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 points for accident scenarios (i.e. initiating events).
Events that are the “center” of the bow‐tie (i.e. hazardous events).
Events and conditions that trigger accidents (i.e. enabling events and conditions).
At an initial stage of a practical risk analysis, we often identify several or all of these when we try to answer the question. We may identify both flammable materials, gas leaks, ignition, fire, and explosion as separate hazards/events to consider, but when we inspect these more closely, we can see that they can form different events in a sequence, that is, an accident scenario.
The important point in this process is to identify as many events and conditions as possible. At this stage, we should not be too concerned about whether these are hazards, initiating events, enabling events, or enabling conditions.
Hazard and event identification may be supported by generic lists of hazards. Examples of such lists can be found in the standards related to machinery safety (ISO 12100 2010) and for major accident hazard management during design of offshore installations (ISO 17776 2016). When looking at these lists, we often find that the lists are also a mix of hazards, initiating events, and enabling events and conditions in the way that it is defined in this book. This may be confusing, but this should not stop us from using these lists for brainstorming purposes because the structuring of the information can be done afterwards.
3.2.3.2 Step 3.2: Define Specific and Representative Events
In this step, we have to be more careful about what we include as events to be analyzed further. From the (often unorganized) list of identified hazards and events, we should specify a set of specific initiating or hazardous events to form the backbone of the risk analysis. Now, the definitions introduced in Chapter 2 help us in the screening process. We should not discard any hazards and events that are not included in the list of hazardous/initiating events, because they can be parts of accident scenarios or causes that we use in later steps in the risk assessment process.
From the generic lists, we may have identified “fire” as an event, but we now need to make this sufficiently specific, stating, for example, “fire in room X during daytime.” The specificity of the events must be balanced with the resources required to perform the analysis. More events typically require more time and resources to perform the analysis so we try to define representative events that can cover a range of more or less similar events.
In most cases, a screening of the identified events may be performed as part of this step. Events that are considered to have a very low probability of occurrence or are expected to have no or negligible consequences are usually screened out and not included for further analysis. This screening should be carefully documented.
3.2.3.3 Step 3.3: Identify Causes of Events
The purpose of the causal analysis is to identify the causes of the hazardous or initiating events that have been identified. How
