CSB: Release, Fire Occurred during Unit Startup at Renewable Diesel Facility
Overheating of a fired heater caused a metal tube to rupture, releasing hot renewable diesel and hydrogen and leading to a fire that seriously injured one worker at a facility in California in 2023, according to the final report on the incident from the U.S. Chemical Safety and Hazard Investigation Board (CSB). The incident occurred in the Marathon Martinez Renewables facility’s renewable diesel hydroprocessing unit, which was being started up for the first time to manufacture renewable diesel. CSB describes renewable diesel as a type of renewable fuel that has properties similar to conventional diesel and is made from “feedstocks of fats, soybean oil, corn oil, and greases.” Growing demand for renewable diesel and other renewable fuels had prompted four of California's 13 refineries to convert to renewable fuel production as of early 2024, the agency explains.
Technical failures and unsafe operational practices at Marathon Martinez contributed to the incident, CSB says. The agency identified two safety issues that led to the overheating and rupture of the tube: a misaligned valve that was open when it should have been closed, allowing process material to bypass the heater, and blocked air supply to burners, leading to improper air-fuel mixing. Additional safety issues that contributed to the severity of the incident were the facility’s lack of effective alarms to alert staff that tube metal temperatures had exceeded safe limits and the failure of the facility’s safety instrumented system to detect low-flow conditions when process material was diverted through piping downstream of the flow meter. The worker who was seriously injured, a field operator who was sent to turn off individual burners while personnel attempted to troubleshoot the issues rather than shut down the heater remotely, was right next to the heater when the release and fire occurred. According to CSB’s report, the worker suffered third-degree burns to over 80 percent of his body and was in critical condition for months.
“This tragic event underscores the importance of having proper safeguards in place for fired heater operation, which can be particularly hazardous,” CSB Chairperson Steve Owens said in a news release. “A series of safety failures contributed to the severity of this incident, including the lack of appropriate guidance for when to shut down the heater remotely instead of putting a worker at risk of harm.”
The CSB report outlines several recommendations to the Marathon Martinez Renewables facility, Marathon Petroleum Corporation, and the American Petroleum Institute (API). The agency recommends that the facility implement engineering safeguards to detect and prevent afterburning in the fired heater that was involved in the 2023 incident. Marathon should update its corporate safety standards to include guidance for alarming tube metal temperatures and to specify when workers should be removed from an area when safe limits are exceeded, the agency says. CSB also urges API to update the standard API RP 556, Instrumentation, Control, and Protective Systems for Gas Fired Heaters, to include requirements for responding to high tube metal temperatures.
CSB’s final report is available as a PDF. Additional information about the incident can be found on the agency’s website.
