A methodology for the quantitative risk assessment of major accidents triggered by seismic events

A procedure for the quantitative risk assessment of accidents triggered by seismic events in industrial facilities was developed. The starting point of the procedure was the use of available historical data to assess the expected frequencies and the severity of seismic events. Available equipment-dependant failure probability models (vulnerability or fragility curves) were used to assess the damage probability of equipment items due to a seismic event. An analytic procedure was subsequently developed to identify, evaluate the credibility and finally assess the expected consequences of all the possible scenarios that may follow the seismic events. The procedure was implemented in a GIS-based software tool in order to manage the high number of event sequences that are likely to be generated in large industrial facilities. The developed methodology requires a limited amount of additional data with respect to those used in a conventional QRA, and yields with a limited effort a preliminary quantitative assessment of the contribution of the scenarios triggered by earthquakes to the individual and societal risk indexes. The application of the methodology to several case-studies evidenced that the scenarios initiated by seismic events may have a relevant influence on industrial risk, both raising the overall expected frequency of single scenarios and causing specific severe scenarios simultaneously involving several plant units.     

The assessment of risk caused by domino effect in quantitative area risk analysis

A systematic procedure for the quantitative assessment of the risk caused by domino effect was developed. Escalation vectors, defined as the physical effects responsible of possible accident propagation, were identified for the primary scenarios usually considered in the QRA procedure. Starting from the assessment of the escalation vectors, the methodology allows the identification of credible domino scenarios and the estimation of their expected severity. A simplified technique was introduced for consequence and vulnerability assessment of domino scenarios. The overall contribution of domino effect to individual risk, societal risk and to the potential life loss index was calculated by a specific procedure, taking into account all the credible combinations of secondary events that may be triggered by each primary scenario. The development of a software package allowed the application of the procedure to several case-studies. The results evidenced the relevant modifications of the risk indexes caused by domino effect and the importance of including the quantitative analysis of domino effect in QRA, in order to correctly assess and control the risk caused by escalation scenarios.     

The quantitative assessment of domino effects caused by overpressure. Part I. Probit models

Accidents caused by domino effect are among the more severe that took place in the chemical and process industry. However, a well established and widely accepted methodology for the quantitative assessment of domino accidents contribution to industrial risk is still missing. Hence, available data on damage to process equipment caused by blast waves were revised in the framework of quantitative risk analysis, aiming at the quantitative assessment of domino effects caused by overpressure. Specific probit models were derived for several categories of process equipment and were compared to other literature approaches for the prediction of probability of damage of equipment loaded by overpressure. The results evidence the importance of using equipment-specific models for the probability of damage and equipment-specific damage threshold values, rather than general equipment correlation, which may lead to errors up to 500%.     

The assessment of the damage probability of storage tanks in domino events triggered by fire

An approach aimed to the quantitative assessment of the risk caused by escalation scenarios triggered by fire was developed. Simplified models for the estimation of the vessel time to failure (ttf) with respect to the radiation intensity on the vessel shell were obtained using a multi-level approach to the analysis of vessel wall failure under different fire conditions. Each vessel “time to failure” calculated by this approach for the specific fire scenario of concern was compared to a reference time required for effective mitigation actions and related to the escalation probability. The failure probability of each vessel was correlated to the probability of scenarios involving multiple vessel failure as a consequence of the primary fire, thus allowing a comprehensive assessment of domino scenarios triggered by fire. The application of the methodology to the analysis of several case-studies allowed the estimation of the quantitative contribution of escalation events triggered by fire to the overall individual and societal risk indexes.     

Escalation thresholds in the assessment of domino accidental events

Domino effect is responsible of several catastrophic accidents that took place in the chemical and process industry. Although the destructive potential of these accidental scenarios is widely recognized, scarce attention was paid to this subject in the scientific and technical literature. Thus, well-assessed procedures for the quantitative evaluation of risk caused by domino effect are still lacking. Moreover, a wide uncertainty is present with respect to escalation criteria, and even in the identification of the escalation sequences that should be taken into account in the analysis of domino scenarios, either in the framework of quantitative risk analysis or of land-use planning. The present study focused on the revision and on the improvement of criteria for escalation credibility, based on recent advances in the modelling of fire and explosion damage to process equipment due to different escalation vectors (heat radiation, overpressure and fragment projection). Revised threshold values were proposed, and specific escalation criteria were obtained for the primary scenarios more frequently considered in the risk assessment of industrial sites.     

