A dust explosion is the rapid combustion of fine particles suspended in the air. Dust explosions can occur where dispersed powdered combustible material is present in high enough concentrations in the atmosphere.
This is what happened this weekend in Taiwan: http://www.cnn.com/2015/06/28/asia/taiwan-water-park-explosion/
For a comparison see what happens with a right mixture of otherwise benign creamer powder and air: https://www.youtube.com/watch?v=yRw4ZRqmxOc