A Procedure for the Probabilistic Seismic Risk Assessment of Ng Distribution Networks

Lifelines are essential infrastructures for human activities and the economic development of a region. Lifelines vulnerability reduction is an actual question, particularly with reference to NaTech events, like earthquakes. In this regard, worldwide past seismic experiences revealed heavy damages to NG distribution networks. The gas distribution network is a critical infrastructure and its failure can cause damage to structures and injury to people. Despite the low number of accidents that occurred in the transportation of natural gas (Center for Chemical Process Safety, 1995; TNO, 1999), some serious incidents have confirmed that the transportation of hazardous materials has the potential to pose a high risk to the population. Two particularly relevant pipeline incidents occurred in 2004: the explosion of a major underground high pressure natural gas pipeline in Ghislenghien industrial park, near Ath, about 50 km (30 miles) south-west of Brussels, Belgium (HInt Dossier, 2005) and a pipeline rupture (ammonia) near Kingman, Kansas (http://www.ntsb.gov/investigations/fulltext/PAB0702.htm). The development of tools both for the risk assessment and the performance evaluation of preventive and protective measures in the transportation of hazardous materials is thus an issue of primary concern (Vianello and Maschio 2014). The safety aspects of pipelines conveying dangerous substances are not covered in specific EU regulations. It must be highlighted that the Seveso III Directive (DIRECTIVE 2012/18/EU) aims to prevent major accidents at industrial facilities, whereas transport by pipeline is not included. In fact, the same kind of accidental scenarios, in terms of frequency and severity, may occur both in fixed plants and in transportation systems. Additionally, transport accidents may occur close to, and sometimes within, densely populated areas (Fabiano et al. 2002). Natural hazards in addition can seriously affect functionality of pipelines, causing local failures. In particular in areas prone to seismic risk, buried pipelines can be subject to permanent ground motions or transitory strong ground shakings which can lead to damages and consequent release of substances. Seismic response is usually defined through fragility functions, which represent exceedance probabilities of having a series of possible damage states conditional to a specific intensity measure value. In this work, a proposal of a probabilistic framework for seismic risk assessment of buried pipelines systems located in areas prone to seismic hazard is briefly described.