The agency's 14-minute video, "Behind the Curve," includes a 3D animation of the events that led up the explosion and includes interviews with investigators and the CSB chair.
CSB's investigation found an immediate cause of the tragedy to be a long-term, undetected high temperature hydrogen attack (HTHA) of the steel equipment, which led to the vessel rupture. The agency found the industry’s standard for determining vulnerability of equipment to HTHA to be inadequate.
In the video, investigator Lauren Grim discusses HTHA, stating: “High temperature hydrogen attack, or HTHA, – is a common hazard that has long been known within the petrochemical industry. However, Tesoro engineers and corrosion experts did not believe it could occur within the heat exchanger that ultimately failed.”
Approved in May 2014, CSB's report is one of the most extensive and complex refinery explosion investigations. The investigators also reported their findings of a substandard safety culture at Tesoro, which led to a complacent attitude toward flammable leaks and occasional fires over the years. CSB found that the complexity of the startup procedure typically required more than just the one outside operator. Yet operating procedures were not updated to account for the role of additional personnel during the hazardous non-routine work.
Visit CSB's Tesoro Refinery accident page to learn more.