The U.S. Chemical Safety Board said a fireball of hydrogen and naphtha engulfed seven workers at Tesoro Corp.'s Anacortes, Washington refinery in 2010 because the company failed to identify the damage hydrogen was causing to steel components, according to a draft report released on Thursday.
Further, the CSB said industry practices recommended by the American Petroleum Institute don't require refiners to take necessary steps to prevent high-temperature hydrogen attacks that form minute cracks in carbon steel like that on the heat exchanger which ruptured at the Tesoro Anacortes refinery on April 2, 2010.
The board plans to vote on a final version of the report this year.
In a statement, Tesoro acknowledged the efforts of board investigation teams "despite the significant and successive turnover in the agency's assigned personnel over the years".
However, the company said it would discuss disagreements with the board over the probe's findings once the report is approved by the CSB.
"We respectfully disagree with several findings in the draft report and, most importantly, take exception to CSB's inaccurate depiction of our process safety culture," Tesoro said.
The CSB also said the Washington State Department of Labor & Industries, which regulates workplace safety, needed tougher standards and should perform a safety audit of the state's five refineries.
The report suggests Washington state switch its regulatory system to one like that in the United Kingdom which requires use of the safest possible technology.
A similar recommendation for California by the board staff led to sharp disagreements among the board's three members at a public meeting in Richmond, California on January 15. Two board members said such a radical overhaul would not ensure safer refineries and chemical plants.
In the report about the Anacortes, Washington blast released on Thursday, the CSB also said the U.S. Environmental Protection Agency does not enforce the use of inherently safer technology, but could do so under its current powers.
Use of inherently safer technology was the surest way to prevent accidents like the rupture of piping on a naphtha hydrotreater heat exchanger at the Anacortes refinery, board Chairman Rafael Moure-Eraso said in a statement.
"The accident at Tesoro could have been prevented had the company applied inherent safety principles and used high-temperature-hydrogen-attack resistant construction materials to prevent the heat exchanger cracking," Moure-Eraso said.
The 2010 Tesoro Anacortest explosion was the deadliest at a U.S. refinery since the 2005 explosion at a Texas City, Texas, refinery then owned by BP Plc.. Fifteen workers were killed in the BP explosion and 180 others were injured.
Five workers caught in the Anacortes refinery fireball died on the day of the explosion. Two other workers died within the following month.
The seven workers were checking for leaks and helping with the start-up of another, nearby heat exchanger when piping on a heat exchanger in operation suddenly failed, engulfing them in a fireball.
In a separate investigation completed six months after the blast, the Washington Department of Labor & Industries found the explosion was preventable, but came about because Tesoro did not stick to its own guidelines for maintaining equipment.
The Chemical Safety Board investigates fires and explosions at U.S. chemical facilities. It does not possess regulatory or law enforcement authority. It does make recommendations to governments and industries about improving practices and standards.
(This version of the story was corrected to read "did not" in paragraph 16)
(Reporting by Erwin Seba in Houston; Editing by Matt Driskill and Jason Neely)