Hydrogen-air mixtures are flammable in a wide range of compositions and have a low ignition energy, compared to gaseous hydrocarbons. Due to its low density, high buoyancy, and diffusivity the mixing is strongly enhanced, which supports distribution into large volumes if accidentally released. Economically valuable discontinuous transportation over large distances is only expected using liquid hydrogen (LH2). Releases of LH2, at its low temperature (20.3 K at 0.1 MPa), have additional hazards besides the combustible character of gaseous hydrogen (GH2). Hazard assessment requires simulation tools capable of calculating the pool spreading as well as the gas distribution for safety assessments of existing the future liquid hydrogen facilities. Evaluating possible risks, the following process steps are useful:

1. Possible accident release scenarios need to be identified for a given plant layout.

2. Environmental boundary conditions such as wind conditions and humidity need to be identified and worst case scenarios have to be identified.

3. A model approach based on this information which is capable of simulating LH2 releases, vaporization rates and atmospheric dispersion of the gaseous hydrogen.

4. Evaluate and verify safety distances, identify new risks and/or extract certain design rules.

The process steps have been performed using the new validated 3D transient multiphase - multicomponent CFD model approach developed at Forschungszentrum Julich. A demonstration plant layout obtained from the IDEALHY project (Berstad et al.[1]) and two HAZID assessments (Hankinson et al.[2]) have been used for identifying a plant and a possible accident scenario. A general weather analysis at a possible location has been performed to identify weather conditions. Finally, a full transient parameter calculation has been set up, varying the LH2 release rate and the wind speed. The results have been analyzed and general conclusions have been derived.