Human Cognitive Reliability Correlation - HCR Methodology

HCR Methodology

The HCR methodology is broken down into a sequence of steps as given below:

  1. The first step is for the analyst to determine the situation in need of a human reliability assessment. It is then determined whether this situation is governed by rule-based, skill-based or knowledge-based decision making.
  2. From the relevant literature, the appropriate HCR mathematical model or graphical curve is then selected.
  3. The median response time to perform the task in question is thereafter determined. This is commonly done by expert judgement, operator interview or simulator experiment. In much literature, this time is referred to as T1/2 nominal.
  4. The median response time, (T1/2), requires to be amended to make it specific to the situational context. This is done by means of the PSF coefficients K1 (Operator Experience), K2 (Stress Level) and K3 (Quality of Operator/Plant Interface) given in the literature and using the following formula:
T1/2 = T1/2 nominal × (1 + K1)(1 + K2)(1 + K3)

Performance improving PSFs (e.g. worker experience, low stress) will take negative values resulting in quicker times, whilst performance inhibiting PSFs (e.g. poor interface) will increase this adjusted median time.

5. For the action being assessed, the time window (T) should then be calculated, which is the time in which the operator must take action to correctly resolve the situation.

6. To obtain the non-response probability, the time window (T) is divided by T1/2, the median time. This gives the Normalised Time Value. The probability of non-response can then be found by referring to the HCR curve selected earlier. This non-response probability may then be integrated into a fuller HRA; a complete HEP can only be reached in conjunction with other methods as non-response is not the sole source of human error.

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