Risk of Vessel Accidents and Spills in the Aleutian Islands Designing a Comprehensive Risk Assessment - Special Report 293 (2009) / Chapter Skim
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2 Fundamentals of Risk Assessment
2 Fundamentals of Risk Assessment
Pages 28-56
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From page 28... ...
The process for answering these three questions is called "risk analysis," and the answers derived, for all possible scenarios, are a complete expression of the risk being assessed. This chapter provides an overview of risk assessment; describes the overall organization of and approach to risk assessment; and summarizes the committee's proposed approach for a risk assessment of shipping operations in the Aleutian Islands, which is detailed in Chapters 5 and 6.
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From page 29... ...
, use the same overall approach as FSA and generally comprise the following steps: • Hazard identification, • Risk analysis, • Risk control options, • Cost–benefit assessment, and • Recommendations for decision making. Step 1: Hazard Identification The hazard identification step, in the IMO approach, might more properly be called the hazard and accident scenario identification step.
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From page 30... ...
and associated scenarios within the scope of the risk assessment study. In the case of shipping operations, the objectives of hazard identification are to • Identify specific hazards involved in shipping that have the poten tial to harm human life and health, property, or the environment;1 • Identify accident types (e.g., drift groundings, powered groundings, collisions)
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. Step 2: Risk Analysis Once hazards and accident scenarios have been identified, detailed analysis of risks can begin.
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estimations of risk and to provide detail sufficient for examining risk reduction measures that can achieve a tolerable level of risk (NRC 1989)
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. For the present study, the committee identified preliminary consequences of concern following a series of informational meetings (see the "Risk Assessment Approach" section later in this chapter)
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Step 3: Risk Control Options The next step is to identify possible risk control measures, prioritize and identify those that are more promising, and analyze their effectiveness. The results of the screening process associated with hazard identification and the risk analysis of the existing system allow the assessment of risk control measures to focus on scenarios identified as having the highest risk, considering the combination of likelihood of occurrence and consequences.
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Documentation of the recommendations should include a description of the evaluation criteria used in ranking the risks and risk reduction measures. It should also include an explanation of significant uncertainties associated with the recommendations (NRC 1989)
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When a risk assessment is intended to aid decision makers in identifying and reducing technological risks of considerable public concern, some elements of how best to organize the study are matters of choice that are not easily prescribed. Primary among these is the relationship to be developed among managers and decision makers, analysts, those with local knowledge of the technological system undergoing analysis, others with a detailed understanding of the potential local environmental and socioeconomic impacts associated with the risks of concern, and the broader stakeholder community of interested and affected parties.
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. Problem/ Context Evaluation Risks Engage Stakeholders Actions Options Decisions FIGURE 2-4 Engagement of stakeholders in the risk assessment and management process.
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. The PWS study's steering committee was constituted to be broadly representative of the main groups with an interest in risk reduction in Prince William Sound, groups that, in the aftermath of the 1989 Exxon Valdez oil spill, had highly adversarial relationships.
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From page 39... ...
study of the potential social impacts of the M/V Selendang Ayu spill and the committee's meetings with community leaders in Dutch Harbor, the Dutch Harbor community has enjoyed considerable economic benefit from its position as home port to major Bering Sea–Gulf of Alaska fisheries that are among the most economically valuable in the world. These economic benefits have translated into substantial social and cultural benefits to the community at large, making it a place that residents value for the high quality of life it now affords (Ritchie and Gill 2006)
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From page 40... ...
. The choice was made to pursue this path because the study's steering committee insisted that only local data be used in the study, rather than the worldwide data often used to support estimates of the likelihood of rare events in risk studies.
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From page 41... ...
Yet in the PWS study, the primary source of collision risk was found to be a collision between a fishing vessel and a Trans-Alaska Pipeline System trade tanker, a risk traceable to the large number of fishing vessels present within Prince William Sound during fishing seasons. RISK ASSESSMENT APPROACH This section presents a brief exposition of the general ideas behind risk assessment to set the stage for discussion of the specific tasks required for the risk assessment of shipping operations in the Aleutian Islands.
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The number of columns and rows depends on the depth of the completed analysis and the intended use of the results. Risk scenarios analyzed are placed in the cells of the risk matrix according to their level of likelihood and consequences.
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A far better method for representation of risk is known as a "risk curve" or "risk profile." The risk curve is developed from the complete set of risk triplets. The triplets are presented in a list of scenarios rearranged in order of increasing consequences, that is, C1 ≤ C2 ≤ C3 ≤ .
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Indeed, the majority of risk assessments fall P1 Staircase function P = Probability of exceedance P2 P3 Smoothed risk curve P4 PN C1 C2 C3 C4 CN Consequences FIGURE 2-6 Risk curve. (Source: NRC 1997.)
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From page 45... ...
To characterize the risks and begin to understand how the likelihood and consequences of spills can be mitigated, it is then necessary to understand the accident scenarios, that is, the series of steps leading up to these dominant accident types. The development of accident scenarios begins with identification of the conditions that affect the progress of the scenarios and limit their consequences.
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To extract the most useful information from the historical record, a model is needed. For this purpose, the committee proposes an extension of the simplified accident scenario model illustrated in Figure 2-7.
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for Control Accident Immediate Opportunity Environmental Remediation Categories Damage for Control Consequences FIGURE 2-10 Basic scenario model for Aleutian shipping risk analysis.
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[Crew and rescuers usually have multiple opportunities to control the accident, and the analysis team must identify and model them. They are grouped into two general types in the basic scenario model: the opportunity to con trol events (a)
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From page 49... ...
• Pairs of consequences and conditions can be examined, and con ditional probability estimates can be developed, such as the likelihood of drift groundings involving bad weather or collisions occurring in passes compared with other locations. Finally, the basic scenario model provides a useful structure for evaluating and comparing risk control options.
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RISK ASSESSMENT OF ALEUTIAN SHIPPING OPERATIONS The approach for the Aleutian Islands risk assessment proposed by the committee encompasses all the steps in IMO's FSA identified earlier in Figure 2-1: hazard identification, risk analysis, risk control options, cost–benefit assessment, and recommendations for decision making. However, the organization and sequencing of the specific tasks necessary to complete these steps need to reflect lessons learned from many previous risk assessments.
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The work begins with the Phase A risk analysis, which provides a high-level estimate of the likelihood and consequences of Responsible Party Define the Problem and Risk Management Approach This committee Collaborative effort of Advisory Panel, Perform the Risk Assessment Management Team, Risk Analysis Team, and Peer Review Panel Final Report Documenting Collaborative effort of Management Team Assessment and Recommendations and Advisory Panel Decision-Making Process Decision makers Implementation of Risk Reduction Measures Monitoring FIGURE 2-12 Steps in the risk management process for the Aleutian Islands.
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In Phase B, detailed analysis provides more rigorous comparisons of risk with and without specific risk control measures. The analysis includes quantitative risk analysis to estimate the effectiveness and benefit–cost of risk reduction measures, ranking of the measures, and the recommendation of measures for implementation.
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Prioritizing of Risk Reduction Measures 10. Peer Review Phase B Focused Risk Assessment: Comparative Analysis of Risk Control Options 1a.
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The analysts will have defined the full range of scenarios that may be of interest and investigated the fate of a representative set of spills in a representative set of locations along the Aleutian chain. Local experts and stakeholders will have proposed a set of risk reduction options, evaluated their feasibility and potential impacts on each element of the scenarios, and made preliminary recommendations for prioritizing the options.
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1998. Review of the Prince William Sound, Alaska, Risk Assessment Study.
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1996. Prince William Sound, Alaska, Risk Assessment Study Final Report.
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