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ANACORTES — A final report on the 2010 Tesoro refinery explosion that killed seven employees was presented and approved by the Chemical Safety Board on Thursday night in Brodniak Hall at Anacortes High School.

The report noted that problems in the facility’s safety culture, industry standards and state and federal oversight of the industry helped lead to a catastrophic rupture of a heat exchanger at the refinery, which leaked and ignited hydrogen and naphtha, a flammable petroleum solvent.

A draft report detailing investigation findings and recommendations was released by the board in January.

After receiving input from the United Steelworkers, the American Petroleum Institute, the Western States Petroleum Association, American Fuel and Petrochemical Manufacturers and a list of other stakeholders in industry operations and regulation, the board made a few substantial revisions to the report in its final form.

The explosion was caused by High Temperature Hydrogen Attack or HTHA, which severely cracked and weakened carbon steel tubing leading to a rupture, according to the report.

The report found the carbon steel tubing that burst in the heat exchanger due to HTHA was estimated to be operating within the petroleum industry’s current Nelson Curve for that material.

Nelson Curves are industry guidance documents used to predict and manage HTHA damage based on the heat and pressure a material is exposed to.

The final report recommended establishing a much more conservative Nelson Curve for carbon steel, prohibiting the use of the material in processes that operate in temperatures above 400 degrees Fahrenheit and 50 pounds per square inch of pressure.

The final version also changed recommendations made to the state of Washington.

Instead of advocating the state develop and implement a specific model to improve process safety in Washington refineries, the board recommended the state adopt more rigorous process safety management attributes and features based on the team’s regulatory analysis.

Features of this improved process safety management model include development of a more comprehensive process hazard analysis and establishing a well-funded, well-staffed and technically qualified regulator who can perform preventative audits and inspections.