Integrated HAZOP/LOPA Method to Determine Safety Integrity Level (SIL)

The goal of the study is to adapt and develop the integrated HAZOP/LOPA method to promptly assess the safety integrity level of safety functions in a single session. During the study, the advantages and disadvantages of the integrated approach were systematized, and practical recommendations for joint use of the qualitative Hazard and Operability Study (HAZOP) method and the semi-quantitative risk assessment Layer of Protection Analysis (LOPA) method were elaborated, preserving the key benefits of HAZOP, that are, the systematic approach combined with the creative nature of the hazard identification process. The proposed method is illustrated using an example of a petrochemical facility. The main scientific and practical results of the study are as follows. A critical analysis and systematization of the key advantages and disadvantages of the integrated method were conducted, providing specialists with the necessary grounds to make a decision regarding its use. Within the modification of the approach, primarily, a hazardous event, that is, an emission or unit destruction, is to be adopted as the endpoint of the scenario analysis. This helps to exclude conditional modifiers associated with potential conditions of scenario development after the emission and focus on the hazard identification during the session. Secondly, the risk reduction matrix from GOST R EIС 61511-3—2018 Functional Safety. Safety instrumental systems for industrial processes. Part 3. Guidance for determining required safety integrity levels” was integrated as a unified basis to establish permissible risk criteria. A set of practical recommendations on the optimization of HAZOP/LOPA was developed, that included the use of the cause-by-cause documentation method, determining a hazardous event as the endpoint of the scenario (for example, accidental leakage of a unit or hazardous substance emission), selective use of the LOPA approach, inclusion of a LOPA specialist in the working group, and the requirement for moderator’s competencies in both methodologies. It is important to emphasize the limited applicability of the approach to scenarios in which a harmful event (injury, fatality) rather than a hazardous event is used as the endpoint of analysis. This is specifically relevant if the permissible risk criteria for certain scenarios are established by the distribution of permissible individual or social risk among them. In such cases, conditional modifiers might be considered, which can lead to a disproportionate increase in session duration and a shift of focus from hazard identification to discussions of accident development, which contradicts the basic principles of HAZOP.