During World War II, as Hitler's air force kept bombing Britain, then bombs kept falling from the sky. The director of a flour mill in England was secretly glad that the bombs didn't hit his factory, but almost at the same time as the bombs were falling, there was a big explosion in the workshop itself, the roof flew up into the sky, and the power of the explosion far exceeded the destructive degree of the bombs. At the same time, there was another explosion in England towards the family flour mill.

For this peculiar explosion, not only make the factory losses, but also very difficult to doubt. Because there is no bomb fell on the plant, but also in the workshop only flour and machinery, there is no explosives such as explosives. Why this strange explosion phenomenon? After research found that the bomb's airwaves lifted the workshop flour dust, so that the air contained in the flour to reach a certain concentration, as long as the fire will explode. It turns out that the explosive is flour ah!

Perhaps, some friends will ask: flour and not explosives how it will explode? We know that the flour mill in the milling machine to process wheat into a very fine and very fine flour, the milling machine to consume electricity for the material being processed to do work, so that the material is crushed. Among them, part of the work done by the crusher is converted into energy, and stored in the material particles after being crushed after the surface, this part of the energy in the physical and chemical called "surface energy". For a certain substance, the greater the degree of pulverization, i.e., the smaller the particles, the greater the surface area, then the greater the surface energy. As an example, the surface energy of a 1 kg piece of silica is 0.2 joules, which is very small and equivalent to the work done to lift a 1 kg object 0.02 meters. However, if it is crushed into flour as fine as the dust, its surface energy up to 2.7 × 106 Joule, that is, equivalent to the same heavy object lifted 2700 meters by the work done, the surface energy has increased by 10 million times! It is because of the large increase in surface energy, which makes the material physical or chemical changes will release its energy. In this way, the flour is likely to explode.

In fact, the flour explosion as if by the high water than the low water has excess potential energy. Therefore, it is going to flow to the low place as well. So that in the flat into the seemingly insignificant fine dust as soon as they meet the right conditions, fully mixed with air, fire, it will rapidly undergo an intense combustion reaction, in an instant to release a huge amount of energy. As a result, the fear of things - flour explosion also happened.

In real life, not just flour, for those easy to ene burning dust such as cocoa, cork, wood, light rubber, leather, plastics, etc., as well as almost all organic compounds and a variety of inorganic materials such as sulfur, iron, magnesium, cobalt, etc. dust, if these dust in the air to reach a certain concentration, as long as the encounter with an open fire, even if it is a starburst, will also cause an uproar! - - A violent explosion occurs. And, sometimes these fine dust explosion is no less than the destructive effect of the bomb. For example, in 1846, Britain's Harwell coal mine had a big explosion. The famous scientist Faraday wrote in the report of this explosion: "The combustion and explosion of methane mixtures will set off all the coal dust that exists in the pit, and make it catch fire." It can be seen that the items that cause explosions are not explosives, and sometimes can not get people's attention to the object will also explode.