The phenomenon of food dust explosions has only been recently discovered. Ones, it was a widespread belief that dust exploded because of the presence of alcohol or gas derived from the fermentation. Today it has been acknowledged that powders (depending on their granulometry) follow the same valid principles of gas and vapours. 

Analysis of the phenomenon

Three conditions need to happen so that an explosion occurs:

• presence of a combustive gas, even oxygen in the air;
• presence of a combustive product (in this case dust in the air);
• presence of an ignition source.

We can recognize in this list the famous “fire triangle” which highlights that an explosion is a particular case of combustion (an extremely fast combustion). However, with regard to dust, because this combustion could be classified as explosion, further three complementary conditions are required: 

• presence of dust in the air;
• a defined field of concentration;
• a sufficient confinement, otherwise there would be a flame phenomenon (rapid combustion with flame, but without any relevant pressure). 

In order to cause an explosion, the ignition source has to elevate the dust cloud temperature so that the oxidation, responsible for the combustion, could be produced at a sufficient speed. In case of electric ignition, the inflammable source could be a spark, a phenomenon of static electricity or a overheating area.

Standards

Cenelec issues a series of European standards in order to determine the features of cloud powders which may cause explosions:

• EN 14034-1:2004 – Maximum pressure of explosion determination
• EN 14034-2:2006 – Maximum speed of pressure increase determination
• EN 14034-3:2006 – Inferior limit of explosion determination LEL
• EN 14034-4:2004 – Concentration limit of oxygen determination LOC