Assessing Alternative Scenarios

While it is generally recommended to use scenario planning as a precursor to quantitative decision analysis (cf. Wright and Goodwin 1999, pp. 318-319 Geoffrion 1978, pp. 166-167), Herzhoff (2004, pp. 150-195) found in his empirical study on the use of scenario planning in chemical industry that only 43% of the participating companies actually used scenario techniques. 

The issue of scenario generation can be looked at from a content and a process perspective. The content perspective deals with the question of 

ChemNet Design Data Manage - Define demand scenarios - 

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Establish an appropriate design basis for each vessel that needs protection based on the different overpressure cases described in Section 2.3. Choosing the correct design basis requires assessing alternative scenarios to find the credible worst-case scenario. 

While assessing the contributions of alternative scenarios described above is important to understanding the mechanism of drug action, assessing the benefit or risk posed by the overall effect is a slightly different process. With respect to the first case described above, increased phytosterol absorption due to... 

The data used in this paper concern the baseline scenario and hence the results cannot he used to assess the situations related to alternative scenarios. 

In assessing the impact of in-vessel FCIs on accident progression, three alternative scenarios can be postulated ... 

Hazard assessment. A hazard assessment is required to assess the potential effects of an accidental (or intentional) release of a covered chemical/material. This RMP element generally includes performing an off-site consequence analysis (OCA) and the compilation of a five-year accident history. The OCA must include analysis of a least one worst-case scenario. It must also include one alternative release scenario for the flammables class as a whole also each covered toxic substance must have an alternative release scenario. USEPA has summarized some simplified consequence modeling... 

Another important reason for using multiple scenarios is to represent major sources of variability, or what-if scenarios to examine alternative assumptions about major uncertainties. This can be less unwieldy than including them in the model. Also, the distribution of outputs for each separate scenario will be narrower than when they are combined, which may aid interpretation and credibility. A special case of this occurs when it is desired to model the consequences of extreme or rare events or situations, for example, earthquakes. An example relevant to pesticides might be exposure of endangered species on migration. This use of multiple scenarios in ecological risk assessment has been termed scenario analysis, and is described in more detail in Ferenc and Foran (2000). 

From the standpoint of practical regulatory assessment, it would be desirable to reach a consensus on the selection of methods for routine use for pesticide risk assessments while recognizing that there may be scientific reasons for preferring alternative methods in particnlar cases. Such a consensus does not yet exist. Further case studies are required, covering a range of contrasting pesticides and scenarios, to evaluate the available methods more fully. While a consensus is lacking, it is important that reports on probabilistic assessments clearly explain how their methods work and why they were selected. 

Alternatively, with a knowledge of the reaction kinetics, it may be possible to rule out certain scenarios as being unlikely to produce the worst case. However, the reaction kinetics used to do this must be based on the reaction that actually occurs under runaway, rather than the reaction that is theoretically expected. A degree of testing of the reaction under, runaway is usually needed and, for. the information to be sufficiently reliable, this should normally have been obtained using a purpose built vent sizing calorimeter (see Annex 2). It is essential that personnel who are experienced in carrying out these tests are involved in the assessment. 

In a deterministic planning environment the most likely scenario, here scenario 2, would be considered the base case and the optimization model would be solved based on this scenario. The optimal decision would be to open facility 1 in period 1 and facility 3 in period 2 leading to a total profit of 2,590. To assess the robustness of this network to alternative demand scenarios the profit achievable with this configuration in case of the alternative demand scenarios can be assessed. In the example, for scenario 1 the overall profit would be 1,640 and for scenario 3, 2,765 respectively. Considered individually, the optimal decision for scenario 1 would be to open only facility 1 with a total profit of 1,880 and for scenario 3 to open both facilities 1 and 2 in period 1 with a total profit of 2,931. In order to explicitly incorporate the uncertainties caused by the different realization probabilities of the three demand scenarios, the optimization model can be extended into a two-stage decision with recourse ... 

If the retardation factor approach is adopted for performance assessment, the distribution coefficient should be measured under conditions that represent a worst case competition scenario. One approach to approximating conservative conditions is to pre-wash the zeolite in an effort to saturate the exchange sites with calcium, the chief competitor (e g., Cantrell, 1996). Alternatively, it may suffice to operate the columns until full breakthrough of the competing solutes is observed, as suggested by Figure 4, followed by the analysis of spatial concentrations. 

Our alternatives that suggested a more flexible attitude about the science-policy boundary seem further away from actual developments. In Europe as a translator we saw a regulatory role for Europe as a mediator between chemical regulation and debate as they were differently framed in various countries. In the last scenario, European risk consultation , expertise shifts to a European level, but provisions are made for controversy through consultation with national experts. Assessment is routinised where possible, but evaluation details are publicly available, allowing for a shift of assessment to more consultative procedures. 

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