Cornstarch is a fine white powder you probably keep next to the flour in your pantry. Most people never think of it as a fire hazard — it's just a thickener for sauces and gravies. But cornstarch is actually one of the more dangerous combustible dust materials, more so than many people realize.
Cornstarch is flammable when dispersed as a dust cloud in air. As a solid sitting in a canister, the risk is minimal. But cornstarch particles are extremely fine, and when suspended in the air in sufficient concentration, they can ignite rapidly and cause a flash fire or dust explosion.
Why Cornstarch Is Particularly Dangerous
Cornstarch particles are exceptionally small — smaller than most other cooking powders. Smaller particles have more surface area relative to their mass, which means they oxidize faster and ignite at lower concentrations. The minimum explosive concentration for cornstarch is approximately 40 grams per cubic meter, similar to flour but achieved at lower particle concentrations because of particle size.
Industrial cornstarch processing facilities are subject to strict combustible dust regulations because of the documented explosion risk. There have been multiple industrial accidents involving cornstarch and similar starches. The Occupational Safety and Health Administration (OSHA) specifically lists cornstarch as a combustible dust hazard.
Kitchen-Scale Risk
At home, cornstarch is safe to use normally. You won't create an explosive dust cloud by spooning it into a sauce. The risk becomes real if you've ever blown a puff of cornstarch across a candle flame — you'll see a brief fireball. This is a well-known chemistry demonstration, and it illustrates how quickly fine particles combust when dispersed.
Keep cornstarch stored in sealed containers away from the stove. Don't use it near open flames. If you spill a large amount and it gets airborne, don't light anything nearby until it settles.
Cornstarch as a Fire Suppression Myth
Some people believe cornstarch can be used to put out fires. It cannot. Like flour, throwing cornstarch on a fire can make it dramatically worse. For small kitchen fires, use a Class K fire extinguisher or a metal lid to smother the flame. For more on what actually works, read our article on whether baking soda puts out fires.