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Regional Basic Professional Training Course in Korea

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11. Human Performance: A Perspective on Human Factors<br />

A variety of methods exist for Human Reliability Analysis (HRA) [Kirwan and<br />

A<strong>in</strong>sworth, 1992; Kirwan, 1994]. Two general classes of methods are those based on<br />

probabilistic risk assessment (PRA) and those based on a cognitive theory of control.<br />

11.4.1. PRA‐Based Technique<br />

One method for analyz<strong>in</strong>g human reliability is a straightforward extension of probabilistic<br />

risk assessment (PRA): <strong>in</strong> the same way that equipment can fail <strong>in</strong> a plant, so can a<br />

human operator commit errors. In both cases, an analysis (functional decomposition for<br />

equipment and task analysis for humans) would articulate a level of detail for which<br />

failure or error probabilities can be assigned. This basic idea is beh<strong>in</strong>d the Technique for<br />

Human Error Rate Prediction (THERP) [Swa<strong>in</strong> & Guttman, 1983]. THERP is <strong>in</strong>tended<br />

to generate human error probabilities that would be <strong>in</strong>corporated <strong>in</strong>to a PRA. The<br />

Accident Sequence Evaluation Program (ASEP) Human Reliability Procedure is a<br />

simplified form of THERP; an associated computational tool is Simplified Human Error<br />

Analysis Code (SHEAN) [Wilson, 1993]. More recently, the US Nuclear Regulatory<br />

Commission has published the Standardized Plant Analysis Risk (SPAR) human<br />

reliability analysis method also because of human error (SPAR‐H) [Gertman et al, 2005].<br />

A. Technique for Human Error Rate Prediction (THERP)<br />

The Technique for Human Error Rate Prediction (THERP) is a first generation<br />

methodology which means that its procedures follow the way conventional reliability<br />

analysis models a mach<strong>in</strong>e. The technique was developed <strong>in</strong> the Sandia Laboratories for<br />

the US Nuclear Regulatory Commission. Its primary author is Swa<strong>in</strong>, who developed the<br />

THERP methodology gradually over a lengthy period of time. THERP relies on a large<br />

human reliability database conta<strong>in</strong><strong>in</strong>g HEPs which is based upon both plant data and<br />

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