Fundamental process safety management errors—some common to all U.S. refineries—led to a 2015 accident at an ExxonMobil refinery in Torrance, Calif., says a May 3 report from the U.S. Chemical Safety Board.
ExxonMobil’s lack of proper protocol to manage risk meant “workers were essentially running the unit blind,” says CSB Chairwoman Vanessa Allen Sutherland.
The accident injured four workers, none seriously. The explosion sent debris flying, with some landing near tanks of hydrofluoric acid (HF). Many refineries use this highly toxic chemical in the alkylation process.
The explosion occurred in the electrostatic precipitator, part of the refinery’s air pollution control system. Undetected hydrocarbons back-flowed through piping from the fluid catalytic cracking unit and ignited in the precipitator, CSB determined. At the time of the incident, the cracking unit was shut down for planned maintenance but was not sufficiently isolated from the rest of the facility, the report says.
The refinery lacked hydrocarbon detection equipment that might have flagged the leak, CSB says. The absence of such equipment is an industry-wide problem, it adds.
The accident shut down the refinery and cut output for more than a year. It also heightened fears of some 150,000 nearby residents.
HF is used in about one-third of the some 150 refineries in the U.S. It can seriously injure or kill even in small concentrations.
CSB is also investigating the potential impact if debris had hit the HF storage tanks. However, ExxonMobil, which recently sold the refinery to PBF Energy, has withheld the information CSB asked for, saying this aspect of the probe exceeds board’s authority.
The company tells C&EN there is no evidence the incident posed any risk to the community.
Following this incident and four others since the 2015 accident, regional regulators in California have launched a study to consider substitutes for HF at refineries. They are aiming to release their findings by year’s end.
CORRECTION: This story was updated on May 4, 2017, to remove the characterization of HF as a gas that’s heavier than air.
This story was updated on May 24, 2017, to correct the name of PBF Energy, the company that purchased the refinery from ExxonMobil.