Acceptability parameters for industrial risk with respect to natural-technological interactions

When industrial risks are of concern, local operators, safety management and public authorities are generally focused on technological risk sources, management deficiencies or human errors, but are often unaware of possible accidental scenarios which may derive from the impact of disastrous natural events as earthquakes, flooding or lightning on industrial establishments (Na-Tech hazard). This issue has been recently recognized by the European Community, which has financed a large-scale integrated project within the Seventh Framework Program, concerning the early recognition, monitoring and integrated management of risks related to emerging and new technologies (iNTeg-Risk). In the project, a specific task has been devoted to assess the contributions of Na-Tech risks to the overall industrial risk at community level, aiming at the improvement of the resilience of industrial facilities to technological accidents triggered by natural hazards. In the following, a general procedure for the evaluation of Na-Tech risks having considered floods, lightning and earthquakes, with specific reference to large scale equipment containing hazardous substances, is presented. Preliminary results of specific methods developed for the Quantitative Risk Assessment of industrial facilities and areas exposed to Na-Tech events are discussed. These results have clarified that the contribution of natural events to the industrial risks may be important and comparable to the purely technological risks. Furthermore, they allow the definition of priorities for the prevention and mitigation of accidental scenarios in terms of safety management, early warning systems and/or technological resources. The study also focused on the acceptability criteria for industrial installations with respect to the accidental events triggered by natural events. Important differences may arise if a classical reference for the acceptability matrix (e.g. the ALARP matrix) is used. The natural event recurrence period and the probability of its intensity and the hazard of top events require very different procedures for their estimation. Historical data are essential for natural events whereas they are less significant for industrial equipment, due to the continuous development of safety system and technology. Moreover, the figure for “frequent event” in the industrial risk matrix has a correspondent “very rare” figure for natural event in the geophysical or meteorological meaning, and the external environment is generally struggling for the natural event and overloading of public emergency systems does not allow a contribution for the industrial accidental scenario mitigation. Also, combined scenario occur when natural events strike any industrial installation, and mitigation systems are often affected at the same time, whereas single, partially mitigable scenarios are generally predicted in the normal process life and industrial safety assessment. Finally, the natural event effects may contribute to the overall risks as workers may be injured directly for the same event of for the structural damage of buildings, offices and steel structures inside the installation. In this framework, the possible definition of acceptability parameters based on threshold values for the natural events, either in terms of Na-Tech accidental scenario probability of occurrence or for the relative intensity was investigated. The proposed threshold values were obtained from the threshold values of the specific equipment categories, for each natural event, that were obtained in previous studies and from the analysis of the societal risk variation as obtained from QRA analysis.