Risk analysis definitions

Figure 2.42 shows the variability risks analysis based on the toleranees assigned to meet the 0.2 mm toleranee for the assembly. Given that an FMEA Severity Rating (S) = 5 has been determined, whieh relates to a definite return to manufaeturer , both impaet extruded eomponents are in the unaeeeptable design region, as well as the bobbin and plunger end seal as shown on the Conformability Matrix in Figure 2.43. The toleranee for the brass tube base thiekness has no risk and is an aeeeptable design.

The Center for Chemical Process Safety s projects fall into a number of general topic areas that comprise a comprehensive program. These topic areas include identification of hazards and analysis of risks, prevention and mitigation of the hazards identified, and better definition of areas affected by a release of hazardous materials. This book is the latest in the series dealing with hazard identification and risk analysis. 

A risk analysis is not an objective by itself, but is one of the elements of the design of a technically and economically efficient chemical process [1]. In fact, risk analysis reveals the process inherent weaknesses and provides means to correct them. Thus, risk analysis should not be considered as a police action, in the sense that, at the last minute, one wants to ensure that the process will work as intended. Risk analysis rather plays an important role during process design. Therefore, it is a key element in process development, especially in the definition of process control strategies to be implemented. A well-driven risk analysis not only leads to a safe process, but also to an economic process, since the process will be more reliable and give rise to less productivity loss. 

Thus, the risk analysis must be well prepared, meaning that the scope of the analysis must be clearly defined data must be available and evaluated, to define the safe process conditions and the critical limits. Then, and only then, the systematic search for process deviations from the safe conditions can be started. The identified deviations lead to the definition of scenarios, which can be assessed in terms of severity and probability of occurrence. This work can advantageously be summarized in a risk profile, enhancing the major risks that are beyond the accepted limits. For these risks, reduction measures can then be defined. The residual risk, that is, the risk remaining after implementation of the measures, can be assessed as before and documented in a residual risk profile showing the progress of the analysis and the risk improvement. These steps are reviewed in the next sections. 

A further divide between risk analysts arises between realism and constructionism, but this debate can be seen as unifying positivist and relativist approaches. Constructionism considers how social and cultural perspectives influence risk definitions and interpretations [12]. In comparison, realists exclude social and cultural phenomena in their reference of risk, but do acknowledge their existence [12]. Constructionism resembles constrained relativism and does not represent the paradigms of the unconstrained relativists. For positivists and realists, acknowledging risk perceptions provides a potential framework to incorporate the risk perceptions into their process of risk analysis because risk perceptions can be subject to scientific analysis as social phenomena. 

Kaplan S and Garrick BJ (1981) On the quantitative definition of risk. Risk Analysis 1 11-27. 

This chapter presents the basic concepts and definition of risk (Section 3.1), a protocol for conducting transportation risk assessments (Section 3.2), and a prioritization process for identifying important issues and transportation scenarios requiring a more detailed risk analysis (Section 3.3). Due to the differences in safety and security definitions and risk assessment methodologies, the focus of Chapters 3, 4, and 5 is limited to transportation safety. Security concepts, definition, and assessment methods are presented separately in Chapter 6, with this chapter providing a high-level comparison of safety and security. 

While other terms and definitions may be used in speeifie transportation regulations and for other hazardous material activities, the definitions in Table 3.1 are consistent with those found in the Guidelines for Chemical Transportation Risk Analysis (CCPS, 1995) and Guidelines for Chemical Process Quantitative Risk Analysis, Second Edition (CCPS, 2000). These definitions are further defined and developed below. 

Are data available for the defined scenarios If data are not available, or if reasonable and verifiable assumptions cannot be made that apply to the specific transportation operation, then the scenarios may need to be modified. Simple scenarios—meaning high level or broadly representative ones—are usually better for transportation risk analysis. For instance, a scenario could be defined as a large release of a flammable from a rail car in a populated area as opposed to defining the scenario in this way a flammable rail car derails, rolls down an embankment, crashes into a building at the bottom of the hill, and results in a large release in a populated area. The first scenario, with broader definition, covers the second scenario, as well as rnai r other detailed ones that may be considered. 

