Key Points for Reliable LOPA

Key Points for Reliable LOPA Process hazard analyses are among the most important management system elements in the process industry for proactive risk management. Process hazard analyses must be performed starting from the design phase at facilities and the same approach must be maintained throughout the duration of operations. In many accidents experienced in the industry, improper application of process hazard analyses or system deficiencies stand out as root causes. Examples in the table can be given for accidents determined to have occurred due to ineffective process hazard analyses and lack of systematic process hazard analysis methodology [1]. Layers of Protection Analysis (LOPA) is a systematic approach used in the field of process safety to assess and reduce risks in industrial processes, particularly those involving the transport of hazardous chemicals. LOPA helps identify and evaluate protective layers aimed at preventing or reducing process-related accidents.

LOPA methodology application steps [2]

• Hazard identification, • Definition of major accident scenarios, • Acceptable risk, • Identification of initiating events, • Evaluation of conditional modifiers and enabling conditions, • Identification of Independent Protection Layers (IPL) and inclusion in calculations, • Calculation of scenario risk including existing protective measures, • Evaluation against acceptable risk level, • Documentation and reporting. In a Layers of Protection Analysis (LOPA), there are certain RED FLAGS that indicate potential problems or weaknesses in the analysis.

Critical points for correct and reliable LOPA [2]

• Inadequate Hazard Identification: Incomplete or incorrect initial hazard identification can lead to an incomplete analysis. The team can only resolve this problem through a more thorough HAZOP study. • Data Deficiency: In some cases, reliable data to support the analysis may be lacking, resulting in speculative estimates. Failure rate databases are a good reference for this issue. • Neglect of Human Factors: LOPA should consider the role of human factors in the effectiveness of protective layers. Ignoring human errors or factors can be a warning sign. CCPS has different reliability data for human error; this data can be used to determine scenario risk. • Insufficient Protective Layers: If too few independent protective layers (IPL) are considered or if the IPLs are not sufficiently reliable, this can result in underestimation of risk. • Double Jeopardy errors from HAZOP studies. • Neglect of Common Cause Failures: LOPA should consider the potential for common cause failures that could affect multiple independent protective layers. • Unclear Risk Tolerance Criteria: If the organization's risk tolerance criteria are not well defined, this can lead to uncertain outcomes and decision-making processes. Regulations or good engineering practices are good ways to resolve this issue. • Inadequate Documentation: In scenarios involving operator intervention, incomplete or incorrect SOPs and missing ITPM tasks for critical equipment can lead to incorrect evaluations in the acceptable risk approach. LOPA is the risk assessment method that provides the best compatibility with process hazard analysis methods frequently used in the process industry, such as HAZOP studies. In this context, relaxing the rules of the method used and consequently failing to take correct actions will result in facilities being in a state of false safety. Teams implementing LOPA are recommended to first conduct a correct HAZOP study to define their scenarios and required safety functions, and then take their work to the next level by collaborating with experts experienced in LOPA. Teams implementing LOPA with their own resources should review the publications by CCPS: • Layer of Protection Analysis: Simplified Process Risk Assessment, 2001. • Guidelines for Enabling Conditions and Conditional Modifiers in Layers of Protection Analysis, 2013. • Guidelines for Initiating Events and Independent Protection Layers in Layer of Protection Analysis, 2015. and apply the rules correctly.   References [1] Process Hazard Analysis, Risk Engineering Position Paper, Marsh [2] Layer of Protection Analysis: Simplified Process Risk Assessment, 2001   Mehmet Dilaver Chemical Engineer ProSCon A.Ş.