The US Chemical Safety Board (CSB) will pursue a full investigation to determine the causes of last weeks fire at the 245,000 bpd Chevron refinery in Richmond, California, the agency announced on Monday.
A CSB team with seven investigators arrived at the refinery last Wednesday and has since been conducting witness interviews and reviewing documents at the site.
CSB structural and industrial safety experts will arrive at the site later Monday to prepare for safe entry by investigators into the immediate area of the fire, the agency said.
The fire occurred when a combustible hydrocarbon liquid known as gas-oil leaked from an eight-inch pipe connected to a crude oil distillation tower in the refinerys crude unit.
Workers initially noted the leak and were in the process of attempting repairs on piping connected to the still-operating crude oil distillation tower when the leak suddenly intensified.
Due to the high temperature of the material in the tower, in excess of 600 degrees Fahrenheit, the gas-oil immediately formed a large flammable vapor cloud.
Witness testimony collected by CSB investigators indicates that a large number of workers were engulfed in the vapor cloud, said CSB team lead Dan Tillema, P.E.
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.
CSB chair Dr. Rafael Moure-Eraso called the fire a near-disaster for refinery personnel.
The circumstances warrant a full and independent federal investigation to determine the root causes, Dr. Moure-Eraso said. Although fortunately no workers were killed, the overall impact of the incident ranks it as among the most serious US refinery incidents in recent years.
CSB board member Mark Griffon, who accompanied the investigators, said information gathered so far indicates the incident had a serious impact on the community.
Area hospitals told CSB investigators that they attribute hundreds of emergency room visits by community members to reported effects of the release and fire, with symptoms ranging from anxiety to respiratory distress.
Mr. Tillema said important issues in the investigation include 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.
He said the CSB 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.
Both Chevron and the United Steelworkers, which represents hourly workers at the plant, have been cooperating with the CSB team, the agency said.
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 also fully cooperating, according to the agency.