Severino Zanelli

An Approach to the Assessment of Domino Accidents Hazard in Quantitative Area Risk Analysis

Publisher Summary This chapter presents an approach developed for a systematic and simplified quantitative assessment of domino effects in QARA. The severity of accidents where propagation effects took place is generally named as “domino” or “knock-on” accidents. The proposed approach shows that only in a limited number of cases a full consequence and frequency assessment is necessary for domino scenarios. QARA techniques are mainly derived from quantitative methodologies for the analysis of single risk sources. Thus, the main limitation of the QARA techniques currently available is in the correct analysis of the effects of the interaction of the different risk sources present in a narrow area. If synergetic effects are neglected, knock-on scenarios resulting from the interaction of different “top events” may be evaluated from probabilistic techniques using the maps of the physical effects (radiation, overpressure, and toxic concentration) obtained for the single events. The “Seveso-II” Directive requires assessing “domino” accident hazards inside and outside the industrial sites that fall under the obligations of the Directive.

The Estimation of Vulnerability in Domino Accidental Events

The present study was aimed to the assessment of vulnerability (death probability) of domino accidents in the framework of quantitative area risk analysis. Different approaches for the calculation of vulnerability were compared and applied for the analysis of case studies. The effects of different assumptions on the severity and risk indexes were compared.

The use of HazOp and Fault Tree techniques for the assessment of non-accident induced release frequencies in the transport of hazardous substances

No well defined methodology is present in the literature for the quantitative risk assessment of non-accident induced releases during the road or rail transport of hazardous substances. The present study was dedicated to the development of a specific technique for the estimation of release frequencies of non-accident induced releases in marshalling yards. The methodology was based on the application of Hazop and Fault Tree techniques to reference schemes for tank-car vessels transporting liquids and liquefied gases. Failure frequencies and uncertainty intervals were thus estimated. The availability of release frequencies made possible the quantitative assessment of the risk caused by this kind of releases. An italian marshalling yards was analyzed. The Aripar-GIS software was used to estimate individual and societal risk caused by the different risk sources. The results pointed out that non-accident induced releases may give a relevant contribution to global risk indexes, in particular if the transport of toxic substances is concerned.

Analysis of an accident at a solvent recovery plant

An accident in a plant for solvent recovery from solvent-contaminated wastes was examined. An experimental investigation of the accident was carried out using calorimetric and thermogravimetric techniques. The immediate cause of the accident was an unforeseen exothermic decomposition reaction. The main underlying cause of the accident was the absence of safety culture in the plant management, that resulted in the lack of a testing procedure to evaluate the thermal stability of the process feed. A simplified screening procedure based on differential scanning calorimetry was used in order to test the thermal stability of the nonvolatile fraction of the solvent-contaminated wastes present on the plant in order to be processed. More than 75% of the samples examined showed exothermal decomposition phenomena starting at temperatures higher than 100 degrees C. These phenomena were common to solvent wastes that originated from a number of different industrial activities. Thus, the thermal instability of the process feed is one of the main problems in solvent recovery operations. Our analysis of the accident suggested that the safe operation of waste solvent recovery processes requires an accurate characterization of the thermal stability of the process feed. Process safety is also increased by an adequate emergency vent and an accurate control of operating temperature, that may be reduced operating under vacuum. Safety devices may also include a water supply for emergency quench.

Quantitative Area Risk Analysis: Available Tools and Open Problems

Directive 96/82/EC (better known as “Seveso-II” Directive) on the control of major hazards caused by dangerous substances leads to relevant innovations in the safety requirements of process plants, that have a relevant impact on risk management. Among these are the inclusion of substances likely to be formed in the loss of control of chemical processes in site inventory, the evaluation of domino accident hazard, and the requirement of land-use planning criteria. The development of land-use planning (LUP) criteria for the minimisation of the industrial risk to which the population is exposed calls for the application of quantitative area risk analysis (QARA) techniques. However, the QARA techniques currently available are mainly based on the modification of risk analysis techniques originally developed for the major accident risk assessment of single risk sources. Thus, these techniques show important limitations, mainly in the assessment of the effects on the global industrial risk due to the contemporary presence of different risk sources in a narrow area. Therefore, the application of QARA techniques to land use planning in the framework of “Seveso-II” Directive requires the further development of procedures to assess specific problems as the presence of linear risk sources due to the transport of hazardous substances, the release of substances formed in the loss of control of chemical processes, domino accident hazards. This contribution addresses two of the open technological problems that arise in the application of QARA techniques to LUP. The methodologies available and the research needs in the quantitative assessment of domino hazards and of the hazards deriving from the release of dangerous substances formed in the loss of control of chemical processes are discussed. The potential impact on LUP of these hazards is also evidenced, discussing the results of two Italian case studies.