Importance measurement of performance shaping factors using dynamic reliability indices

The component dynamic reliability index (CDRI) for the multi-state system is transplanted to human reliability domain, and used to evaluate the importance of performance shaping factors (PSF). The concepts about PSFs and CDRI are overviewed firstly. The importance of some PSF, namely, CDRI is the probability of human error probability (HEP) changing from one level to another level caused by the PSF´s state shifting. In basic version of CREAM, HEP is predefined as four intervals. So the CDRI is the probability of HEP increasing from lower interval to upper interval caused by the degradation of common performance conditions (CPCs). It is concluded that 3-level CPC has higher CDRI than 2-level CPC does. In SPAR-H, the continuous HEP is classified as high value, medium value and low value intervals first of all. The CDRI of some PSF is the probability of HEP decreasing from high value to medium or low value because of the improvement of the PSF state. It is found that the PSFs, such as Available time, Fitness for duty, Ergonomics/HMI and Procedures with much higher or smaller multiplier may have greater CDRI. The more importance one PSF is, the more emphasis should be given. With the help of the conclusion, the risk caused by human error in nuclear power plant, space task or other risk-critical domains can be reduced more effectively.