Consequence and likelihood

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

Step 2—Risk Analysis the process (qualitative or quantitative) of evaluating consequence and likelihood and estimating the overall level of risk associated with the selected scenarios. 

While security is presented separately in Chapter 6, many of the risk definihons and concepts for safety and security ate similar. One difference is that security incidents ate intenhonal, rather than accidental. This difference is the basis for understanding the hazards, potenhal consequences, and likelihood of a security scenario. Table 3.3 compares the basic elements of safety and security risk analysis for the listed risk factors. The potenhal range of incidents and the resulting consequences have similarihes and differences. The incident in both cases is the... 

The hazard-, consequence-, and likelihood-based approaches are foimded on the potential issue or combination of issues. The risk-based approach discussed here is... 

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. 

Efficient use of resources Ability to compare different transportation options Ability to easily make adjustments reflecting changing company priorities Ability to easily make adjustments to reflect changing transportation regulations Applicability to a wide range of transportation scenarios Ability to accoimt for many factors that influence risk Ability to address a range of consequences and likelihoods Ability to screen out and identify those issues that may need to be escalated for further analysis Ability to provide a preliminary relative risk estimate... 

Certain factors may require some degree of weighting or quantification in a risk analysis. Table 4.5 presents factors associated with the consequences and likelihood that may need to be considered in a semi-quantitative risk analysis. 

Refinement of Consequence and Likelihood Estimates and Preliminary Mitigation Considerations... 

Using the consequence and likelihood categories, risk matrix, and risk evaluation criteria, the team reviewed three release scenarios (small, medium, and large) for the segments identified for each of the chemical movements. The result of the semi-quantitative risk estimation for this facility s hazardous material transportation operation is detailed in Table 4.12. From this results table, the following are determined ... 

Similar to the process defined for semi-quantitative risk analysis in Chapter 4, quantitative risk is a function of consequence and likelihood. Decisions are made regarding the resnlting risk level and the need for additional risk mitigation based on a comparison of the resnlts to a set of criteria. The QRA process is illustrated in Figure 5.1. The differences between a QRA and the other simpler techniques are ... 

A TSVA can be designed to analyze security risk from a wide range of threats, from vandalism to terrorism. In theory, risk is a function of the consequence and likelihood of the range of credible transportation threat scenarios. For accidental risk analyses, consequence and likelihood are evaluated directly, but in secmity analyses, likelihood is evaluated as a function of vulnerability and threat. Therefore, security risk is defined as a measure of the consequences, vulnerabilities, and threats ... 

Risk reduction recommendations from the analysis of pre-shipment options may be the result of any or all of the parameters of the risk equations. As described in Chapter 3, risk is a function of the consequence and likelihood of the specific transportation scenario(s) under evaluation ... 

An example of this process is illustrated in Figure 7.2. In this example, an operation was evaluated with a base case risk level of I, or a higher risk that required consideration of risk reduction options. Three risk mitigation options were developed and evaluated. As can be seen, one option reduced the consequence (Option 1), one option reduced the likelihood (Option 2), and one option reduced both consequence and likelihood (Option 3). Option 3 resulted in the greatest risk reduction benefit. While the options that reduce only consequence or likelihood did reduce risk (movement across or down the matrix), the resulting level of risk, as defined on the risk matrix, did not change from risk level I. Therefore, purely on a benefit basis, Option 3 provided the greatest risk reduction. 

Once the hazards associated with a process have been defined, the corresponding consequence and likelihood values can be determined. The consequence of an event usually falls into one of three categories ... 

As already discussed, risk is generally divided into three main elements hazard, consequences, and likelihood, as shown in Eq. (1.1). The risk is also ameliorated through the presence of safeguards. 

The first and most important step in any risk management program is to identify the hazards. Hazards analysis is the most important step in risk analysis because, unless hazards are identified, consequence and likelihood reduction cannot be implemented. In the context of process safety and operational integrity programs, this usually means that a Process Hazards Analysis (PHA) must be conducted. 

Further discussion to do with consequence and likelihood analysis is provided in the next chapter. 

The development of some of the risk information shown in Table 5.2, such as consequences and likelihood, is discussed in the next chapter. The table also has a Follow-Up section— the management of which is often under the control of the PSM coordinator or someone who is charged with managing the facility s overall risk program. 

The hazards analysis team spells out the hazard, consequence, and likelihood for each finding. A perennial complaint to do with hazards analysis reports is that they are too cryptic, and that insufficient background material is provided. Therefore, it is important to provide as much detail at this point— people who read and use the risk register months or even years later will not have any knowledge of the discussion that led up to the creation of the finding. 

Finally, as shown in Figure 5.10, the findings and associated information will be recorded in the risk register. (The consequences and likelihood sections of the register will be completed once a risk analysis has been carried out, as discussed in the next chapter.)... 

It is difficult to predict the true level of risk associated with each identified event because estimated values of both consequence and likelihood are usually very approximate. In particular, predictions as to what might happen are invariably colored by the personal experiences of the persons carrying out the analysis. 

For each identified hazard, a full description of its nature, consequences, and likelihood is provided. The register contains a section for follow-up, as shown in Table 11.12. 

The topics of consequence and likelihood analysis are fraught with issues that bring into question the accuracy and usefiilness of the results because so many assumptions have to be made, and because the analysts opinions (many of which are implicit) play such an important role. For example, many fires and toxic gas releases start with a leak from a piping system. Yet the size of the leak could vary from a pinhole to a partially failed gasket all the way to a complete guillotine break... 

Determine the consequence and likelihood of the hazard scenario. This evaluation should include an examination of safety, environmental, and economic losses (including the requirements associated with safety and environmental regulations). Based on an assessment of the overall risk associated with the identified hazard, decide if additional safeguards or Layers of Protection/lndependent Protection Layers (IPL) are required. The criterion for acceptable risk could be single numerical value, or it could be determined through use of a risk matrix. 

Given this information, a hazard and risk analysis is performed (Ref. 9,10, and 11) that identifies possible hazards and then establishes the consequence and likelihood of each. On some projects, consequence is determined through detailed analysis, and on others it is done by estimation. Likewise, likelihood analysis is sometimes performed by detailed analysis and sometimes by estimation. With the emergence of... 

These two causes will result in the definition of two different safety instrumented functions because the consequences and likelihood associated with the two scenarios are different. These differences are summarized in the SIF list for well 1 (Table 13-1). 

This SAR provides a description of the HCF and its operations, an assessment of the hazards and potential accidents which may occur in the fecility. The potential consequences and likelihood of these accidents are analyzed and described. Using the process and criteria described in DOE-STD-3009-94, safety-related structures, systems and components are identified, and the important safety functions of each SSC are described. Additionally, information which describes the safety management programs at SNL are described in ancillary chapters of the SAR. 

Dose consequences and likelihoods of occurrence for each of the DBAs are summarized in Table E.6-1. 

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