Flour is the term used for the powdery substance resulting from the grinding, milling or pulverizing of grains, seeds, roots or other edible materials. Wheat, rye, oats, rice, corn, taro root, and cassava are some examples of grains and roots that are ground into flour, primarily for baking. Flour is the main ingredient in bread, which is a staple food in most cultures.
In common usage, flour refers to wheat flour. Wheat grains are composed of a starchy inner portion, called the endosperm, which makes up 85% of the grain kernel; the outer layers, known as bran, and the oily wheat germ comprise the remainder. The milling process separates out the endosperm and reduces it to fine particles.
While generally innocuous in itself, soy flour, oat flour, potato flour, rice flour, rye flour and wheat flour are all classified as “combustible dusts” by the United States Occupational Safety and Health Administration and the handling of these flours is subject to standards used by this agency to mitigate the risks of dust explosions.1 There is an average of ten wheat grain mill explosions in the United States per year,2 some with devastating consequences. These explosions are usually caused by the presence of a “fire triangle,” that includes oxygen, an ignition source and a fuel, such as flour dust.