels (i.e., parts per billion in air). If the smell is slightly offensive and it doesn't get worse with time, you're normally okay. If the smell is downright overpowering or seems to be getting stronger over time, it's probably best to dispose of the offensive material. Fireworks compositions aren't supposed to evolve large amounts of H2S. If yours does, there is something wrong.

A word of caution: Your ability to smell H2S is compromised as you smell H2S. The best way to know whether the smell is getting stronger or weaker is the leave the area for a few mins and re-enter.

Commercial wheat past is sometimes hard to find, but homemade paste is easy to make. Bill Ofca provided a procedure in one of his "Technique of Fire" books, and I modified it to avoid lumps: Bring 9 cups of water to a rolling boil. In a blender, add three cups of cold water followed by 2 cups of all-purpose flour. Quickly put the cover on the blender and start the blender on a medium setting. After about 20-30 seconds, stop the blender. This will release a strange air bubble that seems to form in the flour mixture. Start the blender again, and then mix for another 30 seconds while using a spoon to carefully dislodge any wet flour clinging to the blender's container. Quickly add the flour mixture to the boiling water and immediately start to stir the hot mixture. An electic mixer works very well for this purpose. As the mixture comes to a boil, reduce the heat. Mix/stir for another minute, then turn off the heat and mix/stir for another minute. (This avoids having the bottom burn or cook much more than the rest.) Cover the pot and set it aside to cool for several hours. Paste prepared in this manner will spoil within a couple of days in warm weather, but its pot-life can be extended by adding a small amount of boric acid or salicylic acid.