The April 2010 fatal explosion and fire at the Tesoro refinery in Anacortes, Washington was caused by damage to the heat exchanger, a mechanism known as “high temperature hydrogen attack” or HTHA, which severely cracked and weakened carbon steel tubing leading to a rupture, according to a Chemical Safety Board (CSB) draft report released today. The draft report makes far-reaching recommendations to the EPA and the governor and state legislature of the State of Washington to more rigorously protect workers and communities from potentially catastrophic chemical releases. 

A clarion call for refinery safety reform

“Seven lives were tragically lost at the Tesoro refinery in 2010,” said Dr. Rafael Moure-Eraso, CSB chairperson. “I believe the draft report does an outstanding job of tracing this complex accident to its roots: a deficient refinery safety culture, weak industry standards for safeguarding equipment, and a regulatory system that too often emphasizes activities rather than outcomes. The report is a clarion call for refinery safety reform.”

Superviser asked for help; all died

Using sophisticated computer models, the investigation found the industry-wide method used to predict the risk of HTHA damage to be inaccurate, with equipment failures occurring under conditions the deemed to be safe from HTHA. It cited deficiencies in the company’s safety culture that led to a “complacent” attitude toward flammable leaks and occasional fires. Investigators also determined that during the unit startup, Tesoro did not correct the history of hazardous conditions or limit the number of people involved in the hazardous non-routine startup of the heat exchangers. But because of the reoccurring leaks and the need to manually open a series of long-winded valves that required over one hundred turns by hand to fully open, a supervisor requested five additional workers to help. All seven lost their lives as a result of the blast.

CSB Chairperson Dr. Rafael Moure-Eraso said, “The accident at Tesoro could have been prevented had the company applied inherent safety principles and used HTHA resistant construction materials to prevent the heat exchanger cracking. This accident is very similar to the one that occurred at the Chevron refinery in Richmond, California in August 2012, where corrosion of piping went undetected for decades until it ruptured, endangering the lives of 19 workers caught in a vapor cloud and sending 15,000 community members to the hospital. Companies must do a better job of preventing refinery accidents, which occur all too frequently.”

API data unreliable

The draft report notes that recommended practices of the American Petroleum Institute, the leading industry association, are written “permissively” with no minimum requirements to prevent HTHA failures. For example, API Recommended Practice 941 --- Steels for Hydrogen Service – uses the term “should” 27 times and “shall” only once. It also does not require users to verify actual operating conditions in establishing operation limits of the equipment or to confirm that the materials of construction selection will prevent the damage. An inspection strategy that relied on design operating conditions rather than verifying actual operating parameters contributed to the accident.

The investigation found Tesoro, like others in the industry, use published data from the American Petroleum Institute, called the Nelson Curves, to predict the susceptibility of the heat exchangers to HTHA damage. The CSB found these curves unreliable because they use historical experience data concerning HTHA that may not sufficiently reflect actual operating conditions. For example, a CSB computer reconstruction of the process conditions in the exchangers determined that the portion of the carbon steel exchanger that failed likely operated below the applicable Nelson curve—indicating it was “safe.”  

The CSB determined that inspections for such damage are unreliable because the microscopic cracks can be localized and difficult to identify. The report concludes, “Inherently safer design is a better approach to prevent HTHA.” It notes that API has identified high- chromium steels that are highly resistant; these were not installed by Tesoro. The CSB has called for the adoption of inherently safer technology, design and equipment in other reports, notably the Richmond, California, Chevron refinery fire of August 2012.