Definition of a short-cut methodology for assessing earthquake-related Na-Tech risk

Na-Tech (Natural and Technological) refers to industrial accidents triggered by natural events such as storms, earthquakes, flooding, and lightning. Herein, a qualitative methodology for the initial assessment of earthquake Na-Tech risk has been developed as a screening tool to identify which situations require a much more expensive Quantitative Risk Analysis (QRA). The proposed methodology, through suitable Key Hazard Indicators (KHIs), identifies the Na-Tech risk level associated with a given situation (i.e., a process plant located in a given territory), using the Analytical Hierarchy Process as a multi-criteria decision tool for the evaluation of such KHIs. The developed methodology was validated by comparing its computational results with QRA results that involved Na-Tech events previously presented in literature.     

The analysis of domino accidents triggered by vapor cloud explosions

Domino effect is a well-known cause of severe accidents in the chemical and process industry. Several studies pointed out that the more critical step in the quantitative assessment of domino hazards is the availability of reliable models to estimate the possibility and probability of the escalation of primary accidents. This work focused on the revision of available models for the quantitative estimation of damage probability to plant equipment caused by pressure waves generated by a primary accident. Available data on damages to process equipment caused by pressure waves were analyzed. Several specific probit functions for different elements of process equipment were obtained from the analysis of failure data. The analysis of blast wave propagation in different types of explosions allowed the estimation of the expected damage probability as a function of distance from the explosion center and of explosion strength. The results obtained were used to assess safety distance criteria and to evaluate the contribution to individual risk of domino effect due to pressure waves.     

ARAMIS project: a comprehensive methodology for the identification of reference accident scenarios in process industries

In the frame of the Accidental Risk Assessment Methodology for Industries (ARAMIS) project, this paper aims at presenting the work carried out in the part of the project devoted to the definition of accident scenarios. This topic is a key-point in risk assessment and serves as basis for the whole risk quantification.

The first result of the work is the building of a methodology for the identification of major accident hazards (MIMAH), which is carried out with the development of generic fault and event trees based on a typology of equipment and substances. The term “major accidents” must be understood as the worst accidents likely to occur on the equipment, assuming that no safety systems are installed.

A second methodology, called methodology for the identification of reference accident scenarios (MIRAS) takes into account the influence of safety systems on both the frequencies and possible consequences of accidents. This methodology leads to identify more realistic accident scenarios. The reference accident scenarios are chosen with the help of a tool called “risk matrix”, crossing the frequency and the consequences of accidents.

This paper presents both methodologies and an application on an ethylene oxide storage.     

The german precursor study—methodology and insights

Probabilistic Safety Assessment (PSA) yields a systematic and quantitative prediction of possible accident scenarios at technical installations on the basis of data gained from the past experience on similar technical installations. Precursor studies are performed in order to make operational experience, as far as possible, available for support of PSAs. An Accident Sequence Precursor in a Nuclear Power Plant (NPP) is defined as an observed event scenario which could result, in coincidence with additional postulated events, in a potential severe core damage accident. In this paper, the methodology and the insights of the plant-specific German Precursor Study are explained in detail. As the results have demonstrated, the Precursor methodology is applicable for ranking of the safety significance of the observed events and for trending the plant risk level (described by the frequency of potential severe core damage accidents) versus operating time.     

The development of an inherent safety approach to the prevention of domino accidents

The severity of industrial accidents in which a domino effect takes place is well known in the chemical and process industry. The application of an inherent safety approach for the prevention of escalation events leading to domino accidents was explored in the present study. Reference primary scenarios were analyzed and escalation vectors were defined. Inherent safety distances were defined and proposed as a metric to express the intensity of the escalation vectors. Simple rules of thumb were presented for a preliminary screening of these distances. Swift reference indices for layout screening with respect to escalation hazard were also defined. Two case studies derived from existing layouts of oil refineries were selected to understand the potentialities coming from the application in the methodology. The results evidenced that the approach allows a first comparative assessment of the actual domino hazard in a layout, and the identification of critical primary units with respect to escalation events. The methodology developed also represents a useful screening tool to identify were to dedicate major efforts in the design of add-on measures, optimizing conventional passive and active measures for the prevention of severe domino accidents.     

Assessment of missile hazards: identification of reference fragmentation patterns

Industrial accidents involving fragment projection were investigated. The analysis of fracture mechanics fundamentals allowed the exploration of the relations between the fracture characteristics and the final event leading to equipment collapse. Reference fragmentation patterns were defined on the basis of the geometrical characteristics of the categories of process vessels that are more frequently involved in fragmentation accidents. Primary scenarios leading to fragment projection were correlated to specific fragmentation patterns. A database reporting a detailed analysis of more than 140 vessel fragmentation events provided the data needed to support and validate the approach. The available data also allowed the calculation of the expected probability of fragment projection following vessel fragmentation, and the probability of the alternative fragmentation patterns with respect to the different accidental scenarios, based on the observed frequencies over the available data set.     

