3.1 Introduction
The ultimate task for the engineer is to establish a consistent decision basis for the planning,
design, manufacturing construction, operation and management of engineering facilities such
that the overall life cycle benefit of the facilities are maximized and such that the given
requirements to the safety of personnel and environment specified by legislation or society are
fulfilled.
As the available information (regarding, e.g. soil properties, loading, material properties,
future operational conditions and deterioration processes in general) is incomplete or
uncertain, the decision problem is a decision problem subject to uncertain information.
The present chapter introduces some fundamental issues of decision making subject to
uncertain information. The presentation in turn considers general aspects of decision theory
and illustrates these using a simple example. Finally the risk analysis decision problem is
defined in general terms within the context of decision theory.
3.2 The Decision / Event Tree
In practical decision problems such as feasibility studies, reassessment of existing structures
or decommissioning of facilities that have become obsolete, the number of alternative actions
can be extremely large and a framework for the systematic analysis of the corresponding
consequences is therefore expedient.
A decision/event tree as illustrated in Figure 3.1 may conveniently represent the decision
problems.
Figure 3.1: Decision/event tree.
For the purpose of illustration the decision/event tree in Figure 3.1 considers the following
very simple decision problem. In the specifications for the construction of a production
facility, using large amounts of fresh water in the production, it is specified that a water
source capable of producing at least 100 units of water per day must be available. As it is
known that the underground at the location of the planned production facility actually
contains a water reservoir, one option is to develop a well locally at the site of the production