Failure probability of reinforced concrete buildings as consequence of hydrogen pipeline explosions

In recent years, hydrogen has attracted a significant amount of public attention as an alternative source of energy replacing the traditional hydrocarbon based energies. The main diference in the delivery and supply aspects for hydrogen as a energy carrier and hydrogen as an industrial raw material lies in the fact that the former element has to deal with supplying an unspecified range of general consumers. Pipelines provide a costs efective way of distributing hydrogen in large quantities over short distances and hence they are often found serving satellite customers who take hydrogen from a local central production source (e.g. refinery or chemical plant). The failure of a high-pressure hydrogen pipeline can lead to various outcomes, some of which can pose a significant threat to people and property in the vicinity of the failure location. For a given pipeline, the type of hazard that develops and associated efects in terms of damage, injured and fatalities will depend on the mode of line failure (i.e. leak vs. rupture), the nature of gas discharge (i.e. vertical vs. inclined jet, obstructed vs. unobstructed jet) and the time to ignition (i.e. immediate vs. delayed). If a hydrogen explosion occurs, structures located close or within the ignited gas cloud are subjected to severe overpressures and may sufer loss of one or more components. After that blast overpressures vanish, local damage to some structural members may propagate throughout the structure resulting in a progressive collapse [1]. Structural safety to this type of accidents needs to account for many uncertain parameters related to loads and structural system, hence requiring a quantitative risk approach. In this paper, a probabilistic risk assessment procedure for the estimation of the failure probability of reinforced concrete columns threatened by hydrogen pipeline explosions is presented. Structural risk is estimated as convolution of blast hazard and fragility of single reinforced concrete columns. Physical features such as the gas jet release process, fammable cloud size, blast generation and propagation, and explosion efects on building columns are considered and evaluated through the SLAB integral model, TNO Multi-Energy Method [2] and structural blast fragility surfaces. Monte Carlo simulation was carried out to generate variations of reinforced concrete columns, pipelines and environmental conditions. Blast hazard was assessed considering the infuence of wind and congestion. From a structural standpoint, diferent probability distributions were used to consider uncertainty in material and geometrical properties, as well as capacity models. Assuming a threshold probability of structural collapse, a (minimum) risk- targeted safety distance between pipeline and building was derived. The threshold probability is the de minimis risk defining the acceptable risk level below which society normally does not impose any regulatory guidance. This safety distance may be used as a threshold below which existing buildings should be assessed against hydrogen pipeline explosions. The proposed methodology may be also applied to regulate the distance of new buildings from pipelines, namely for urban planning purposes. References [1] F. Parisi, N. Augenti “Infuence of seismic design criteria on blast resistance of RC framed buildings: A case study”, Engineering Structures, 44, 2012, 78-93 [2] C.J.H. van den Bosch, R.A.P.M. Weterings (Eds.) “Methods for the calculation of physical efects due to releases of hazardous materials (liquids and gases) Yellow book”, TNO, The Hague, 2005