The British Petroleum (BP) American Refinery accident, back in 2005, was one of the most severe explosions recorded in any industrial accident database. According to both the reconstruction and the interviews with the company, it was found that the causes of the accident where both technical, with the failure of a level controller, which was also badly designed for the isomerization unit, and human, with a very stressed and undersized personnel.
In this work, a Quantitative Risk Assessment (QRA) based on the Recursive Operability Analysis (ROA), as hazards and accidental scenarios identification tool, was performed on the unit (BP isomerization unit) involved in the accident. The analysis was carried out exploiting many different techniques, to provide a proper assessment. The quantification of all node-deviation-variables (necessary to establish the real behaviour of the system) was performed by implementing the BP plant in CoCo simulator.
Basic events were identified using a simplified Failure Mode and Effects Analysis (FMEA). Then, the magnitude of fire and explosion was estimated basing on the simulation results provided by the ALOHA software. Finally, a Fault Tree Analysis for the BP isomerization unit was performed, quantifying the probability of occurrence of all the most credible scenarios. Probabilities, magnitudes, and risk indexes (function of the distance with respect to the source point) were also estimated. From the analysis, the importance of redundant measurements of the most crucial variables, such as liquid level, and the impact of human errors was highlighted.