The overall goal of THERP is to apply and document probabilistic methodological analyses to increase safety during a given process.
Second-generation techniques are more theoretical in their assessment and quantification of errors, addressing, rather, the schematic’s situational or interactive elements.
HRA techniques are utilized for various applications in a range of disciplines and industries including healthcare, engineering, nuclear power, transportation, and business.
The probabilities for the human reliability analysis event tree (HRAET), for example, are a calculative assessment tool drawn from a database developed by authors Alan D. Swain and H. E. Guttmann.
The resultant tree portrays a step-by-step account of the stages involved in a task, in a logical order.
The technique is known as a total methodology[2] because it simultaneously manages many different activities, including task analysis, error identification, and representation in the form of HRAET and HEP quantification.
THERP is a first-generation methodology, which means that its procedures follow the way conventional reliability analysis models a machine.
[2] THERP relies on a large human reliability database that contains HEPs and is based upon both plant data and expert judgments.
The technique was the first approach in HRA to come into broad use and is still widely used in a range of applications even beyond its original nuclear setting.
The trees’ compatibility with conventional event-tree methodology i.e. including binary decision points at the end of each node, allows it to be evaluated mathematically.
HRAETs provide the function of breaking down the primary operator tasks into finer steps, which are represented in the form of successes and failures.
The following example illustrates how the THERP methodology can be used in practice in the calculation of human error probabilities (HEPs).
In order for the final HEP calculation to be valid, the following assumptions are required to be fulfilled: The method considers various factors that may contribute to human errors and provides a systematic approach for evaluating and quantifying these probabilities.
This helps identify which factors have the most significant influence on the predicted human error rate.
THERP is widely used in industries where human performance is critical, such as nuclear power, aviation, and chemical processing.