8.1 Introduction

Following the occurrence of major disasters in the petrochemical industry (Piper Alpha, Bhopal, Texas City), nuclear power (Three Mile Island, Chernobyl), marine transport ( Herald of Free Enterprise, Exxon Valdez) and rail transport (Lad-broke Grove, Southall, Potters Bar) there is an increasing requirement by regulatory authorities for organisations to conduct formal safety assessments of systems. As part of these assessments, risk analysts are now required to perform evaluations of human reliability in addition to the analyses of hardware systems that are the primary focus of a typical risk assessment.

Historically, the emphasis in human reliability analysis (HRA) has been on techniques for the derivation of human error probabilities (HEPs) for use in systems analysis techniques such as fault tree analysis (see Section 8.2). However, HRA should be an integrated process that includes a systematic and rigorous qualitative analysis to identify the nature of the errors that can arise prior to any attempt at quantification. This qualitative analysis (sometimes referred to as Human Error Identification, HEI) must ensure that no significant failures are omitted from the analysis.

It is widely recognised that there are considerable uncertainties in the quantitative data available for inclusion in HRA. However, as long as the qualitative error identification process is sufficiently comprehensive, valuable insights will emerge with regard to the sources of risk, and where resources should be most cost effectively applied in minimising these risks.

In subsequent sections, an overall framework will be introduced which will integrate the qualitative...