- Screenshot via KCAL.

Screenshot via KCAL.

ExxonMobil must comply with a subpoena issued by the U.S. Chemical Safety Board demanding information about containing hydrofluoric acid on the site of a 2015 oil refinery explosion in Torrance, California, the Ninth Circuit Court of Appeals ruled Monday.

On Feb. 18, 2015, an explosion in a fluid catalytic cracking unit in ExxonMobil's Torrance refinery caused a release of flammable hydrocarbons and ash mixed with metal, fiberglass and glass wool debris. Four workers were injured, and ExxonMobil closed the cracking unit for 15 months for repair.

In the course of its investigation, the U.S. Chemical Safety Board issued seven subpoenas with a total of 380 requests for information. ExxonMobil refused to comply with 56 of those requests. ExxonMobil argued that information about hydrofluoric acid was irrelevant to the investigation because it was not involved in the cracker explosion.

"Correctly interpreting the Board's statutory authority and applying the generous relevance standard, the five requests whose denial the Board appealed are relevant to the Board's investigation of the February 2015 accidental release," the Ninth Circuit ruled.

The explosion caused a 40-ton piece of debris from the fluid catalytic cracking unit to fly approximately 100 feet, landing in the adjacent alkylation unit. The debris landed within five feet of a "settler," or tank, filled with modified hydrofluoric acid, a highly corrosive liquid that is toxic if released.

The CSB is authorized to "investigate (or cause to be investigated), determine and report to the public in writing the facts, conditions and circumstances and the cause or probable cause of any accidental release resulting in a fatality, serious injury or substantial property damages," the ruling states.

In a final report on the explosion issued in May 2017, the CSB describes multiple gaps in the refinery's process safety management system, allowing for the operation of the FCC unit without pre-established safe operating limits and criteria for a shut down. The refinery relied on safeguards that could not be verified and re-used a previous procedure deviation without enough hazard analysis of the current process conditions.

In July 2016, the Torrance refinery was sold by ExxonMobil to PBF Holdings Company, LLC, which now operates as the Torrance Refining Company.