Risk Assessment: Tools, Techniques, and Their Applications

10.1 Introduction

10.1.1 Purpose

The purpose of this chapter is to provide guidance on “how to” perform a human reliability analysis (HRA). The methodology provided is not intended to be used as a cookbook. Each situation requiring an HRA is different. The references provide more detailed instructions, alternative methods, and estimations of human error probability (HEP) values (1).

10.1.2 Background

The need for a methodical approach to perform HRAs originated from the need to perform probabilistic risk assessments (PRAs) and probabilistic safety assessments (PSAs). For this document, PRA and PSA are considered interchangeable and only PRAs will be referred to. While nuclear power plants may be the first processes to come to mind when discussing PRAs and HRAs, PRAs are performed on many processes or activities. Examples are the assembly and disassembly of nuclear weapons, petroleum refinery operations, chemical processing plants, and so on.

PRAs typically focus on equipment failures. HRAs may be used to analyze the human response to an equipment failure. The PRA may also include a section that discusses the probability of human failure being the initiating event. Even if a full-scale PRA is not performed, an HRA may be beneficial. Any process or activity that involves humans is susceptible to human error. HRAs are used to quantify the probability of human errors. HRAs can also be used to identify steps or activities in the process that can be targeted for changes that could reduce ...