ABSTRACT

The simple model for the estimation of the probability of operator error is that HEP is assumed to be the product of five multipliers Kl to K5 (with significance as indicated above) so that:

HEP =K1 x K 2 x K 3 x K 4 x K 5

For example, in a typical process unit, based on the information available assume the following values can be applied to the five multipliers:

Therefore, HEP = (0.01)(0.5)(1)(1)(1) = 0.005 and Human Reliability, expressed as being equal to (1 -HEP) = 0.995. While having the advantage of being simple, it may not cover more sophisticated situations. The failure may be more complex because it involves not only human error, but other failures or problems. In such cases even the better human reliability assessment tools may not be totally applicable. The better route, in obtaining a quantitative result may be to apply Fault Tree Analysis (FTA) or Event Tree Analysis (ETA) and include best data available for specific tasks for human error failure rates.