Hazard assessment of substances produced from the accidental heating of chemical compounds

Accidental events concerning process industries can affect not only the staff working in, but also the environment and people living next to the factory. For this reason a regulation is imposed by the European Community to prevent accidents that could represent a risk for the population and the environment. In particular, Directive 96/82/CE, the so-called 'Seveso II directive', requests a risk analysis involving also the hazardous materials generated in accidental events. Therefore, it is necessary to develop simple and economic procedure to foresee the hazardous materials that can be produced in the case of major accidents, among which the accidental heating of a chemical due to a fire or a runaway reaction is one of the most frequent. The procedure proposed in this work is based on evolved gas analysis methodology that consists in coupling two instruments: a thermogravimetric analyzer or a flash pyrolyzer, that are employed to simulate accident conditions, and a FTIR spectrometer that can be used to detect the evolved gas composition. More than 40 materials have been examined in various accident scenarios and the obtained data have been statistically analyzed in order to identify meaningful correlations between the presence of a chemical group in the molecule of a chemical and the presence of a given hazardous species in the fume produced.     

荔枝包装的风险识别与分析

目的解决在荔枝包装过程中风险源难于辨识及定量分析的难题。方法提出一种基于霍尔三维因素空间和模糊故障树的风险识别与定量分析方法。构建荔枝包装的安全事件、时空结构(工位)、事故致因等3个维度的因素集,通过矩阵之间的映射关系和计算分析得到风险基本事件集合。建立荔枝包装的故障树模型,并对风险基本事件进行专家问卷评价。采用梯形模糊数及左右模糊排序法将专家的评判语言转化为风险概率值。结果经计算得到荔枝包装事故发生概率(0.0409)及风险基本事件的概率重要度。结论提出了强化标准化建设,加大技术投入等防范风险事故发生的措施。     

Risk assessment and early warning systems for industrial facilities in seismic zones

Industrial equipments and systems can suffer structural damage when hit by earthquakes, so that accidental scenarios as fire, explosion and dispersion of toxic substances can take place. As a result, overall damage to people, environment and properties increases. The present paper deals with seismic risk analysis of industrial facilities where atmospheric storage tanks (anchored or unanchored to ground), horizontal pressurised tanks, reactors and pumps are installed. Simplified procedures and methodologies based on historical database and literature data on natural-technological (Na-Tech) accidents for seismic risk assessment are discussed.Equipment-specific fragility curves have been thus derived depending on a single earthquake measure, peak ground acceleration (PGA). Fragility parameters have been then transformed to linear probit coefficients in order to obtain reliable threshold values for earthquake intensity measure, both for structural damage and loss of containment. These threshold values are of great interest when development of active and passive mitigation actions and systems, safety management, and the implementation of early warning system are concerned.The approach is general and can be implemented in any available code or procedure for risk assessment. Some results of seismic analysis of atmospheric storage tanks are also presented for validation.     

Identification of fireproofing zones in Oil&Gas facilities by a risk-based procedure

Fire is among the more dangerous accident scenarios that may affect the process and chemical industry. Beside the immediate and direct harm to workers and population, fire may also cause damages to structures, which may trigger escalation resulting in severe secondary scenarios. Fireproofing is usually applied to improve the capacity of structures to maintain their integrity during a fire. Past accidents evidenced that the available standards for fireproofing application in onshore chemical and process plants do not consider all the fire scenarios that may cause structural damage. In the present study a methodology was developed for the identification of the zones where fireproofing should be applied. The effect of both pool fires and jet fires was accounted. Simplified criteria, based on radiative heat intensity, were provided for the identification of the fire protection zones. A risk-based procedure was proposed for the selection of significant reference release scenarios to be used in the evaluation of worst credible fire consequences.     

Quantitative risk analysis of oil storage facilities in seismic areas

Quantitative risk analysis (QRA) of industrial facilities has to take into account multiple hazards threatening critical equipment. Nevertheless, engineering procedures able to evaluate quantitatively the effect of seismic action are not well established. Indeed, relevant industrial accidents may be triggered by loss of containment following ground shaking or other relevant natural hazards, either directly or through cascade effects ('domino effects'). The issue of integrating structural seismic risk into quantitative probabilistic seismic risk analysis (QpsRA) is addressed in this paper by a representative study case regarding an oil storage plant with a number of atmospheric steel tanks containing flammable substances. Empirical seismic fragility curves and probit functions, properly defined both for building-like and non building-like industrial components, have been crossed with outcomes of probabilistic seismic hazard analysis (PSHA) for a test site located in south Italy. Once the seismic failure probabilities have been quantified, consequence analysis has been performed for those events which may be triggered by the loss of containment following seismic action. Results are combined by means of a specific developed code in terms of local risk contour plots, i.e. the contour line for the probability of fatal injures at any point (x, y) in the analysed area. Finally, a comparison with QRA obtained by considering only process-related top events is reported for reference.     

