Consequence likelihood

For those issues or transportation scenarios requiring more detail and insight than a qualitative approach offers, the next level of analysis is a semi-quantitative evaluation. A semi-quantitative risk analysis includes some degree of quantification of consequence, likelihood, and/or risk level. Once evaluated, through the combination of consequence and likelihood, a risk-based decision can be made from the analysis or additional refinement in consequence or likelihood may be necessary. This refinement of the risk analysis may rely on additional information included as part of a semi-quantitative analysis or, as warranted, on some minimal level of quantitative techitiques described in the next chapter. 

A qualitative analysis may result in an escalation of specific issues that require a more detailed analysis before appropriate decisions can be made regarding the level of risk and suitability of potential risk mitigation options. The next level of risk analysis is semi-quantitative. Semi-quantitative analyses differ from qualitative analyses in that some degree of quantification is conducted to refine the estimates of consequence, likelihood, or level of risk. 

The 4-by-4 risk matrix for this facilitated analysis is illustrated in Figure 4.5. The consequence, likelihood, and evaluation criteria definitions are detailed in Tables 4.9-4.11, respectively. 

Chemical Security Concern Location Consequence Likelihood Risk Level... 

Therefore, risk reduction options that have the potential to influence the consequence, likelihood, or both should be considered. Table 7.2 lists some commonly applied risk reduction options for consequence reduction. In addition to consequence risk reduction options. Table 7.3 lists commonly applied options for likelihood reduction. As can be seen, there is some overlap between these tables because some risk reduction options may impact both the consequence and the likelihood. These lists are not exhaustive, but provide an example of several preshipment options, as well as additional considerations when evaluating these types of risk reduction measures. 

Qualitative Risk Analysis Based primarily on description and comparison nsing historical experience and engineering jndgment, with httle quantification of the hazards, consequences, likelihood, or level of risk. 

As part of the SIL selection, more than one safety instrumented function may have to be defined because there are different hazardous events associated with the loss of level. One SIP can be associated with the loss of the pump and another SIF can be associated with the effects on downstream equipment. Since the consequences, likelihood, and safeguards are different for the various hazardous events, the SIL determined can be different for each SIF. The SRS for each SIF must clearly state the hazardous event being mitigated or prevented by each individual SIF. 

Magnitude of hazardous consequence Likelihood of the hazards being realised ... 

The likelihood of each consequence (e.g. casualties, economic losses, interruption of occupancy) related to a given failure mechanism can be evaluated using Eq. 3.1. However, a specific consequence C, may be triggered by a number of different failiue modes (i.e. Fj, F2,. .. F y). In such cases, the consequence likelihood associated with each mechanism may be evaluated separately using Eq. 3.1 and the results can be combined as follows ... 

Basically, risk analysis means analysis of consequences, likelihood, and human factors. Control measure is also a part of risk analysis, but will be dealt separately in Clause 4-4. Also in this clause three different kinds of risk analyses shown in Fig. II/4-2.3-1 will be covered. 

Assess the consequence, likelihood, and risk of each of the identified hazards using a risk matrix system such as that described in Chapter 1. 

Which scenarios that are most inqxrrtant to attend to (most critical), may, for example, be shown in a consequence-likelihood matrix as in Fig. 2.5. The consequence-likelihood matrix shows the likelihood and consequence ranking of the accidental... 

Likelihood A consequence that is certain to follow a behavior influences that behavior more powerfully than an uncertain consequence. Likelihood is scored as Certain or Uncertain, C or U. 

Quantitative risk analysis is a forecast concerning the degree of belief associated with the occurrence of future events. It normally focuses on those classes of events that are rarely expected to occur at a facility. However, because the potential consequences of such events may be so great, the possibility that the events could occur at all gives rise to concern. When a QRA generates results that reflect a very small likelihood of an event and confirm the suspicion that the event could have a severe impact, these questions inevitably arise What does it all mean What should I do about it ... 

Combining the estimated consequences and likelihood of all incident outcomes from all selected incidents to provide a measure of risk... 

Risk is often defined as the likelihood of a certain event times a measure of the severity of its consequences. Most risk assessment studies concentrate on estimating the likelihood of certain events. They often concern the release of chemicals, or accidents in engineering projects and the project outcome. In thi.s section, the subject of accidents is not covered. Risk assessment (RA), as a technique, has been adopted by various national governments, by EU, and by OECD.-... 

From a reliability engineering perspective, error can be defined by analogy with hardware reliability as "The likelihood that the human fails to provide a required system function when called upon to provide that fimction, within a required time period" (Meister, 1966). This definition does not contain any references to why the error occurred, but instead focuses on the consequences of the error for the system (loss or unavailability of a required function). The disadvantage of such a definition is that it fails to consider the wide range of other actions that the human might make, which may have other safety implications for the system, as well as not achieving the required function. 

The sociotechnical systems perspective is essentially top-down, in that it addresses the question of how the implications of management policies at all levels in the organization will affect the likelihood of errors with significant consequences. The sociotechnical systems perspective is therefore concerned with the implications of management and policy on system safety, quality, and productivity. 

From the traditional HF/E perspective, error is seen as a consequence of a mismatch between the demands of a task and the physical and mental capabilities of an individual or an operating team. An extended version of this perspective was described in Chapter 1, Section 1.7. The basic approach of HF/E is to reduce the likelihood of error by the application of design principles and standards to match human capabilities and task demands. These encompass the physical environment (e.g., heat, lighting, vibration), and the design of the workplace together with display and control elements of the human-machine interface. Examples of the approach are given in Wilson and Corlett (1990) and Salvendy (1987). 

The main thrust of the HF/E approach is to provide the conditions that will optimize human performance and implicitly minimize human error. However, there is rarely any attempt to predict the nature and likelihood of specific human errors and their consequences. By contrast, the study of human error in the context of systems reliability is concerned almost exclusively with these latter issues. It is appropriate to introduce the systems reliability assessment approach to human error at this stage because, until recently, it was largely... 

When performing human reliability assessment in CPQRA, a qualitative analysis to specify the various ways in which human error can occur in the situation of interest is necessary as the first stage of the procedure. A comprehensive and systematic method is essential for this. If, for example, an error with critical consequences for the system is not identified, then the analysis may produce a spurious impression that the level of risk is acceptably low. Errors with less serious consequences, but with greater likelihood of occurrence, may also not be considered if the modeling approach is inadequate. In the usual approach to human reliability assessment, there is little assistance for the analyst with regard to searching for potential errors. Often, only omissions of actions in proceduralized task steps are considered. 

The SRK model can also be used as part of a approach for the elimination of errors that have serious consequences proactive for the plant. Once specific errors have been identified, based on the SRK model, interventions such as improved procedures, training or equipment design can be implemented to reduce their likelihood of occurrence to acceptable levels. This strategy will be discussed in more detail in Chapter 4. 

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