My 13-yr old son wants to make a homemade smoke bomb (with adult supervision). Your instructions seem to be the most detailed and thorough. But before conducting this home chemistry experiment, I want to be sure this can be done safely.
What are the risks/potential dangers associated with this procedure?
Is there any risk of the smoke bomb exploding, or igniting rapidly? Under what circumstances?
What should should we watch out for?
Also, where is the best place to buy a small quantity of potassium nitrate? Is it still available at most garden stores? Some stump removers use other chemicals; and some don’t list ingredients at all.
Any advice most appreciated!
Chevy Chase, MD
Smoke bombs are made by reacting potassium nitrate (saltpeter) with sugar over low burner heat. The project won't harm your cookware, plus the ingredients are safe enough that you can use the dishes you would use for eating, as long as you clean them. The MSDS for potassium nitrate provides handling and safety details, but I'll summarize the relevant points. Though potassium nitrate is found in some foods, you don't want to eat the pure powder. It's reactive, so it will cause itching and/or burning if you inhale any or get it on your skin. Potassium nitrate should be stored away from heat or flame. The chemical isn't flammable, but it's extremely reactive. Heat promotes reactions, which you don't want occurring on a shelf in your garage, for example. Follow the safety instructions on the container. If you get it on your skin, immediately rinse it off with water. If you spill potassium nitrate on the counter while making the smoke bomb, wipe it off with water.
You want good ventilation while heating the ingredients, as from a vented fan. An outdoor stove would be a good option. The big thing to watch for is spilling the mixture on the burner because it will catch on fire and smoke. If that happens, you'll get a lot of smoke and probably set off your smoke alarm. The smoke itself is no more or less dangerous than wood smoke, which means you don't want to take deep breaths of it. Ignite the smoke bomb outdoors. I can't envision a scenario where it would be possible to cause the smoke bomb to explode. How much flame you get depends on the potassium nitrate to sugar ratio. You can go from a smoky blob that will barely burn to a fast-burning fiery smoke bomb. If you set the smoke bomb on a combustible surface (like dried leaves), it could start a fire. If you need to put out the smoke bomb, you can douse it with water.
The hardest part about making a smoke bomb is finding the potassium nitrate. In some places, it may be sold next to epsom salts in the pharmacy section of a store. It is found in some garden supply centers as a fertilizer. It is sold as a food preservative for making salted meats. If you're highly motivated and have some time, you could even prepare it yourself. However, it's probably easiest to buy a small quantity online (e.g., Sargent-Welch). Supposedly some Indian food stores sell it as an ingredient named Kala Nimak. If you're in the UK, there is a forum discussion listing places that offer potassium nitrate. It's harder to find than in the past, not so much because it can be used to make gunpowder as because better products are available for most applications.
Make a Smoke Bomb | Make Green Fire
Photo: Homemade smoke bomb. (Timo Halén)