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From the information assembled in steps 3.1 and 4.1, it is now possible to start describing accident scenarios that may occur, starting from the initiating events. This is usually a chain of events, but may also include enabling conditions and events that influence the probability that scenarios develop positively or negatively.

How far the scenarios should be developed is difficult to define precisely. In most cases, the scenarios are stopped when the immediate effects and consequences have occurred (e.g. when a collision has occurred or a fire has been extinguished). In cases where there also may be long‐term effects on assets, this may be too early.

The scenarios are important to gain a qualitative understanding of what can happen, but they are also important as a basis for quantification of the probability/frequency of the end events.

In many cases, there can be more or less endless numbers of scenarios. We therefore need to select and describe representative sets of accident scenarios. The representative set should, as far as possible, be general enough to cover all relevant accident scenarios. At the same time, the scenarios must also be specific enough to be useful for understanding how risk can be managed through adding more risk reduction measures.