The introduction of alternate fuel vehicles leads to new safety challenges. This is particularly relevant in the case of hydrogen vehicles, as flammable mixtures of hydrogen and air can be very dangerous. Potential hazard scenarios include gaseous or liquid hydrogen leaks, accumulation and ignition of hydrogen clouds in partially confined and/or congested spaces (e.g., a vehicle's engine compartment), migration of air into systems containing pure hydrogen, or discharges from hydrogen storage tanks into parking garages or tunnels. Additional potentially hazardous hydrogen release scenarios may be associated with the hydrogen storage and delivery infrastructure - for example, storage tanks, trucks and refueling stations.
As for other flammable substances, standards are available that set safety requirements for hydrogen applications (e.g., NFPA 52, 55 and the soon to be released NFPA 2). In those documents, separation distances are specified for different types of application in order to protect the public and public property in the event of accidents. Given the broad scope of these standards, the separation distances are derived for ?standard? systems and conditions. When complex systems are being planned, or in ?crowded? areas, it is advisable to perform a site-specific study to determine the hazards from the new installation. An accurate hazard analysis requires a sophisticated tool to determine the consequences of a hydrogen release.
This paper describes a computational fluid dynamics (CFD) model ? FLACS ? that can be used to simulate the entire sequence of events following a hydrogen release: the pool spread and vaporization (in the event of a large liquid release), the dispersion of the hydrogen vapor cloud, and the propagation of the flame front and pressure waves following the ignition of the cloud. The paper will first provide an overview of the validation of FLACS against hydrogen dispersion and ignition experiments, then it will describe the application of FLACS to a set of realistic hydrogen release and ignition scenarios to demonstrate how a hazard analysis can be performed.
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