Risk metrics

Sielken Jr., R.L. (2000). Risk metrics and cumulative risk assessment methodology for the FQPA. Regul. Toxicol. Pharmacol., 31 300-307. 

Development of an appropriate cumulative risk metric to characterize the potential health risks of the mixture of interest. 

Selecting a model to define the POD involves several factors, most importantly the nature of the available data, the desired risk metric, and the size and statistical power of the study. Depending on whether the data is quantal (based on incidence data) or continuous (based on a continuous biological parameter), as well the nature or severity of the adverse outcome, different modeling decisions may be appropriate. For quantal data, excess risk is usually examined, while for continuous data, several other metrics may be more useful (e.g., metrics that measure relative and absolute differences in mean responses, changes in mean relative to the standard deviation of controls, changes above specified value, etc.). Using information on cancer... 

The final step in the process is to create safety risk metrics for each candidate architecture. Because the system engineers on the project created hundreds of feasible architectures, the evaluation process was automated. The actual details of the mathematical procedures used are of limited general interest and are available elsewhere [59]. Weighted averages were used to combine mitigation factors and severity factors to come up with a final Overall Residual Safety-Risk Metric. This metric was then used in the evaluation and ranking of the potential manned space exploration architectures. 

By selecting and deselecting options in the architecture description, it was also possible to perform a first-order assessment of the relative importance of each architectural option in determining the Overall Residual Safety-Risk Metric. 

This paper concentrates on the application of a Level I, at power and internal events, PRA, i.e. adopting the CDF as risk metric, to support the analysis of TS changes addressing epistemic uncertainties. 

Next, guidance is required on how to assess the impact of the uncertainties when comparing PRA results with the acceptance criteria used in decision making to delineate between acceptance and rejection with regard to the application or decision under consideration. The acceptance criteria are defined in terms of a value, or values, of risk metrics (e.g., CDF), which are given in RG 1.174 and RG 1.177. 

The importance of each causal category to the chosen risk metric in the defined case has been calculated, using the sensitivity and importance measure tools of CATS. 

ABSTRACT The Dutch government is in the process of revising its national flood safety policy. The current Dutch Flood Defense Act lays down design standards for the Dutch flood defenses. These standards have been based on/rationahzed by economic optimizations in which investment costs are balanced against the discounted value of (potential) future losses. Loss of life is not considered separately. This paper presents the results of a research project that evaluated the potential roles of two risk metrics individual and societal risk. These metrics are already used in the in the Dutch major hazards pohcy for the evaluation of risks to the public. Individual risk concerns the annual probabihty of death of an average, unprotected person. Societal risk concerns the probability of a multi-fatality event. This paper discusses technical aspects of the use of individual and societal risk metrics in flood risk management, as well as policy implications. 

The paper is organized as follows. Section two introduces the risk metrics that are used in the Dutch major hazards policy individual and societal risk. The following section discusses how these risk metrics can he quantified for flood risks. Section four then discusses alternative ways to take fatahty risks into account in a risk-informed flood safely policy. As will be shown, some uses of these risk metrics can have significant policy imphcations Case studies will illustrate how different types of interventions (e.g. dike strengthening, improving evacuation opportunities, compartmentalizing dike rings) influence individual and societal risks. The paper ends with a summary and discussion of the main results. 

RISK METRICS USED WITHIN THE DUTCH MAJOR HAZARDS POLICY... 

The second risk metric that is being considered by policymakers is individual risk. Individual risk is defined as the probability of death of an average, improtected person that is constantly present at a certain location (note that evacuation could be included in an alternative definition). As levels of individual risk are highly dependent on local flood conditions and topography, it is troublesome to estimate individual risks throughout low-lying regions, without detailed information from flood scenario calculations available. No nationwide estimates are therefore presented for individual risk. 

Because we can assume that the stakeholders polls are obtained from a finite distribution, we can measure the disagreement by using a risk metric such as CVaR. To this end we solve the following problem ... 

Lead has been shown to be carcinogenic in animals and is considered a probable carcinogen in humans. The current view of Pb carcinogenicity vis-a-vis systemic toxicity was set forth in Chapter 17. In terms of overall human health risks, carcinogenic endpoints for lead in terms of quantifiable cancer risk metrics in populations-at-large are not as reliably drawn as are noncarci-nogenic effects. Noncarcinogenic adverse endpoints are the focus for adverse health effects from Pb exposure in humans. 

The overall schematic for quantified health risk estimates in the analysis of U.S. EPA (2007) entailed combining concentration—response functions with blood lead distributional statistics generated for each of the three case studies to produce distributions of IQ loss estimates for each study population. Before the quantitative analyses of health risk were done via using differing concentration—response functions, the health risk portion in U.S. EPA s full-scale health risk assessment was evaluated to produce several statistical modeling and assessment steps for the risk metric, IQ point loss, in young children sustaining developmental neurotoxicity effects at various PbB estimates. 

RG 1.174 (USNRC, 2011) establishes two risk metrics for evaluating the risk impact of whatever change to the licensing basis (Martorell et al., 2014), which are herein adapted to address the risk impact of equipment ageing. 

Using a level 1 PSA, the required risk metrics for the evaluation of ageing are the annual average baseline CDF before ageing (named herein CDF and the change in the annual average baseline CDF due to equipment ageing, which can be formulated as follows ... 

Risk assessment is proposed by formulating the usual risk metrics for analyzing Surveillance Requirement changes in the literature, as introduced in section 2.3. It is proposed treatment of model and parameter uncertainties based on traditional sensitivity studies and uncertainty assessment respectively, the latter based of the probabilistic approach for uncertainty formulation and propagation by standard Monte Carlo Sampling (MCS) technique. 

Railway industry concerns the performance of railway system and railway assets management tries to reduce the railway accidents and the maintenance cost. Derailment is one of railway accidents leading to fatalities and a high corrective maintenance cost. On plain line, derailment may occur when a train travels along a poor condition track. Track inspections and maintenances should be carried out to maintain track condition. Traffic control such as speed restriction cooperates with track maintenance to decrease accident frequencies or reduce accident consequences. Track maintenances cost a lot of money and traffic controls always reduce line availability. System risk metrics, railway line availability and management cost are required to decide when and how to maintain the track and when to perform speed restriction to get fewer accidents with higher availability and lower cost. 

Johansen, I.L. Rausand, M. 2014 Foundations and choice of risk metrics. Safety Science 62. 62, 386-399. 

There are several sources of uncertainty linked to both the inherent capabihty of the PRA available to quantify the required risk metrics and the additional assumptions made within the PRA application to evaluate the risk impact of the particular CT change. 

Specifically concerning Technical Specifications, RG 1.177 establishes one more risk metric specific to CT changes for evaluating the risk impact associated with the revised CT, which corresponds to the single-event CT risk after the change, i.e. ICCDP , which can be derived directly using Equation 3 with the revised downtime, d, . 

The quantification of risk impact of the CT change, adopting the previous risk metrics, has to be performed in such a way that uncertainties are treated in the most appropriate way, which depends on the type of uncertainty. In this paper, special attention is paid to model and parameter uncertainties associated with human performance affected by the ECO change. 

The PRA is used to calculate the CDFj and CDFq basic risk measures, adopting 10" as the truncation limit. By using Equation 2 it is possible to quantify the conditional risk metric, ACDFj. ... 

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