Assessment of damage to people and buildings as consequence of hydrogen pipeline accidents

Hydrogen is increasingly considered a valid alternative to traditional fuels, which are gradually being more and more depleted. It is defined as “the energy carrier of the future” and so, as such, it must be produced. Several hydrogen production technologies are widespread and they involve both traditional and innovative sources. After its production, the hydrogen must be made available for use and, so, it must be transported from the production site to the utilization site. One of the most common ways to transport considerable quantities of gaseous hydrogen is through pipelines. Since hydrogen is considered a “no safe” fuel due to its physical properties, the consequences of an accidental release must be investigated, to preserve the safety of people and facilities located in the surrounding area of a possible accidental event involving pipelines. Hydrogen disperses into the air very easily, being lighter than air, but if it is released in a confined space can result in an explosion. The hazards of the hydrogen-air mixture are related to the wide flammability range and the low minimum ignition energy. Furthermore, hydrogen burns with an invisible flame and so it is very difficult to suddenly identify the presence of danger. Based on these considerations, it results that a failure of pipeline conveying gaseous hydrogen can pose severe risks. The aim of this study is to evaluate damage to people and buildings involved in high-pressure hydrogen pipeline explosions and (jet) fires and, to this scope, a probabilistic risk assessment procedure is proposed. The annual probability of damage to people and to buildings exposed to an extreme event is calculated as the product of the conditional probability of damage given by a fire or an explosion and the probability of occurrence of the fire/explosion as consequence of pipeline failure. The consequences of hydrogen pipeline accidents are estimated through different tools: the SLAB integral model is used to define the gas dispersion, the TNO Multi-Energy Method to evaluate the overpressure and impulse generated from the explosions and Pressure-Impulse diagrams to evaluate damage to buildings. The flame length is calculated through the SLAB model by considering the length at which the hydrogen concentrations of 4% (lower limit flammability) is reached.The point source model is employed to estimate the radiative heat flux generated by jet fire with the radiant fraction calculated through the empirical correlation proposed by Molina et al. (2007). Finally, the Probit equations are used to calculate damage to people, both in the case of an explosion and a jet fire. The characteristic quantities of the two accidental events investigated, overpressure and impulse in the case of the explosions and radiative heat flux in the case of jet fires, are considered as causative variables. Reinforced concrete buildings and tuff stone masonry buildings are taken into consideration to estimate the effect of overpressure and impulse caused by an explosion. Direct and indirect damage on the people are investigated to define the effects of consequence of explosions and jet fires. The probabilistic procedure proposed can represent a useful tool in the design of a new hydrogen distribution network and in risks assessment for existing ones.