An important aspect concerns the definition of the user of the system. In this section, it is assumed that the decision maker has sufficient technical knowledge about the problem of decision approached, the variables and parameters involved in this analysis. Even so, it is recommended the presence of a support analyst who is able to operate the system and interpret its results. This recommendation is due to the considerable size of the risk analysis system supported by the large number of variables, of parameters and relations between them. Accordingly, the presence of an analyst should support the process of acquisition of technical data and calculation of consequences, the implementation of procedures for elicitation and analysis of results. 

Integral part of the risk analysis of a critical system is identification and assessment of hazards that significantly contribute to risk (Rausand Hoyland 2004). The hazard analysis generates data required in the next stage of analysis, which lead to description of risk scenarios, definition of safety functions, evaluation of actual risk levels and required risk reduction. Then the technical specification of safety-related functions to be realized by the system architectures considered to select most justified one. 

Integration of or into other tools, particularly systems modeling and risk analysis tools, as the tool is an object-oriented environments, where a requirement is defined as an object with its own attribute table. The attributes can be model attachments developed within other tools and exported into TRACE. They can also be a set of original requirements de fined in a document that is used as a support for the definition of the requirements modeled in TRACE. 

In this study, qualitative aspects of ATHEANA were applied for the definition of complex accident scenarios involving human actions. The purpose of identifying deviations in accident sequences through a structured process is to verify whether the procedures are still appropriate even under these conditions. The findings, for the human failure event selected from the Human Reliability Analysis (HRA) in the previously performed Probabilistic Risk Analysis (PRA), were not related to EOPs. Thus, it was found that the major contributors to failure were rather related to the human-system interface and some crew characteristics. 

Due to absence of clear definition, which limits and which conditions should be used in the risk analysis, we can obtain very different resnlts. On the other hand, the choice of limits could be manipulated in order to increase or decrease the labelled threat zone. 

In this paper, risk is defined as usual, i.e., it is a combination of the frequency F of an (undesired) event and its consequence C. This definition follows the ISO standards in risk management terminology in general (ISO 2002) as well as specifically in the Code (ISO 2005). The Code references to the management standard in all terms related to risk, i.e., risk, risk analysis, risk assessment, risk evaluation, andriskmanagement. 

The aim of project evaluation is to use the available data to provide information which will assist decision making on the future of the project. Use of sensitivity analysis and risk analysis techniques point up areas where uncertainty in the input data has greatest effect and indicates the effects of these uncertainties on the project outcome. Such evaluation does not eliminate the need for skilled judgement in the management team nor does it necessarily make the decision process any easier. However, it does ensure that a complete view of the project is available and makes clear the need for definitive company policy on risk and profitability criteria. 

Later, details of risk analysis and risk management will make use of the safety definition for risk. 

The definition of hazard earlier in this chapter lists three elements that can lead to accidents activities, conditions and circumstances. Causes of accidents often involve unsafe acts (activities) and unsafe conditions. When performing risk analysis, one may also consider circumstances surrounding a potential event. It is not uncommon for the circumstances to add to the severity of the event. For example, an automobile crashing into another vehicle may deflect into a gasoline storage tank located nearby but not directly involved in an incident. The event just happens to occur at the tank s location. 

In fact, the lack of accuracy is not due only to the differences in the predictions from the diverse correlations. Another factor influencing it is the estimation of the fraction of the overall mass of fuel that really is involved in the fireball. As happens in many cases of risk analysis, the inaccuracy arises from the definition of the problem itself. It should be taken into account that some fuel has been leaving the vessel through the safety valves from the moment in which they opened the amount released will depend on the time elapsed between this moment and that of the explosion. Furthermore, more fuel is entrained in the wake of the propelled fragments. The final resull is fhaf if is impossible to accurately establish the mass of fuel that will actually contribute to the fireball. This difficulty is found in the criteria recommended by different authors. Nazario (1988) suggests that the mass corresponding to the maximum capacity of the vessel should be used, and Pietersen and Cendejas (1985) recommend 90% of this value other authors consider that only two-thirds or three-quarters of the initial fuel mass is finally involved in the fireball. 

The method will require the essential prerequisite work of scope definition to be carried out. It will necessarily address the next three stages of risk analysis. Then, it will provide guidance on how the output of the risk assessment stage may be used to suggest options for risk management, for example by informing the placement of safety barriers. Further, the method will be appropriate to re-analysis of the improved system and may include guidance on this. 

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