An experimental investigation was carried out on the influences of dust concentration, particle size distribution and humidity on aluminum dust explosion. Tests were mainly conducted thanks to a 20 L explosion sphere. The effect of humidity was studied by storing the aluminum particles at constant relative humidity until the sorption equilibrium or by introducing water vapour in the explosion vessel. The tested particles sizes ranged from a volume median diameter of 7 to 42 mu m and the dust concentrations were up to 3000 g m-3. Among other results, the strong influence of the particle size was pointed out, especially when the Sauter mean diameter is considered. These results stressed the predominance of the specific surface area on the mass median particle diameter. The effect of water on aluminum dust explosion was decoupled: on the one hand, when water adsorption occurs, hydrogen generation leads to an increase of the explosion severity; on the other hand, when the explosion of dried aluminum powder occurs in a humid atmosphere, the inhibiting effect of humidity is put forward. A model based on mass and heat balances, assuming a shrinking core model with chemical reaction limitation, leads to a satisfactory representation of the pressure evolution during the dust explosion. (C) 2009 Elsevier Ltd. All rights reserved.