Component (Non-structural): Pipe break / damage A high-pressure piping at a control station (which had not been in service for approximately 15 years) most likely cracked due to freeze on February 15, 2007, when the outdoor air temperature fell to -14 degrees Celcius (six degrees Fahrenheit).
During the cold weather prior to the incident, accumulated water in an inlet pipe elbow froze, expanded, and cracked the pipe. While the water remained frozen, the formed ice was sealing the pipe's crack. Contributing Factors Organisational: Isolation of equipment / system: Non-existentThe control station was not isolated or freeze-protected but left connected to the process, forming a dead-leg.
The dead-leg was blocked on one side by a valve that was later found to be leaking, as debris jammed the valve and prevented it from closing fully.
American Petroleum Institute (API)-recommended safety practices for oil refineries did not provide detailed guidance on freeze protection programs, nor did they sufficiently stress freeze protection of dead-legs, or of infrequently used piping and equipment.
The McKee Refinery’s freeze protection practices did not ensure that process units were systematically reviewed to identify and mitigate freezing hazards for dead-legs or infrequently used piping and equipment. Measure: Emergency shut off / safety valves: InadequateOver time, small amounts of water that were contained in the liquid propane flowed past the leaking valve and accumulated in the piping below, the lowest point formed by the control station. Other: The refinery did not conduct a management of change review (i.e., systematic reviewing of safety implications of modifications to process technology, facilities, equipment, chemicals, organizations, policies, and standard operating practices and procedures) when the control station was removed from active service in the 1990s. Consequently, the freeze-related hazards of the dead-leg formed by the control station were not identified or corrected when the change was made. | Release: Gas, vapour, mist, or smoke release to air On the day of the incident, the air temperature rose and melted the ice in the inlet pipe elbow, releasing 4,500 pounds per minute of liquid propane. Contributing Factors Measure: Emergency shut off / safety valves: Non-existentControl room operators were unable to shut off the flow of propane because remotely operable shut-off valves/emergency isolation valves were not installed in the PDA.
Although API provided safety guidance for the use of shut-off/emergency isolation valves in LPG storage installations, it did not address their use in refinery process units handling large quantities of flammable materials. Valero internal standards required the use of shut-off/emergency isolation valves in such process units, but the McKee Refinery had not retrofitted them in the PDA unit. | Fire: Vapour cloud fire / flash fire The released propane vapor cloud traveled downwind toward the boiler house where it likely ignited. The flames flashed back to the leak source and grew rapidly into fire that engulfed the area and threatened surrounding units.
The rapidly expanding fire prevented field operators from closing manual isolation valves or reaching local pump controls to isolate the high-pressure propane being vented to the atmosphere. The lack of remote isolation significantly increased the duration and size of the fire, resulting in extensive damage to the PDA, the main pipe rack, and an adjacent process unit. |
