A fuzzy-HAZOP/ant colony system methodology to identify combined fire, explosion, and toxic release risk in the process industries

•A new method is introduced to evaluate fire, explosion, and toxic release risk in the process industries.•The method integrates Fuzzy set theory and Ant Colony System (ACS) approach.•ACS was used to optimize the rules used in the analysis.•The results show that the method outperforms the fuzzy set method when evaluating a gas refinery risk.•Extended fuzzy HAZOP method was used to identify process parameter deviations. This study introduces a hybrid approach that merges a fuzzy HAzard and OPerability (fuzzy-HAZOP) technique, an Ant Colony System (ACS), and fuzzy set theory to evaluate the coupling of fire, explosion, and toxic release risk in the process industries. The fuzzy-HAZOP technique enhances the evaluation of process deviation risks by incorporating other, fundamental, aspects of risk. The ACS method is applied to provide comprehensive rules that take into account the complex relationships between operative parameter deviations, safety control failures, and the fuzzy set theory is used to reduce vagueness, ambiguity, inaccuracy, and uncertainty in expert assessments. Our hybrid method is applied to an example from the gas refinery industry. The results show that it outperforms the fuzzy set method when evaluating joint fire, explosion, and toxic release risk. Our approach is not only practical, but experts can also apply it in other industries where there is a need to assess joint fire, explosion, and toxic release risk.