On February 1, 2025, around 1:36 p.m., an explosion and fire occurred at a refinery in California. It was estimated that the incident caused approximately $924 million in property damage.
On February 1, 2025, the refinery tasked contract workers with installing an isolation blind at Flange A to prepare a catalytic feed hydrotreater unit (“unit”) for turnaround maintenance. A yellow tag was placed between Valve 2 and Valve 3 to indicate the location of the blind installation. After completing a field walkthrough to verify that the piping segment between Valve 1 and Valve 2 was empty, an operator issued a permit to the supervisor of the contractor work crew at 11:30 a.m.
When the work started, two contract workers were on a scaffold that provided access to the elevated equipment. In addition to their standard protective equipment, the two workers wore supplied-air respirators. Two standby workers from a different contract company were at ground level to monitor the breathing air equipment and observe the flange opening work. At approximately 1:25 p.m., the two contract workers began unbolting Flange B. At this time, neither the workers’ supervisor nor the operator who issued the permit for the contractors to install the blind was present.
As Flange B was being unbolted, the contract workers’ supervisor returned to the work area. From his vantage point, the supervisor could not see which flange the crew was working on. Shortly thereafter, the supervisor observed and heard a pressurized release and recognized that something was wrong. One of the standby workers activated an air horn to stop the work. The two contract workers disconnected from their supplied-air hoses, jumped from the scaffold, and evacuated the area. At about 1:30 p.m., the flammable material ignited and exploded with flames erupting from the area. Hot (above 600 degrees Fahrenheit) hydrocarbon material continued to be released from Flange B, fueling the fire. The extent of the fire escalated over three days and involved other equipment until emergency responders extinguished the fire on February 4, 2025. The company reported that approximately 50,000 gallons of flammable hydrocarbon material were released over three days.
The company’s investigation found that the contract workers, hired specifically for the extra tasks during the turnaround, had not received training on the refinery’s equipment opening policies and procedures. Consequently, these workers were not aware of the company's tagging system for identifying which flange should be opened. The company’s investigation also revealed that installing this blind should have been treated as a “first break” (as written on the permit) under the refinery’s policies, because this was the initial equipment opening for this system. First breaks required a qualified operator to be present during the work to ensure that maintenance workers open the proper equipment. However, because of a miscommunication between the workers, the operator was not present when the contract workers disassembled Flange B.
The company required maintenance crews to attach their personal locks or tags to all valves used for equipment isolation. The contractor crew did not apply locks or tags to Valve 1 or Valve 2. If the crew had done so, they could have had the opportunity to better understand the existing hazards by participating in the lockout/tagout process for these valves. The permit issued to the contractor supervisor stated that the equipment was out of service. The supervisor believed that all the equipment was empty and was unaware of the active (operating) process adjacent to Valve 2.
Because the work was on a scaffold, laser pointers were used to highlight Flange A during the field walk-throughs involving the operator, contract workers, and the contractor’s supervisor. Although post-incident interviews with the operator and the contractor’s supervisor revealed that two of the four walkdown participants understood that the blind should be installed in Flange A, it is evident that the contract workers believed that Flange B was the correct location.
Following the incident, the company revised its permitting procedure. For permits that require an operator to be present, operators must now issue one permit per isolation blind only after the workers are at the job site and prepared to start the task. This change was made to help ensure an operator is present to confirm that work is performed on the correct equipment.
Probable Cause
Based on the company's investigation, the CSB determined that the probable cause of the incident was the opening of a flange that was connected to an active process containing pressurized flammable liquid hydrocarbon. When the flange was loosened, the flammable material was released and ignited (autoignition or static discharge), resulting in a large fire. The company could have prevented the incident by having a knowledgeable person present to ensure that workers unfamiliar with the equipment disassembled the correct flange and were aware of the existing hazards. Additionally, the company would benefit from improving its tagging practice to make it obvious which equipment workers should disassemble.
Source:CSB.gov
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