Considering of numerous advantages of the Underground Hydrogen Storage (UHS), such as high energy density, low leakage rates and great storage volume, risk analysis of UHS is a required step for assessing the suitability of this technology. Different hydrogen storage options are available, but salt caverns are considered the most promising solution because of the favorable mechanical properties of salt that guarantees long term stability and the tightness of storage.

Typical conditions of underground hydrogen storage in salt caverns are high pressure (50-150 bar), mild temperatures (30-40°C). At these conditions, bacterial metabolism in the deposit may activate the conversion of hydrogen (H2) to methane (CH4), and methane to hydrogen sulfide (H2S), which is toxic and corrosive.

In case of rupture at the ground of the riser pipe from the salt cavern to the ground (worst-scenario), several hazards may arise due to the flammable nature of H2 and CH4 with the formation of jet fire and/or Unconfined Vapor Cloud Explosion (UVCE), or the dispersion in the environment of a gas mixture containing H2S. In this preliminary work, the analysis of the consequence due to the release in the atmosphere of pure H2 from riser pipe was carried out.

The dispersion of hydrogen in the environment was analyzed by Computational Fluid Dynamics (CFD) simulations while the possible consequences were evaluated by empirical models. The results show that the explosion is the most frequent outcome with a fatality level of 50% at about 38m from the source.