The validation of three human reliability quantification techniques - THERP, HEART and JHEDI: part 1 - technique descriptions and validation issues.

This is the first of a set of three papers reviewing the validity of three Human Reliability Assessment (HRA) techniques used in the UK to predict human performance in high risk industries. The techniques are used to determine the risks inherent in such industries due to human error, and also the benefit in terms of risk reduction by having human operators in the system. These techniques culminate in a quantitative human error probability for each error or failure identified, predicting how often errors or failed performance will occur. The major question with such an approach is whether such probabilities are accurate. This key validation question is answered in the second paper, which reports the results of a large and independent validation experiment. Once a technique achieves some degree of predictive validity, the next question becomes whether such a technique can consistently produce valid and accurate results. This is called the reliability of the technique, and is dependent upon its consistency of usage by different assessors. Consistency can only be analysed by investigating the detailed usage of the techniques, and such an analysis is reported in the third paper in this series. The advantage of such an analysis is that it can also lead to specification of practical guidance for practitioners, and may lead to derivation of ways to improve the reliability and consistency of usage of specific HRA techniques. This first paper introduces the three techniques themselves, and reviews the major validation criteria and issues which should be considered when trying to determine if such techniques work.