Deterministic methods, risk assessment

Risk Assessment Systems. Most of the techniques, design methods and applications in this book are deterministic. That is, some worst-case accident is assumed to happen, its effects are calculated to the best of our ability, and systems or structures are then designed to contain, suppress or mitigate the explosion accident effect. 

The determination of the estimated levels of exposure is obviously a critical component of the risk assessment process. Both pesticide residue levels and food consumption estimates must be considered. Methods for determining exposure are frequently classified as deterministic and probabilistic methods (Winter, 2003). 

The environmental concentration of a stressor, either measured or estimated, is compared with an effect concentration such as an LC50 (lethal concentration to kill 50% of individuals in a theoretical population in a set period of time) or no observed effect concentration (NOEC) [31, 32]. These are simple ratios of single exposure and effects values and may be used to express hazard or relative safety. This deterministic method uses point estimates to represent one or more factors in a risk assessment and treats them as if they were fixed and precisely known [33]. The calculation of HQs... 

In classifying waste, deterministic responses generally should be of concern only for hazardous chemicals (see Section 3.2.2.1). Therefore, the only important issue for risk assessment is the most appropriate approach to estimating thresholds for induction of responses in humans. The primary concern here is that consistent approaches should be used for all substances that induce deterministic effects. NCRP s recommendation that nominal thresholds in humans should be estimated using the benchmark dose method and a safety factor of 10 or 100, depending on whether the data were obtained in a study in humans or animals (see Section 6.1.2.1), is intended to provide consistency in estimating thresholds for all substances that cause deterministic effects. 

Given the tiered system, evidently, any step in the exposure and effects assessment can be considered in a deterministic or probabilistic way. This does affect the outcomes of the risk assessment, but it does not influence the choice of extrapolation methods as guided by the decision tree itself. 

Residential exposure should be estimated by taking into account distributions of exposure factors. Methods to assess distributions are through the deterministic or probabilistic approach (Figure 6.6). The former is often taken in preventive risk assessment in which each default value is determined from each distribution as a reasonable worst-case . The estimated exposures for the deterministic approach are expected to occur in the upper range. For actual risk assessments, the probabilistic approach directly uses the parameter distributions instead of single values to calculate distributions of exposure. To characterize exposure, an... 

Also useful have been probabilistic tools in obtaining more realistic results. Probabilistic risk assessment may appear less precise as opposed to the current approach, which involves deterministic methods in the calculation of at least some values. However, the practice for the assessor is to set up a scenario and evaluate it using a number of assumptions. Thus typically the experimenter must use good judgment in considering the likeliness of certain events occur-ing, and to evaluate the probability of these events. The probability of certain situations, pathways, or scenarios has always been at the basis of the evaluation. What is new, now, is the availability of some computerized tools to measure probability. 

USNRC s policy for implementing risk-informed regulation was expressed in the 1995 policy statement on the use of probabilistic risk assessment (PRA) methods in nuclear regulatory activities. The policy statement says The use of PRA technology should be increased in all regulatory matters to the extent supported by the state-of-the-art in PRA methods and data and in a manner that complements the NRC s deterministic approach and supports the NRC s traditional defence-in-depth philosophy. 

SESSION II Risk Theory and Risk Analysis for Landslides. [1] Landslide Risk Management concepts and framework and examples (2.5 h) [2] Deterministic and Probabilistic models for slope stability evaluation (2 h) [3] Introduction to modelling of catastrophic landslide events (2 h) [4] Empirical models for travel distance (1.5 h) [5] Application examples of probabilistic methods and semi quantitative methods for landslide hazard zonation (2h) [6] Landslide Frequency Assessment (1.5 h) [7] Different components of vulnerability to landslides. Prevention and long term management of landslides (3.5 h) [8] Case Studies coal waste dump risk assessment, example from motorway in La Reunion Island, Aknes Rock slope in Norway (2 h) [9] Application of QRA to other geotechnical problems Internal erosion of dams, crater lake hazard (1.5 h) [10] Advanced numerical models initiation of landslides, propagation of sediments/climate change effects (3.5 h). 

Proper risk indices have therefore to be defined in order to characterize the ANM scheme performance. They also have to be estimated in a limited amount of time, as any request for a new DG unit connection must be answered in a limited amount of time. Deterministic methods (based on the N-1 criterion) used for network calculations in system planning are however not suitable to assess these indices, as DG units display an intermittent... 

Such approaches can also be used for ecological risk assessment, which has higher levels of uncertainty in the risk estimates due to the lower amount of information on chemical exposure patterns by wildlife. Such approaches will likely not replace the deterministic methods of conducting risk assessment, but their utility lies in identifying how protective a concentration is likely to be under likely exposure conditions. Armed with this knowledge, regulatory agencies are better able to identify... 

The safety principle and safety system design are described in Sects. 6.2 and 6.3, respectively. Then, the deterministic approach to the Super LWR safety is described in Sects. 6.4-6.7 these describe safety analysis methods, selection and classification of abnormal events, the criteria for safety analyses, and the results of safety analyses. In addition, development of a transient subcharmel analysis code and its application to the flow decreasing events are described in Sect. 6.8. Based on the safety system design and the deterministic safety analyses, level-1 probabilistic safety assessment (PSA), which is also called level-1 probabilistic risk assessment (PRA), is presented. 

The most widely used method for the design of the RCSASs is deterministic, whereby SSCs are designed to comply with guiding rules. This approach is generally complemented with a probabilistic risk assessment whose objective is to verify that the plant as designed does not have any unacceptable vulnerabilities. 

The analysis plan should specify not only how the analysis will be conducted, but also how the results will be presented. Indeed, the way results will be communicated will usually influence the choice of both model structure and analysis method and is ultimately driven by the information needs of risk managers and other stakeholders and their management goals (see Figure 2.2). Careful advance planning for the communication of results is especially important for probabilistic assessments because they are more complex than deterministic assessments and less familiar to most audiences. It may be beneficial to present probabilistic and deterministic assessments together, to facilitate familiarization with the newer approaches. 

Lawson K (2005). Pipeline corrosion risk analysis—an assessment of deterministic and probabilistic methods. Anti-Corrosion Methods and Materials, vol. 52, pp. 3-10. 

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