Scenario review

What-If or Scenario Review or Simulations (e.g., dry-runs or table top drills) Flexible method that can handle unanticipated issues Requires competent facilitator to ensure complete and effective RA... 

Select the organizational level Identify the scope of the KPI measurement system Identify incident scenarios—what can go wrong Identify the immediate causes of hazard scenarios Review performance and nonconformances... 

Most hazard identification procedures have the capabiUty of providing information related to the scenario. This includes the safety review, what-if analysis, hazard and operabiUty studies (HAZOP), failure modes and effects analysis (FMEA), and fault tree analysis. Using these procedures is the best approach to identifying these scenarios. 

When considering release scenarios, the most hazardous unit in a plant should be chosen, based on inventoiy and process conditions. The idea is to imagine the release of material in the fastest way that is reasonably possible. The worst realistic scenario should be considered. This can be based on the outcome of a review, from a HAZOP study or a hazard analysis. The time a scenario will take is almost always considered to be continuous, because after a few minutes a stable dispersion distance exists. Making the time longer will not necessarily change the hazard distance. 

Review of planned operation of process, especially the possibility of upsets, modes of failure, unexpec ted delays, redundancy of equipment and instrumentation, critical instruments and controls, and worst-credible-case scenarios... 

After the incident, an investigation team determined that the first operator had not added the initiator when required earlier in the process. When the relief operator added the initiator, the entire monomer mass was in the reactor and the reaction was too energetic for the cooling system to handle. Errors by both operators contributed to the runaway. Both operators were performing many tasks. The initiator should have been added much earlier in the process when much smaller quantities of monomer were present. There was also no procedure to require supervision review if residual monomers were detected. The lesson learned was that operators need thorough training and need to be made aware of significant hazardous scenarios that could develop. 

Frequency Phase 3 Use Branch Point Estimates to Develop a Ere-quency Estimate for the Accident Scenarios. The analysis team may choose to assign frequency values for initiating events and probability values for the branch points of the event trees without drawing fault tree models. These estimates are based on discussions with operating personnel, review of industrial equipment failure databases, and review of human reliability studies. This allows the team to provide initial estimates of scenario frequency and avoids the effort of the detailed analysis (Frequency Phase 4). In many cases, characterizing a few dominant accident scenarios in a layer of protection analysis will provide adequate frequency information. 

Its unique design suggests several accident scenarios that could not occur at other reactors. For example, failure to supply ECC to 1/16 of the core due to the failure of an ECC inlet valve. On the other hand, some phenomena of concern to other types of reactors seem impossible (e.g., core-concrete interactions). The list of phenomena for consideration came from previous studies, comments of an external review group and from literature review. From this, came the issues selected for the accident progression event tree (APET) according to uncertainty and point estimates. 

B. D. Berkey, T. H. Pratt, and G. M. Williams, Review of Literature Related to Human Spark Scenarios, Paper presented at AlChE Loss Prevention Symposium, Minneapolis, Aug. 1987. 

Figure 1 shows part of a solvent phase polypropylene plant. The plant consists of three process lines, denoted A, B, and C. During a risk assessment review, a scenario was identified that involved a release of reactor contents from a location near the west end of the A line. Estimates are needed of the blast overpressures that would occur if the resulting cloud of vapor, mist, and power ignites. 

You can quickly identify these plant sections by reviewing process flow diagrams and valving arrangements. Isolation points are defined by control valves or powered block valves that can be remotely activated. Process hazard analysis techniques help you identify the maximum credible accident scenarios. (Note that manual valves should not be considered reliable isolation points unless they are located to be accessible following a major accident. However, remotely-activated valves can only be considered reliable isolation points if there are adequate reliability engineering and maintenance programs in place.)... 

This chapter aims to review current knowledge on the effects of wastewater treatment plant (WWTP) inputs (as major nutrient point sources) on stream nutrient dynamics, with major emphasis on nutrient loads and in-stream nutrient retention, and to discuss its implications within the context of actual and future scenarios of water scarcity conditions. Following this introduction, the second section of this chapter describes water quality problems associated with wastewater inputs from urban areas and how they are faced within the context of increasing urbanization across the world and its higher impact on water availability. In the third section, we... 

Tables (3-1, 3-2, and 3-3) and figures (3-1 and 3-2) are used to summarize health effects and illustrate graphically levels of exposure associated with those effects. These levels cover health effects observed at increasing dose concentrations and durations, differences in response by species, minimal risk levels (MRLs) to humans for noncancer end points, and EPA s estimated range associated with an upper- bound individual lifetime cancer risk of 1 in 10,000 to 1 in 10,000,000. Use the LSE tables and figures for a quick review of the health effects and to locate data for a specific exposure scenario. The LSE tables and figures should always be used in conjunction with the text. All entries in these tables and figures represent studies that provide reliable, quantitative estimates of No-Observed-Adverse-Effect Levels (NOAELs), Lowest-Observed-Adverse-Effect Levels (LOAELs), or Cancer Effect Levels (CELs).

If one is less restrained in setting specification limits, a balance can be struck between customer expectations and the risk and cost of failure a review of available data from production and validation runs will allow confidence limits to be calculated for a variety of scenarios (limits, analytical procedures, associated costs see Fig. 2.15 for an example). 

The risk assessment process begins by identifying specific accident scenarios that apply to the facility under review. Steps include ... 

Each scenario was modeled to determine the explosion overpressure at the three buildings under review. The resultant overpressures, and corresponding vulnerability estimates, for the most severe scenario in each process area are tabulated below. 

The following event scenarios of concern were identified during a thorough HAZOP review that was performed as part of this assessment ... 

The basic mechanism of dryout almost invariably involves the rupture of a residual thin liquid film, either as a microlayer underneath the bubbles or as a thin annular layer in a high-quality burnout scenario. Bankoff (1994), in his brief review of significant progress in understanding the behavior of such thin films, discussed some significant questions that still remain to be answered. 

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