When a combustible dust is dispersed in air as a dust cloud, it has the potential to explode. An ignition source of sufficient energy or temperature will ignite the cloud and result in a rapidly expanding fireball. If the dust is burning inside an enclosure, pressure will increase rapidly to a maximum value. The maximum explosion pressure and pressure rise are both important characteristics of the material and can be measured in the laboratory by dust explosion testing.

Primary dust explosion video - custard powder
Shot at 600 frames per second, the video shows 1 gram of custard powder being dispersed in a glass tube past a hot coil ignition source.

Secondary dust explosion video - custard powder
Again shot at 600 frames per second, the video shows 0.5 gram and 1 gram of custard powder being disturbed by the same primary explosion and ignited.

There are many combustible dusts that will form an explosive atmosphere when dispersed as a dust cloud. Explosion prevention and explosion protection measures are required to control the hazard under European legislation (ATEX and DSEAR)