Assessment of Nitrogen Purging Criteria for Refinery Commissioning Using Limiting Oxygen Concentration and Failure Mode and Effects Analysis

Purpose: This study evaluates the safety and operational implications of revising the oxygen acceptance criterion for nitrogen purging from below 0.5% to below 1% during refinery commissioning. The objective is to determine whether the revised criterion can reduce nitrogen consumption and direct cost while maintaining an adequate safety margin. Methodology: A quantitative case-study design was applied to a fuel-gas transfer system within a large-scale refinery development project in Indonesia. The study compared a design-based baseline criterion of below 0.5% oxygen with a field-implemented criterion of below 1%. Data included oxygen concentration, purging pressure, number of cycles, nitrogen volume and mass, and direct nitrogen cost. Batch-purging calculations, field measurements, Limiting Oxygen Concentration (LOC) analysis, cost comparison, and Failure Mode and Effects Analysis (FMEA) were employed. Results: The revised criterion was achieved after six purging cycles with a measured oxygen concentration of 0.96%, whereas the baseline criterion required eight calculated cycles. Nitrogen consumption decreased from 3,000 to 2,381.25 m3, generating direct cost savings of IDR 25,059,375 or 20.62% per system. FMEA identified single-point oxygen sampling as the highest-priority risk with an initial Risk Priority Number (RPN) of 240. Conclusion: The revised criterion improved nitrogen-use and cost efficiency while remaining below the lowest applicable LOC under the evaluated conditions. Its implementation requires multi-point oxygen measurement, system-specific procedures, and competent personnel. Originality: This study integrates field measurement, process-safety evaluation, engineering cost analysis, and structured risk assessment in determining an oxygen acceptance criterion for refinery commissioning.