This doctoral study investigates and closes a number of knowledge gaps identified in hydrogen safety engineering and associated with the employment of high pressure storage systems. Analytical and Computational Fluid Dynamics (CFD) models were implemented and developed to assess the hazards from catastrophic failure of high-pressure hydrogen storage, i.e. an event concerning "failure of a vessel so severe to necessitate replacement or major repair" (Smith and Warwick, 1983). The developed models were validated against experiments. Parametric studies were conducted where relevant to provide insights into the investigated phenomena and into the effect of sub-models and parameters, identifying appropriate numerical requirements for such modelling studies. In case of release from a damaged tank or a Thermal Pressure Relief Device (TPRD), hydrogen is likely to ignite producing a jet fire, causing life-threatening conditions by the flame length and thermal radiation. A predictive CFD tool was developed and validated against experimental tests on hydrogen jet fires from several storage conditions, i.e. low temperature (48 K) and high pressure (900 bar). However, ignition delay of the jet may occur which produces a significant overpressure. Numerical simulations were conducted to investigate the formation of the turbulent non-uniform mixture and subsequent ignition for 200 bar and 40 bar releases. Two CFD approaches were proposed and their response tested. A numerical study was conducted on ignition of a quiescent hydrogen-air mixture by spark discharge. The study provided insights into the flame kernel formation and propagation. A contemporary tool was developed for numerical evaluation of Minimum Ignition Energy (MIE). In case of a continuous and/or established fire involving the tank, the TPRD activates venting the gas and preventing the catastrophic rupture of the tank. If it fails to activate and no adequate thermal protection is provided, the tank can catastrophically rupture with devastating blast wave and fireball. A CFD tool was developed to predict the associated hazards and it was validated against experiments on rupture of 70 MPa tanks.