Deterministic assessment

The use of default assessment factors is recommended in risk assessments, when justifiable, although the scientific background for such factors in general was considered unsatisfactory. The default assessment factors suggested are summarized in Table 5.2. It is recommended to use assessment factors derived from probabilistic distributions in favor of deterministic assessment factors, see Table 5.2. 

For example, existing databases and risk assessment publications often omit statistical measnres of variability or nncertainty and sample sizes and rarely report the underlying data. These types of information are rarely used in deterministic assessments but are a fundamental reqnirement for probabilistic assessments. 

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. 

The analyses outlined above cannot be performed without fixing certain parameter values and making simplifications. This is in reality a specific characteristic of deterministic analyses. However, the assumptions and simplifications made in probabilistic analyses are generally closer to reality than in deterministic assessments. Their extent depends on the focus and degree of detail specified for the analysis. 

As a part of the (periodic) safety reviews (BMU 1996) of the German nuclear power plants, the protection against external hazards has to be re-assessed. According to the guidance on probabilistic safety reviews (BMU 2005) and following the international state-of-the-art (IAEA 2008) the deterministic assessments have to be supplemented by probabilistic analyses. But up to now, the spectrum of external... 

The acceptance criteria should be defined for the deterministic assessment and the PSA. These normally reflect the criteria nsed by the designers or operators and are consistent with the requirements of the regnlatory body. 

Dolsek, M. Fajfar, P. 2007. Effects of masonry infills on the seismic response of a four storey reinforced concrete frame — deterministic assessment. Engineering Structures, submitted. 

The purpose of the analysis is to evaluate the failure probability of a component when it is subject to a severe situation. The failure occurs when the loading L applied to the component exceed the strength S of its composing materials. L and S are estimated by a chain of complex thermal-hydraulics and mechanics calculations. In the deterministic assessment, a margin factor ME), which is equal to the ratio S L, must exceed a safety factor equal io 1.2. The deterministic rule to be complied with is thus ME >1.2. The failure probability is therefore defined as ... 

Cetin, K.O., Seed, R.B., Kiureghian, A.D., Tokimatsu, K., Hardei L.F., Kayen, R.E. and Moss, R.E.S. Standard penetration test-based probabilistic and deterministic assessment of seismic soil liquefaction potential. Journal of Geotechnical and Geo-environmental Engineering, ASCE, 130(12) 1314-... 

Cetin KO, Seed RB, Der Kiureghian A, Tokimatsu K, Harder LF Jr, Kayen RE, Moss RES (2004) Standard Penetration Test-based probabilistic and deterministic assessment of seismic soil liquefaction potential. J Geotech Geoenviron Eng 130 1314-1340... 

The third criterion evaluates whether the plant can be operated within the opierating envelope defined by the technical specifications. Both this criterion arid the fourth criterion call for a deterministic assessment of reactor safety by comparing potential plant conditions with existing safety analyses. The technical specifications provide the safety limits and limiting operational configurations. Challenging safety limits as a result of an identified issue would normally require corrective or compensatory action prior to restart. 

Sponsor Argonne National Lab, Environmental Assessment Division, Atmospheric Science Section, 9700 S. Cass Ave., Argonne, IL 60439. Developer University of Illinois, Dept, of Mechanical Engineering, 1206 W. Green, Urbana, IL 61801. Custodians D.F. Brown University of lUinois, Dept, of Mechanical Engineering, 1206 W. Green, Urbana IL 61801. Computer It runs on a 486, Pentium PC, or any workstation. The deterministic version runs (slowly) on a 386. The stochastic version of the code was originally written for a Sun Workstation. The PC version requires at least a 486, 33 MHz machine with a minimum of 10 MB of free hard disk space. Cost None ... 

In essence, the earlier components of this overall assessment process are mainly deterministic in character (albeit with some probabilistic elements), whereas the later stages are mainly probabilistic. Not all elements of the process are quantifiable (with any degree of confidence), however and the socicii-political-cultural context of any downstream decision-making process may be intensely uncertain. Such uncertainties make the process of risk communication and debate a complex and sometimes unpredictable undertaking. It is essential therefore that those elements of the risk management process that cein be objectively einalysed and evaluated (either qualitatively or quantitatively, as appropriate) are so assessed. 

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. 

In addition, very few observations are pristine and basic measurements such as angular deviation of a needle on a display, linear expansion of a fluid, voltages on an electronic device, only represent analogs of the observation to be made. These observations are themselves dependent on a model of the measurement process attached to the particular device. For instance, we may assume that the deviation of a needle on a display connected to a resistance is proportional to the number of charged particles received by the resistance. The model of the measurement is usually well constrained and the analyst should be in control of the deterministic part through calibration, working curves, assessment of non-linearity, etc. If the physics of the measurement is correctly understood, the residual deviations from the experimental calibration may be considered as random deviates. Their assessment is an integral part of the measurement protocol and the moments of these random deviations should be known to the analyst and incorporated in the model. 

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). 

Only deterministic models for cellular rhythms have been discussed so far. Do such models remain valid when the numbers of molecules involved are small, as may occur in cellular conditions Barkai and Leibler [127] stressed that in the presence of small amounts of mRNA or protein molecules, the effect of molecular noise on circadian rhythms may become significant and may compromise the emergence of coherent periodic oscillations. The way to assess the influence of molecular noise on circadian rhythms is to resort to stochastic simulations [127-129]. Stochastic simulations of the models schematized in Fig. 3A,B show that the dynamic behavior predicted by the corresponding deterministic equations remains valid as long as the maximum numbers of mRNA and protein molecules involved in the circadian clock mechanism are of the order of a few tens and hundreds, respectively [128]. In the presence of molecular noise, the trajectory in the phase space transforms into a cloud of points surrounding the deterministic limit cycle. 

Deterministic and Probabilistic Assessment Factors Suggested for Use in Human Health Risk Assessment... 

In the following text, various studies will be described, which attempt to establish a scientific rationale for the selection of the interspecies assessment factor. Based on these studies, it can be concluded that a species-specific default factor based on differences in caloric requirement (see Table 5.4) should be used for interspecies extrapolation regarding metabolic size. The remaining interspecies differences should preferentially be described probabilistically, or a deterministic default factor of 2.5 could be used for extrapolation of data from rat studies to the human situation. 

In conclusion, the assessment factor for interindividual variability should preferentially be described probabilistically. However, at present there is no database-derived distribution of the interindividual factor and thus a deterministic default factor of 10, split evenly into a sub-factor of 3.16 for both toxicokinetics and toxicodynamics, respectively, is recommended in order to account for the interindividual variability in the human population. Alternatively, the pathway-related UF approach suggested by Renwick and Lazams (1998) and further developed as reviewed by Dome et al. (2005) could be applied in case the pathway(s) of the metabolism of the chemical in humans... 

Defining the characteristics of each level of refinement of the risk assessment and identifying which levels are deterministic and which are probabilistic... 

Irrespective of the risk, assumptions and decisions will have to be made because of uncertainty. Implications of attempting to characterize all variability and uncertainty in the risk assessment need to be considered. For example, exaggerating uncertainties can obscure the scientific basis of risk management decisions, leaving the impression that the decision has been arbitrary in nature (NRC 1989). The purpose of the uncertainty factor together with the type of assessment (e.g., deterministic or probabilistic, protective or best estimate) must be clearly communicated. Uncertainty factors can be described in 3 categories ... 

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