Risk Assessment. Marvin Rausand
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Notes
1 1 The tolerability of risk is discussed in Chapter 5.
2 2 The main terms are defined and discussed later in this chapter.
3 3 Human errors are discussed further in Chapter 15.
Chapter 3 Main Elements of Risk Assessment
3.1 Introduction
The terms “risk analysis” and “risk assessment” are used several times in Chapters 1 and 2 without any proper definition. We define the terms as follows:
Definition 3.1 (Risk analysis)
A systematic study to identify and describe what can go wrong and what the causes, the likelihoods, and the consequences might be.
A risk analysis is, according to Definition 3.1 , aimed at providing answers to the three questions used to define risk.
Definition 3.2 (Risk assessment)
The process of planning, preparing, performing, and reporting a risk analysis, and evaluating the results against risk acceptance criteria.
In addition to planning, preparing, and reporting, risk assessment consists of two main analytical parts: risk analysis and risk evaluation, as shown in Figure 3.1 . First, a risk analysis is carried out to identify and describe relevant accident scenarios and likelihoods, which together, define the risk. The second part, risk evaluation, compares the risk determined by the risk analysis with risk acceptance criteria, as discussed in Chapter 5.
3.1.1 The Role of the Risk Analyst
The main role of the risk analyst is to answer the three questions in the definition of risk in Section 2.2.1 , and to carry out the risk analysis as correctly and accurately as possible. The analyses and the evaluations should be as objective as the available data permit, and they should be neutral, impartial, and dispassionate.
During the risk assessment process, the risk analysts have to make many judgments and interpretations that are subjective, and hence, different analysts seldom reach exactly the same answers to the three questions. Even so, the analysts should make an effort to do the job as objectively as possible.
Remark 3.1 (Terminology)
Some authors do not distinguish between a risk analysis and a risk assessment, but use the two terms as synonyms.
3.2 Risk Assessment Process
The risk assessment process consists of a sequence of steps and substeps. The steps in the process are shown in Figure 3.2 . We divide the process into six steps, and the steps are described in separate sections. The risk evaluation is very briefly described in this chapter and in general, this book does not go into a lot of detail on this process. Chapter 5 explains the principles of risk acceptance criteria, but does not go into the process of deciding whether or not the risk should be accepted because this usually involves wider considerations than just risk.
The activities are not always carried out in the same sequence as shown in Figure 3.2 . Several activities may be performed in parallel, and we may also jump backwards