Case Studies and Discussion
- Case Study 1: Runaway Reaction in a Crude Distillation Unit (CDU)
Incident: At an oil refinery, a runaway reaction occurred in the Crude Distillation Unit (CDU) due to a series of failures. The root cause was traced back to inadequate management of change (MOC) procedures. A new temperature sensor was installed in the CDU without a thorough evaluation of its impact on the overall process control system. This resulted in faulty temperature readings, leading to an excessive influx of crude oil into the CDU column. The distillation process became unstable, causing a runaway reaction and a release of hydrocarbons.
PSM Learnings: This incident highlights the importance of a stringent MOC program. All changes, even seemingly minor ones like sensor replacements, must be rigorously assessed for potential safety implications. This includes evaluating the compatibility of new equipment with existing control systems and performing simulations to predict process behavior under various conditions.
- Case Study 2: Tank Overflow and Fire at a Storage Terminal
Incident: A storage tank overflow incident occurred at an oil refinery terminal, resulting in a significant fire. The incident stemmed from a malfunctioning level gauge on the storage tank. The faulty gauge provided inaccurate readings, indicating empty space when the tank was nearing capacity. Operators continued transferring oil into the tank, unaware of the impending overflow. The tank eventually overflowed, and the released oil ignited due to an unidentified ignition source.
PSM Learnings: This case study emphasizes the importance of proper instrument calibration and maintenance within a PSM program. Regular calibration of critical instruments like level gauges ensures accurate process data and prevents misleading information from reaching operators. Additionally, having robust procedures for verifying tank capacity before transfers and implementing high-level alarms on tank gauges can serve as secondary safeguards to prevent overflows.