Chapter 6 - Assessing the Frequency or Likelihood of Potential Hazardous Incidents or Losses

Abstract

This chapter analyzes the possible contributory factors that can lead to a possible plant incident. It describes the ways to estimate the probability of such incidents and recognize some of the common weaknesses in the design or operation of instrumented control and protective systems that increase the likelihood of mishap. The chapter discusses a systematic approach to the analysis of the causes as a basis for quantification of likelihood, and then explains the mathematical methods for quantifying those elements that can be quantified. It also provides some broadly indicative data to use in preliminary assessments. In hazard analysis and probabilistic risk assessment, it is dealt more with unreliability than with reliability, the frequency of failures, or with the probability that an item of equipment will not operate as required when called upon to do so. The chapter deals with the frequency of incidents that have a severe physical impact as a result of the failure. The cutset approach is an alternative approach to assess the failure frequency of a system. The chapter explains the probabilities of various outcomes that can be estimated with the aid of an event tree and covers modeling and the methods of improving reliability of control and protective system.