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.