Consequence Analyses

Once the source modeling is complete, the quantitative result is used in a consequence analysis to determine the impact of the release. This typically includes dispersion modeling to describe the movement of materials through the air, or a fire and explosion model to describe the consequences of a fire or explosion. Other consequence models are available to describe the spread of material through rivers and lakes, groundwater, and other media. 

Whereas no quantitative consequence analysis is required by this legislation, the process ha2ards analysis must include a quaHtative evaluation of the possible effects of failure of controls on employees. Details concerning development and implementation of programs for these subjects are available (37-39). 

FIG. 26-6 Overall logic diagram for consequence analysis of volatile hazardous suhstances. (CCFS-AlChK, 1989, p. 60.)... 

The consequence analysis step involves four activities ... 

Many sophisticated models and correlations have been developed for consequence analysis. Millions of dollars have been spent researching the effects of exposure to toxic materials on the health of animals the effects are extrapolated to predict effects on human health. A considerable empirical database exists on the effects of fires and explosions on structures and equipment. And large, sophisticated experiments are sometimes performed to validate computer algorithms for predicting the atmospheric dispersion of toxic materials. All of these resources can be used to help predict the consequences of accidents. But, you should only perform those consequence analysis steps needed to provide the information required for decision making. 

The results from the consequence analysis step are estimates of the statistically expected exposure of the target population to the hazard of interest and the safety/health effects related to that level of exposure. For example ... 

Number Exposed Above ERPG-2 FIGURE 9. Example of consequence analysis results. 

In any case, like frequency analysis, examining the uncertainties and sensitivities of the results to changes in boundary conditions and assumptions provides greater perspective. The level of effort required for a consequence analysis will be a function of the number of different accident scenarios being analyzed the number of effects the accident sequence produces and the detail with which the release, dispersion, and effects on the targets of interest is estimated. The cost of the consequence analysis can typically be 25% to 50% of the total cost of a large QRA. 

Consequence Phase 3 Develop Detailed Quantitative Estimate of the impacts of the Accident Scenarios. Sometimes an accident scenario is not understood enough to make risk-based decisions without having a more quantitative estimation of the effects. Quantitative consequence analysis will vary according to the hazards of interest (e.g., toxic, flammable, or reactive materials), specific accident scenarios (e.g., releases, runaway reactions, fires, or explosions), and consequence type of interest (e.g., onsite impacts, offsite impacts, environmental releases). The general technique is to model release rates/quantities, dispersion of released materials, fires, and explosions, and then estimate the effects of these events on employees, the public, the facility, neighboring facilities, and the environment. 

The Rohm and Haas Major Accident Prevention Program (Ren-shaw, 1990 Berger and Lantzy, 1996 Hendershot, 1991a) is based on potential accident consequence analysis and uses checklists based on inherently safer design principles to identify ways to eliminate or reduce hazards. 

Consequence Analysis the effects of the in the plant on the workers and the dispersed hazardous materials on the publie and environment is assessed using computer models,... 

This section reflects on the limitations of the PSA process and draws extensively from NUREG-1050. These subjects are discussed as plant modeling and evaluation, data, human errors, accident processes, containment, fission product transport, consequence analysis, external events, and a perspective on the meaning of risk. 

Papazoglou, I. A. et al., 1992, On the Management of Severe Chemical Accidents DECARA A Computer code for Consequence Analysis in Chemical Installations Case Study September 14, 1998 Ammonia Plant, J. Haz. Mat. 31, pp 135-153. 

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