Quantitative Risk Assessment (QRA) of Major Accident Hazards in a Petrochemical Refinery Using Fault Tree and Consequence Analysis

Abstract

The relentless expansion of the Chemical Process Industry (CPI) necessitates the implementation of rigorous and comprehensive safety evaluations. This research manuscript presents an extensive Quantitative Risk Assessment (QRA) conducted on a major petrochemical refinery, specifically targeting the hazards associated with the storage and processing of highly volatile and toxic substances. Integrating Hazard Identification and Risk Assessment (HIRA), Failure Mode and Effects Analysis (FMEA), and Fault Tree Analysis (FTA), this study establishes a robust methodological framework for assessing industrial risk. A systematic screening process utilizing IPO (Inter Provinciaal Overleg) A-factor and S-factor metrics was deployed to isolate the most severe major accident hazard (MAH) installations, culminating in the selection of pressurized Liquefied Petroleum Gas (LPG) and Propylene Horton spheres, large-scale Naphtha storage tanks, and Hydrogen Sulphide (H2S) transfer pipelines. Advanced mathematical consequence modeling was executed, comprising TNT equivalency methods for Vapour Cloud Explosions (VCE), semi-empirical thermodynamic models for Boiling Liquid Expanding Vapour Explosions (BLEVE), and the Pasquill-Gifford dispersion model for toxic gas plumes. The consequence analysis revealed that a catastrophic failure of a 1,200 MT LPG Horton sphere generates a fireball 616.3 meters in diameter, emitting lethal horizontal thermal radiation fluxes (109 kW/m²) that extensively impinge upon vulnerable off-site residential boundaries. Furthermore, the synthesis of FTA-derived failure frequencies (3.6E-7 per year for Horton spheres) with local demographic data demonstrated that the societal risk (F-N curve) breaches the universally accepted ALARP (As Low As Reasonably Practicable) thresholds. The findings underscore the acute vulnerability of densely populated regions adjacent to legacy pressurized storage facilities. The manuscript concludes by presenting concrete, inherently safer design recommendations, advocating strongly for the phase-out of above-ground spheres in favor of mounded bullet technology, alongside the enhancement of Safety Instrumented Systems (SIS) and stringent land-use zoning.