Tesoro fireball caused by chemical reaction

Tesoro spokesperson Lynn Westfall has confirmed that investigators believe a series of events let to a so-called high temperature hydrogen attack, or HTHA, that caused the fireball on April 2. When asked via email if the problem could have been prevented, he told Anacortes Now "We are still investigating the historical circumstances that led to the failure that was due to HTHA, high temperature hydrogen attack. The equipment that failed was  inspected several times by outside experts in the past, none of whom recommended that it be tested for HTHA."

The belief is that hydrogen molecules get into small imperfections in the steel casing of the heat exchanger. The hydrogen then reacts with carbon in the steel, forming methane bubbles, which cause cracks in the steel, allowing the casing to break open.

Westfall said "The next steps are finishing the maintenance and repair work we started when the plant was shutdown and we expect the refinery to be operational by early October." The refinery has been shut down since a few days after the April 2 incident. Workers have stayed on the job handling maintenance work and re-building the heat exchanger that exploded.

Separate investigations are under way by the U.S. Chemical Safety Board, the state Department of Labor & Industries, the Environmental Protection Agency and the United Steelworkers Union.

The same problem was believed to be the cause of an explosion that killed 15 workers at the BP Texas City Refinery in 2005.