An explosive atmosphere is any mixture, under atmospheric conditions caused by the handling or storage activity, of air and flammable substances in form of gas, steam or dust in which, after ignition, the unburned mixture is propagated.
Small particles coming from wheat flour, sugar, starch, cereals, milk powder in the food industry can be a danger because they have a high explosive potential. Also the aluminum powder, brown coal, iron powder, wood dust, soot, sulfur have this same problem if they join the circumstances that can lead to a catastrophic explosion.
For this type of environment, fans installed both for air supplying and extracting must be ATEX certified. Industrial fans are protected against explosion by the use of aluminum or copper inlet rings, EEX motors and special coatings.