Experimental and theoretical studies were conducted to investigate the pyrophoricity and water-reactivity risks associated with employing sodium alanate (NaAlH4) complex metal hydride in on-board vehicular hydrogen (H-2) storage systems. The ignition and explosivity of NaAlH4 upon exposure to oxidizers in air or water were attributed to the spontaneous formation of stable hydroperoxyl intermediates on the NaAlH4 surface and/or H-2 production, as well as the large driving force for NaAlH4 conversion to favorable hydroxide products predicted by atomic and thermodynamic modeling. The major products from NaAlH4 exposure to air: NaAl(OH)(4), gibbsite and bayerite Al(OH)(3), and Na2CO3 observed by XRD, were identified to be formed by surface-controlled reactions. The reactivity risks were significantly minimized, without compromising de-/re-hydrogenation cyclability, by compacting NaAlH4 powder into wafers to reduce the available surface area. These core findings are of significance to risk mitigation and H-2 safety code and standard development for the safe use of NaAlH4 for on-board H-2 storage in light-duty vehicles. (C) 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.