Experimental investigation of the complex deflagration phenomena of hybrid mixtures of activated carbon dust/hydrogen/air

• Improved understanding of severity of deflagrations associated with activated carbon dust/H2/air hybrid mixtures.
• Determined deflagration parameters of activated carbon/H2/air hybrid mixtures for H2 storage systems in light-duty vehicles.
• Established new deflagration parameters to supplement missing data in materials safety data sheets (MSDS).
• Generated new deflagration data of significance to hydrogen safety standards and to OEMs of H2 storage tanks.
• Quantified deflagration parameters to guide hazards assessment, risk mitigation, and protective components design.

This paper aims to develop quantitative insights based on measured deflagration parameters of hybrid mixtures of activated carbon (AC) dust and hydrogen (H2) gas in air. The generated experimental evidence is used to reject the claim of the null hypothesis (H0) that severity of deflagrations of H2/air mixtures always bound the severity of deflagrations of heterogenous combustible mixtures of AC dust/H2/air containing the same H2 concentrations as in the H2/air binaries. The core insights of this investigation show that the maximum deflagration pressure rise (ΔPMAX) and maximum rate of pressure rise ((dP/dt)MAX) of this hybrid mixture are greater than those corresponding to deflagrations of H2/air mixtures for all the dust and H2 concentrations being examined. The deflagration severity indices (KSt and ES) of the hybrid mixture containing 29 mol% H2 are found to be greater than those of the H2/air mixture containing 29 mol% H2. 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 cryoadsorption H2 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 H2 storage systems, designing improved safety measures for cryoadsorption H2 storage tanks, and guiding H2 safety standards and transportation regulations.