Skip to content

Quantified human reliability analysis (QHRA)

Major accidents in the energy and kindred process industries have illustrated the influence of people upon the performance of safety (and environmental) critical systems. Consequently, there is an increasing requirement for major accident hazard installations to demonstrate that human factors is being properly managed.

Many of the risk assessment techniques used in industry involve quantification, and the value of their outputs relies heavily on the quality of the data they used. Whilst there are some human reliability analysis (HRA) techniques and human error probability (HEP) data available to support the integration of human factors issues in these analyses, their application can be difficult. In particular, HEPs are often used without sufficient justification. 

HRA techniques are designed to support the assessment and minimisation of risks associated with human failures. They have both qualitative (e.g. task analysis, failure identification) and quantitative (e.g. human error estimation) components.

EI Guidance on quantified human reliability analysis (QHRA) focuses primarily on techniques that provide support for quantification. It aims to reduce the instances of poorly conceived or executed analyses by equipping organisations that plan to undertake, or commission, HRAs with an overview of important practical considerations. It proceeds the real value of an HRA coming not from the generated HEP, but from the in-depth understanding of task issues that results from analysis.

This publication is intended for three main audiences:

1. Plant managers or general engineering managers, responsible for commissioning HRA studies

2. Risk analysis practitioners who need to undertake HRA studies on behalf of their clients and who wish to refresh their knowledge.

3. Senior managers looking for a concise overview of the main issues associated with HRAs.

For example, a particular use of this publication is to assist those needing to quantify human reliability in safety integrity level (SIL) determination studies.

EI Guidance on quantified human reliability analysis (QHRA) builds on the qualitative approach to task analysis set out in Guidance on human factors safety critical task analysis, which purposefully excludes from quantification from its scope.

How to access this publication 

Guidance on quantified human reliability analysis (QHRA), ISBN 978 0 85293 635 1, 1st edition (November 2012) is available as a free PDF download to those that register on the EI Publications Online website, or priced hard-copy publication.

This publication was launched by an article in the November 2012 edition of Petroleum Review: Quantifying human reliability in risk assessments.