Comprehensive risk assessment for rail transportation of dangerous goods: a validated platform for decision support

Currently, the most advanced and well documented risk assessments for the transportation of dangerous goods by railway take into account:

(i) statistics-based loss of containment frequencies,

(ii) specification of potential consequences for a given release situations using event tree methodology as an organisational tool and

(iii) consequence calculation models to determine a risk figure known as CCDF (Complementary Cumulative Distribution Function).

Such procedures for the risk assessment (including for example decision-making on preventive measures) may offer only a limited insight into the causes and sequences leading to an accident and do not allow for any kind of predictive analysis. The present work introduces an enhanced solution, and a related software platform, which attempts to integrate loss of containment causes and consequences with system's infrastructure and its environment. The solution features:

(i) the use of a detailed Master Logical Diagram, including fault/event tree analysis to determine a loss of containment frequency based on different initiating events, scenarios and specific basic data,

(ii) the characterization of a resulting source term following a release situation, and

(iii) the calculation of various potential impacts on the neighbouring site.

Results are wrapped into a CCDF format for each selected traffic segment. The risk-related results are integrated on a software platform, structured as a decision support system using intelligent maps and a variety of GIS (Geographical Information System) data processing procedures. The introduction of the hot spot approach, allows us to focus on the most risk-relevant areas and to use information on various railway infrastructure elements (e.g. points, tunnels), are the basis of the new models employed. The software is applicable to any railway transportation system, comprising its technical infrastructure, rolling stock, human actions, regulation and management procedures. It provides the determination of the annual societal risk due to potential accident scenarios, while also revealing information on the potential causes of an accident taking into account spatial parameters. The approach and software have been validated by a case study done for a particular traffic segment of the Swiss Federal Railway company.     

Process-oriented risk assessment methodology for manufacturing process evaluation

A process-oriented quantitative risk assessment methodology is proposed to evaluate risk associated with processes using modelling, simulation and decision-making approaches. For this purpose, risks involved in a process and the corresponding risk factors are identified through an objective-oriented risk identification approach. The identified risks are first analysed qualitatively in the failure mode effect and critical analysis process and then evaluated quantitatively in a simulation environment employing a process-based risk measurement model. To ease the decision-making process in case of multiple but heterogeneous risk measures, a global risk indicator is developed using the normalisation and aggregation techniques of the decision theory. Using the proposed methodology as a decision-making tool, alternative manufacturing scenarios (i.e. manufacturing process plans) are developed and ranked on the basis of desirability. Although the methodology is illustrated with a case study issued from the part manufacturing, it is also applicable to a wide range of other processes.     

The ARIPAR project: analysis of the major accident risks connected with industrial and transportation activities in the Ravenna area

The paper describes the ARIPAR project aimed at the assessment of the major accident risks connected with storage, process and transportation of dangerous substances in the densely populated Ravenna area in Italy, which includes a large complex of chemical and petrochemical plants and minor industries, essentially distributed around an important commercial port. Large quantities of dangerous goods are involved in various transportation forms connected with the industrial and commercial activity of the port. The project started by making a complete inventory of fixed installations and transportation activities capable of provoking major fire, explosion and toxic release events; then relevant accident scenarios were developed for the single hazard sources; probabilities were assigned to the events and consequences were evaluated; finally iso-risk contours and F-N diagrams were evaluated both for the single sources and for the overall area. This required the development of a particular methodology for analysis of area risk and of associated software packages which allowed examination of the relative importance of the different activities and typologies of materials involved. The methodological approach and the results have proved to be very useful for the priority-ranking of risk mitigating interventions and physical planning in a complex area.     

Assessment of the mineral industry NORM/TENORM disposal in hazardous landfills

The main objective of this paper is to describe the assessment methodology utilised in Brazil, to foresee the performance of industrial landfills to disposal solid wastes containing natural radionuclides arising from milling and metallurgical installations that process ores containing NORM. An integrated methodology is utilized and issues as risk, exposure pathways and the plausible scenarios in which the contaminant can migrate and reach the environment and human beings are addressed. A specific example of the procedure is described and results are presented for actual situations. The model consists of an engineered depository constructed of earthen materials which minimise costs and maintain integrity over long-term. In order to define the landfill characteristics and the potential consequences to the environment, an impact analysis is carried out, considering the engineering aspects of the waste deposit and the exposure pathways by which the contaminant can migrate and reach the environment and human beings. Analytical solutions are used in the computer program in order to obtain fast results.