From such analyses measures can then be taken to reduce the likelihood of errors occurring within a system and therefore lead to an improvement in the overall levels of safety.
An Influence diagram(ID) is essentially a graphical representation of the probabilistic interdependence between Performance Shaping Factors (PSFs), factors which pose a likelihood of influencing the success or failure of the performance of a task.
For each of the identified influences quantitative values are calculated, which are then used to derive final Human Error Probability (HEP) estimates.
IDA is a decision analysis based framework which is developed through eliciting expert judgement through group workshops.
Unlike other first generation HRA, IDA explicitly considers the inter-dependency of operator and organisational PSFs.
The IDA approach was first outlined by Howard and Matheson,[1] and then developed specifically for the nuclear industry by Embrey et al. [2].
The chosen individuals include a range of experts - typically those with first hand experience in the operational context under consideration – such as plant supervisors, reliability assessors, human factor specialists and designers.
The group collectively assesses and gradually develops a representation of the most significant influences which will affect the success of the situation.
The process is deemed complete when all participants reach a consensus that any misgivings about the discrepancies are resolved.
Perform sensitivity analyses If individual experts remain to be unsure of the discrepancies about the assessments which have been made, then sensitivity analysis can be used to determine the extent to which individual influence assessments affect the target event HEP.
This diagram was originally developed for use in the HRA of a scenario within the settings of a nuclear power situation.
& al, e. (1985) Appendix D: A Socio-Technical Approach to Assessing Human Reliability (STAHR) in Pressurized Thermal Shock Evaluation of the Calvert Cliffs Unit 1, Nuclear Power Plant.