Inclusion of Human Factor into Risk Assessment through a Fuzzy Frequency Modifier

The frequency of an accident’s occurrence is a key aspect to take into consideration in the field of risk assessment. Aspects such as the human factor, which is a major cause of undesired events in process industries, are usually not considered explicitly in the frequency estimation, mainly due to the uncertainty and complexity associated to them. Failure frequencies are modified by a fuzzy modifier that has been developed in order to introduce the human factor in their estimation. The model includes variables such as Organizational Factors, Job Characteristics Factor and Personal Characteristics Factor. Applying this methodology, new values of frequencies have been obtained. To develop the fuzzy modifier the opinion of experts has been taken into account through the completion of a questionnaire. The new values are considered more realistic and accurate since the human factor is now reflected. Consequently, this improves the final risk assessment when it is applied to techniques such as QRA (Quantitative Risk Analysis). In this study, a real chemical installation, which stores flammable products, was examined using QRA and the fuzzy modifier. The introduction of the human factor through the fuzzy frequency modifier provided more conservative results than those obtained without considering this factor