Why does the flour mill hang a warning sign "No Fireworks" like a gas station? Answer with chemical knowledge

Flour is an organic matter, which is itself a barter. As we all know, if there are tiny particles in the matrix, their contact surface can reach the maximum accelerated reaction rate. There is also a lot of flour in the air of the flour mill, which has been fully contacted with oxygen. If they are ignited at this time, it will not only be as simple as burning air, but also may explode. So ... . .