In order to prevent dust explosions due to electrostatic discharges (ESD), this paper reports the minimum ignition energy (MIE) of aluminum powders in the air and the effective nitrogen (N-2) concentration for the inert technique. The Hartman vertical-tube apparatus and five kinds of different sized pure aluminum powders (median particle size, D50; 8.53 mu m-51.2 mu m) were used in this study. The statistic minimum ignition energy (MIEs) of the most sensitive aluminum powder used in this study was 5 mJ, which was affected by the powder particle size (D50; 8.53 mu m). In the case of aluminum powder, the inerting effects of N-2 were quite different from the polymer powders. The MIE of aluminum powder barely changed until the N-2 concentration was 89% in comparison with that of the normal air. When the N-2 concentration was 90%, the MIE of aluminum powders suddenly exceeded 1000 mJ, which does not occur easily with ESD in the industrial process. (c) 2015 Elsevier Ltd. All rights reserved.