This paper aims to develop quantitative insights based on measured deflagration parameters of hybrid mixtures of activated carbon (AC) dust and hydrogen (H-2) gas in air. The generated experimental evidence is used to reject the claim of the null hypothesis (H-0) that severity of deflagrations of H-2/air mixtures always bound the severity of deflagrations of heterogenous combustible mixtures of AC dust/H-2/air containing the same H-2 concentrations as in the H-2/air binaries. The core insights of this investigation show that the maximum deflagration pressure rise (Delta P-MAX) and maximum rate of pressure rise ((dP/dt)(MAX)) of this hybrid mixture are greater than those corresponding to deflagrations of H-2/air mixtures for all the dust and H-2 concentrations being examined. The deflagration severity indices (K-st and ES) of the hybrid mixture containing 29 M01% H-2 are found to be greater than those of the H-2/air mixture containing 29 mol% H-2. Also, the minimum explosible concentration (MEC) of the hybrid mixture is lower than that of the AC dust in air only. The insights gained should lead to better realization of the severity of a postulated safety-significant accident scenario associated with on-board cryadsorption H-2 storage systems for fuel-cell (FC) powered light-duty vehicles. The identified insights could also be relevant to other industrial processes where combustible dusts are generated in the vicinity of solvent vapors. Moreover, these insights should be useful for supporting quantitative risk assessment (QRA) of on-board H-2 storage systems, designing improved safety measures for cryoadsorption H-2 storage tanks, and guiding H-2 safety standards and transportation regulations. (C) 2013 Elsevier Ltd. All rights reserved.