Risk Assessment. Marvin Rausand
continuously, and it is important to know which versions of documents have been used as basis for the analysis.
3.2.2.3 Step 2.3: Familiarization
When the study team has been established, it is important that the team members have access to all relevant information and documentation so they can become familiar with the study object and its operating context. As part of the familiarization, it may be necessary to revisit the previous substep:
More information may be required because the delimitations of the study object are extended or because the information is incomplete.
Details may be insufficient and have to be supplemented.
There may be discrepancies in the documentation.
Part of the information may be unclear and open for interpretation and needs to be discussed with designers/operators.
3.2.2.4 Step 2.4: Select Method
A number of analytical methods have been developed for risk analysis. Many factors influence the choice of methods, some of which are as aforementioned:
In general, we need to choose a method that gives the answers required for the decisions to be made. This means that we need to understand the problem and the decisions to choose method.
If several alternative methods are available, we will usually choose the method that requires least work.
The acceptance criteria may determine which methods can be used. If quantitative criteria are given, quantitative methods must be used. If we do not have quantitative criteria, qualitative methods usually suffice.
Methods have been developed for special types of systems and for special types of problems. We, therefore, need to consider the system and problem type before choosing which method to apply.
If limited information about the study object is available, it may be more relevant to choose a coarse method than a detailed method. In early project phases, coarse methods are therefore often used, switching to more detailed methods later in the project.
Consider the availability of data before choosing method. If no or little quantitative input data are available, performing a quantitative analysis may not be possible.
Usually, there are time constraints on when the results need to be ready. This may place constraints on which method to choose.
The size and how complicated the study object is, will influence the choice of method.
There may be authority requirements, and/or relevant guidelines and standards that impose requirements and constraints on how the risk assessment should be performed.
An overview of the most relevant methods is given in Table 3.1 , together with an indication of the phase(s) of a system's life in which they are suitable.
Table 3.1 Applicability of analysis methods in the various phases of a system's life.
| Method (chapter) | Early design | Design | Operation | Modification |
| Checklists (10) | G | G | G | G |
| Preliminary hazard analysis (10) | G | B | M | M |
| HAZOP (10) | M | G | M | G |
| SWIFT (10) | G | M | M | G |
| FMECA (10) | B | G | M | G |
| Fault tree analysis (11) | B | G | G | G |
| Bayesian networks (11) | M | G | G | G |
| Event tree analysis (12) | B | G | G | G |
| Human reliability analysis (15) | B | G | G | G |
| Safety audits (7) | B | B | G | B |
G = good/suitable, M = medium/could be used, B = bad/not suitable.
3.2.2.5 Step 2.5: Select Data
A number of data sources are required for a risk assessment. We seldom have many alternative data sources to choose from and often we struggle to find data at all, in particular data that are directly relevant. Types of data and data sources are discussed in Chapter 9. Factors, such as quality, age, completeness, and relevance of data should be considered when making the choice.
3.2.2.6 Step 2.6: Identify Relevant Assets
Before starting the risk analysis, we need to identify the assets that are relevant to consider. The assets to consider (e.g. people, environment, and reputation) are defined as part of the scope of the study, but we may need to define more precisely which assets may be harmed by accidents. An example may be that we have to specify whether we are looking only at employees at a plant or also neighbors who may be affected.
3.2.3 Step 3: Identify Hazards and Initiating Events
The structure of step 3 is shown in Figure 3.6 .
3.2.3.1 Step 3.1: Identify and List Generic Hazards and Events
Methods that may be used to perform this step are presented in Chapter 10. The aim of this step is to answer the question “What can go wrong?” Based on the terminology discussion in Chapter 2, we see that this question may be answered in different ways. We may identify:
Sources of possible harm (i.e. hazards).
Starting