In order to design commercially viable solid state hydrogen storage systems, it is important to understand and quantify the environmental reactivity of the active species in possible environmental exposure scenarios. This report gives a summary of standardized UN tests along with calorimetric experiments performed in order to quantify both the rate and the amount of the energy released; as well as characterize the reaction products resulting from water exposure of a lithium borohydride and magnesium hydride combination (2LiBH4 + MgH2).