Flour explodes under certain conditions for two reasons. The first is that flour is a starch. Starches, like other carbohydrates, burn very easily. Secondly, while flour is not explosive in an inert state, it is capable of spreading in the air and creating a potentially explosive dust cloud. Flour explosions most often appear in locations where flour is heavily handled, although a small scale explosion can be created at home as well.

Flour is made from chains of glucose molecules, meaning that it is a complex carbohydrate. Although flour is not sweet to the taste, it does retain the highly flammable properties of sugars. However, flour will not ignite if it is densely packed, as it often is in a home kitchen. Flour must have ample air to explode, as might be the case in a flour mill when a tossed sack of flour splits open, for example.

For flour to explode, it must form a highly dispersed dust. Approximately two ounces (56 grams) of flour suspended in a cubic yard (one cubic meter) of air will have explosive properties. If a flame is introduced to the flour dust, the individual flour particles will burn. If the dust cloud is large enough, a flash fire inside the dust cloud will result, which can create a serious explosion.

Flour explosions are a much larger risk in areas where large amounts of flour are handled. Although a small dust cloud of flour might ignite in a home kitchen, the damage would probably not be severe. In a grain elevator or flour mill, however, the potential for a very large cloud of flour or grain dust is much higher. For this reason, care is taken in these facilities to prevent dust clouds, and potential sources of open flame are usually protected.

Some science classes create a small flour explosion to illustrate the principle. A simple and relatively safe way to do this is to light a candle inside a can with a lid. Poke a straw through a small hole drilled at approximately candle level, and puff flour into the can through the straw. A small fire should result, blowing the lid of the can off. If only a small amount of flour accomplishes this, the results of a larger flour explosion can easily be imagined.