Technique for Human Error Rate Prediction

S.2.9 Technique for Human Error Rate Prediction (THERP)... 

If the results of the qualitative analysis are to be used as a starting-point for quantification, they need to be represented in an appropriate form. The form of representation can be a fault tree, as shown in Figure 5.2, or an event tree (see Bellamy et al., 1986). The event tree has traditionally been used to model simple tasks at the level of individual task steps, for example in the THERP (Technique for Human Error Rate Prediction) method for human reliability... 

THERP Techniques for human error rate prediction... 

Technique for human error-rate prediction (THERP) Structure methodology for modeling human error and task completion in terms of probabilities Predicts human error and task completion probabiUties using a human performance database and expert judgments... 

The technique for human error-rate prediction (THERP) [ Swain and Guttmann, 1980] is a widely applied human reliability method (Meister, 1984] used to predict human error rates (i.e., probabilities) and the consequences of human errors. The method relies on conducting a task analysis. Estimates of the likelihood of human errors and the likelihood that errors will be undetected are assigned to tasks from available human performance databases and expert judgments. The consequences of uncorrected errors are estimated from models of the system. An event tree is used to track and assign conditional probabilities of error throughout a sequence of activities. 

For analyzing and quantifying human error nowadays mostly the Technique for Human Error Rate Prediction (THERP) procedure is applied. The method is documented in [52] along with a comprehensive data collection. Despite numerous further developments in the field it remains the procedure most suitable for practical applications. 

In current HRA practice, the most widely used dependence assessment method is the dependence model and method included in the Technique for Human Error Rate Prediction (THERP) HRA method (Swain Guttman 1983). The current practice has however a number of weaknesses. Often, the assessment is performed based on direct expert judgment so that the results lack traceability and repeatabftity. In some cases, simphfied expert elicitation approaches, hke decision trees (Gertman et al. 2004, Juluis et al. 2005) are used, which however are not based on a transparent expert ehcitation process (Podofillini et al., in prep.). 

Swain and Rook developed Technique for Human Error Rate Prediction (THERP) in 1961 to quantify human error rates due to problems of equipment unreliability, operational procedures, and any other system characteristic that could influence human behavior... 

Reason also brings to mind the antiquity of the literature on human error reduction. In his final chapter, he reviews THERP, (the technique for human error rate prediction). This methodology was developed by Alan Swain in 1963. 

There are a number of methods for evaluating the probability of human error. Two of the better-known methods are the Technique for Human Error Rate Prediction (THERP) (Reference NUREG/CR-1278) and the Accident Sequence Evaluation Program Human Reliability Analysis Procedure (Reference NUREG/CR-4772). Error rates are usually established on a per-demand basis. 

One method for analyzing human reliability is a straightforward extension of probabilistic risk assessment (PRA)—in the same way that equipment can fail, so can a human make mistakes and slips. One technique for predicting human error rates is the Technique for Human Error Rate Prediction (THERE), which was developed in the 1950s. As with other PRA techniques, THERE models can use either point. 

There have been several methods used to assess human reliability. Out of various methods, the technique for human error rate prediction (THERE) is in use since the beginning and still quite popular. Many of the HRA methods have been developed for specifically for various plants, for example, nuclear action reliability assessment (NARA). Short-working methods of important HRA methods, used as general purpose, in majority plants are shown in Fig. V/6.0-1B. 

There are a number of methods for evaluation of the probability of human error, for example, the technique for human error rate prediction, discussed earlier (Clause 6.2.1 of Chapter V). The best source for determining the human error rate would be company/facility-specific historical data, but in most organizations this is not available [11]. So, other means need to be explored. The reliability of support systems necessary for an operator s action is also an important issue that can influence risk reduction. The majority of SIS systems are designed as deenergize to actuate. The calculation of PFD for these SIS systems does not generally have to take into consideration any system outside of the SIS. See also Clause 3.2.2. 

Similarly, there many techniques to face and comhat human error such as technique for human error rate prediction (THERE), human error assessment and reduction (HEART), etc. already discussed in previous chapters. 

Various human reliability assessment techniques may be used to evaluate the effectiveness of cross-checking activities - eg THERP (Technique for Human Error Rate Prediction) and HEART (Human Error Assessment and Reduction Technique). It is important that any assessment is made by a competent human reliability specialist and that it is based on information provided by the operators who actually carry out the filling operation. 

For some time there has been an interest in exploring the underlying reasons, as well as probabilities, of human error. As a result there are currently several models, each developed by separate groups of analysts working in this field. Estimation methods are described in the UKAEA document SRDA-Rll, 1995. The better known are HEART (Human Error Assessment and Reduction Technique), THERP (Technique for Human Error Rate Prediction), and TESEO (Empirical Technique to Estimate Operator Errors). 

A THERP tree is a technique used in human reliability assessment to calculate the probability of a human error during the execution of a task. (THERP stands for Technique for Human Error Rate Prediction.) A THERP tree is basically an event tree, where the root is the initiating event and the leaves are the possible outcomes. THERP is described in a publication from 1983 (Swain, A.D. and Guttmann, H.E., Handbook of Human Reliability Analysis with Emphasis on Nuclear Power Plant Applications, NUREG/CR-1278, USNRC), and is still widely used despite its unrealistic assumptions about human performance. One important... 

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