B. Bach, B. Božin, D. Kavšek

Before the large industrial accidents human factor was considered as very reliable and was not accepted as a possible source of errors. Today it is evident that safety is a proper combination of factors associated with people, technology and organization. Determining the cause of equipment failures is a much more enjoyable exercise than doing the same

for human errors. People are emotional: they can be angry, scared, defensive, not trustful. Because of all that the determination of causes for human errors is much more difficult. 

In many cases definition of human factors relates to operators as the source of the human errors. Such an approach restricts the search for the true root cause of an event. In reality human factor is associated with operators as well as with managers, designers, instructors, maintenance people etc. 

Operating experience and in-depth analysis with the resulting lessons learnt are all evidence of the relevance of human errors for safety. Nuclear power plant industry has estimated the risk due to human errors closing to 70%. It is therefore obvious that sophisticated techniques are needed that will focus on. 

The root cause analysis in NPP Krško is based on the following four methods: Event and Causal Factor Charting, Change Analysis, Barrier Analysis and MORT (Management Oversight and Risk Tree Analysis). 

Event and Causal Factor Charting is used for investigation of complex problems which need to be visualized in the form of a chart so as to provide a better understanding of the chronology of an event. 

Change Analysis is usually used for a particular problem with the equipment failure by using key questions: what?, when?, where?, who? and how? to find a final answer to the question WHY something happened. 

Barrier Analysis is used for procedural and administrative problems in order to establish what barriers were failed and why. 

MORT analysis is used for large and complex problem at the management level.