Flour bomb
The classic high school flour bomb demonstration shows the explosive power of flammable powders under the right circumstances. Given a large enough suspension of combustible flour or grain dust in the air, a significant explosion can occur. For example, the 1998 explosion of the DeBruce grain elevator in Wichita, Kansas which killed 7 people. Photos here (http://www.wichita.gov/CityOffices/Fire/Photos/Gallery1.htm).