The thermal behaviour of two different Al nanopowders and a micron-sized Al powder was studied using DSC, simultaneous TG-DTA, and accelerating rate calorimetry (ARC). The results show that the reactivity of Al powder increases as the particle size decreases. The thermal stability of the smaller Al nanopowder (Als) in water and in a humid atmosphere was determined using ARC and TG-DTA, respectively. Atomic Absorption Spectrometry (AAS), X-Ray Photoelectron Spectrometry (XPS) and Auger Electron Spectrometry (AES) were used to characterize the surface chemistry of Alex. The outgassing behaviour for mixtures of RDX and the various Al powders was investigated using TG-DTA-FTIR-MS. Evolution of NO2 and N2O from a chemical interaction between Al nanopowders and RDX was observed. The effect of Als and Alex on the thermal stability of TNT, RDX, Comp 13, and AP was determined using ARC. Addition of Als significantly lowered the onset temperature for TNT and RDX decomposition. Electrostatic discharge (ESD) sensitivities of Al nanopowders and their mixtures with TNT, Comp B, RDX and AP were determined. The results show that the AP/Als mixture is very sensitive to ESD. Standard dust explosibility tests demonstrated that Alex is highly explosible.