Human error THERP

THERP Technique for Human Error Rale Prediction NUREG/CR-I278, 198.)... 

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... 

The decomposition approach is used, it is necessary to represent the way in which the various task elements and other possible failures are combined to give the failure probability of the task as a whole. Generally, the most common form of representation is the event tree (see Section 5.7). This is the basis for THERP, which will be described in the next section. Fault trees are only used when discrete human error probabilities are combined with hardware failure probabiliHes in applications such as CPQRA (see Figure 5.2). 

THERP Techniques for human error rate prediction... 

PROBLEM DEFINITION. This is achieved through plant visits and discussions with risk analysts. In the usual application of THERP, the scenarios of interest are defined by the hardware orientated risk analyst, who would specify critical tasks (such as performing emergency actions) in scenarios such as major fires or gas releases. Thus, the analysis is usually driven by the needs of the hardware assessment to consider specific human errors in predefined, potentially high-risk scenarios. This is in contrast to the qualitative error prediction methodology described in Section 5.5, where all interactions by the operator with critical systems are considered from the point of view of their risk potential. 

This approach is illustrated by the development of event trees and fault tree analysis. In fault tree analysis, the probability of an accident is estimated by considering the probabihty of human errors, component failures, and other events. This approach has been extensively applied in the field of risk analysis (Gertman and Blackman 1994). THERP (Swain and Guttman 1983) extends the conditioning approach to the evaluation of human reliability in complex systems. 

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. 

The next step employs quantitative models of human performance and technology to reach an applied decision that best satisfies the required resources if sufficient resources are available. If sufficient resources are not available, additional performance and skill resources need to be obtained to complete the task, or the task requirements need to be reduced. Quantitative models of human performance include MHP, THERP, and ERM. Using the MHP, the human processing parameters needed for each task operation are identified. The time values assigned to each parameter are used to compute task time estimates. This approach is limited to estimating performance in terms of time. THERP maps operations to the tasks included in human reliability databases to estimate human error probabflities. The ERM provides a framework for specifying performance and functional capacities at the resource level. It is the only model that (1) incorporates aU required dimensions of performance and skills and (2) uses consistent modeling constructs across tasks, humans, and machines. 

After the task is specified, human and machine performance models can be applied to estimate task performance. The MHP and keystroke-level performance model can provide task performance estimates in terms of task completion time. THERP can be used to estimate human error probabilities for each task and task sequence. The ERM approach can be used to estimate performance along any required dimension and to compare required with available resources along any required dimension as long as the human performance data are available. The results of the ERM assessment would identify stress levels on capacities (e.g., resources stressed too long or beyond maximum capacity). These results indicate limiting factors to successful task performance. Limiting factors can be identified at elemental or intermediate performance resource levels. As such, the ERM represents a more comprehensive and internally consistent model than the others. It is more comprehensive in that it can be used to model any performance dimension. It is... 

In addition, other scholars classify the human error types related to the safety production. The earliest was used in the THERP method, which divided into Commission and Omission. The... 

One method for analyzing human reUability 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 THERP, which was developed in the 1950s. As with other PRA techniques, THERP models can use either point. 

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.). 

Use of conditional human error probabihties (HEPs) to model the effect of dependence the THERP approach amounts to evaluate the probability of failure of one task, when it is known that the previous task has failed. 

The Technique of Human Error Prediction (THERP) proposes decomposition of the task considered into subtasks what has been presented on an example in Fig. 4. Human error probability is calculated taking into account combination of parameters with consideration of PSFs and dependencies between analyzed subtasks. 

The hazard identification and evaluation of a complex process by means of a diagram or model that provides a comprehensive, overall view of the process, including its principal elements and the ways in which they are interrelated. There are four principal methods of analysis failure mode and effect, fault tree, THERP, and cost-benefit analysis. Each has a number of variations, and more than one may be combined in a single analysis. See also Cost-Benefit Analysis Failure Mode and Effects Analysis (FMEA/FMECA) Fault Tree Analysis (FTA) THERP (Technique for Human Error Rate Probability). 

A technique for predicting the potential for human error in an activity. It evalnates quantitatively the contribution of the human error component in the development of an untoward system. Special emphasis is placed on the human component in prodnct degradation. THERP involves the concept of basic error rate that is relatively consistent between tasks requiring similar human performance elements in different situations. Basic error rates are assessed in terms of contributions to specific system faUutes. 

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... 

Human reliability analysis is an important component of risk analysis. Reviews of past accidents show that human error accounts for the vast majority of these events. The technique most widely used for estimating human error probabilities is called THERP (Swain and Guttman, 1983). The method uses event trees drawn in a different format to arrive at a human error probability. See Fig. 10.15 for an example. In these event trees, failure paths branch right and success paths branch left. 

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. 

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. 

There are a number of standard methods such as APJ (Absolute Probability Judgment), HEART, THERP etc to assess the potential error probability. However, these require a level of training and specialist understanding to use and those new to the assessment of human error probability should seek assistance. 

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