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.
The PSF's which require to be considered are chosen by experts and are namely those factors which are regarded as most significant in relation to the context in question.
The technique consists of two modules: MAUD (multi-attribute utility decomposition) which scales the relative success likelihood in performing a range of tasks, given the PSFs probable to affect human performance; and SARAH (Systematic Approach to the Reliability Assessment of Humans) which calibrates these success scores with tasks with known HEP values, to provide an overall figure.
The primary human error of concern in this situation is ‘failure to close V0204 prior to decoupling filling hose’.
This technique also requires an ‘expert panel’ to carry out the HRA; the panel would be made up of for example two operators possessing approximately 10 years experience of the system, a human factors analyst and a reliability analyst who has knowledge of the system and possesses a degree of experience of operation.
For this example, it is assumed that the panel put forth 5 main PSFs for consideration, which are believed to have the greatest effect on human performance of the task: training, procedures, feedback, perceived risk and time pressure.
Considering the situation within the context of the task under assessment, the panel are asked to provide further possible human errors which may occur that have the potential of affecting performance e.g. mis-setting or ignoring an alarm.
For the 3 human errors which have been identified, the ratings decided for each are provided below: Were each of the identified human errors of equal importance, it would then be possible to obtain the summation of each row of ratings and come to the conclusion that the row with the lowest total rating- in this case it would be alarm mis-set- was the most probable to occur.
From the results of the calculations, as the SLI for ‘alarm mis-set’ is the lowest, this suggests that this is the most probable error to occur throughout the completion of the task.