The US Chemical Safety Board will fully investigate what caused an Aug. 6 fire at Chevron USA Inc.’s 240,000 b/d Richmond refinery in Martinez, Calif., CSB announced on Aug. 11.
A team of seven investigators arrived at the plant northeast of San Francisco on Aug. 8 and has interviewed witnesses and reviewed documents, CSB said. Structural and safety experts were due to arrive on Aug. 13 to prepare for investigators’ safe entry into the fire area, it added.
The fire occurred when gas oil leaked from an 8-in. pipe connected to a crude oil distillation tower, according to CSB. It said workers noticed the leak and were attempting repairs on piping connected to the still-operating distillation tower when the leak suddenly intensified. With temperatures more than 600° F. of material in the tower, the leaking gas oil immediately formed a large flammable vapor cloud, CSB said.
“Witness testimony collected by CSB investigators indicates that a large number of workers were engulfed in the vapor cloud,” said Dan Tillema, the investigation team’s leader. “These workers might have been killed or severely injured, had they not escaped the cloud as the release rate escalated and the cloud ignited shortly thereafter.”
Important issues in the investigation included understanding why the pipe that later failed was kept in service during a late-2011 maintenance turnaround and what procedures and industry practices exist for responding to a leak of combustible material from a running unit, Tillema said.
The board anticipates executing a site preservation and evidence testing agreement with Chevron and other investigative groups, and arranging for independent testing of the leaking section of pipe to determine the failure mechanism, Tillema indicated.
CSB said both Chevron and the United Steelworkers, which represents hourly workers at the plant, have been cooperating with the investigation. Chevron has provided assurances its personnel will freely share their knowledge and investigative information with the Board. Cal/OSHA, Contra Costa County, the US Environmental Protection Agency, and other investigative groups are fully cooperating, CSB said.
Its announcement came days after the refinery filed an initial report on the incident with the Contra Costa County Department of Health Services as part of the county’s 72-hr notification policy.
The Aug. 9 report said the fire occurred at about 6:30 p.m. PDT near P-1149, a C-100 atmospheric column which currently is not operational. The nearly 2.1 MMscf flare initially included 739 lb of sulfur dioxide, 87 lb of methane, and 1,270 lb of non-methane hydrocarbons, it said.
Employees reported five minor injuries, three associated with the incident; received first aid; and returned to work on the same shift, the report said. No contractor employee injuries were reported. Chevron said it established a claims process to compensate the refinery’s neighbors for medical and property expenses from the fire.
Five Chevron employees were deployed outside the refinery on Aug. 6 to take 17 direct air quality samples downwind of the fire, which showed nondetectable hydrogen sulfide, sulfur dioxide, and carbon monoxide concentrations, the report continued. Other local air quality monitors showed potentially toxic pollutant levels well below their reference exposure levels and not a significant health concern, it said.
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