Page 547 - Marine Structural Design

Chapter 29 Risk Assessment Methodology 523

According to the purpose and the level of detail for the risk analysis, the acceptance criteria
may be:
. High level criteria for quantitative studies,
Risk matrices and the ALARP principle,
Risk comparison criteria.
Fischhoff et a1 (1981) identified and characterized various methods for the selection of risk
acceptance criteria. They indicated that values, beliefs and other factors all influence the
selection of risk acceptance criteria. The complexity of defining risk acceptance criteria
should be explicitly recognized, due to uncertainty about their definition, lack of relevant
facts, conflicting social values, and disagreements between technical experts and the public.
The selection of risk acceptance criteria is subject to a rigorous critique in terms of
philosophical presuppositions, technical feasibility, political acceptability, and the validity of
underlying assumptions about human factors.
29.3.2 Risk Matrices

The arrangement of accident frequency and the corresponding consequences in a matrix (see
Figure 29.3) may be a suitable expression of risk where many accidental events are involved
or where single value calculations are difficult. The matrix is separated into three regions as
follows:
Unacceptable risk.
Acceptable risk.
A region between acceptable and unacceptable risk, where evaluations have to be carried
out in order to determine whether further risk reduction is required or whether more
detailed studies should be conducted.

t

H
Increasing Need Further Evaluatior
fiequency

Acceptable risk

+

Increasing consequence
Figure 29.3 Risk Matrix