OREANDA-NEWS. An investigation into the cause of a February explosion that injured four contract workers at ExxonMobil's 155,000 b/d refinery in Torrance, California, will keep a major source of southern California gasoline shut down for months.

Torrance refinery manager Brian Ablett deferred questions about the timing of the equipment restart during a state senate hearing on the root cause of an 18 February blast that ripped open environmental equipment associated with a fluid catalytic cracking (FCC) unit and coated the surrounding area with the ashy remains of spent catalyst. Ablett, who became manager of the facility less than a year ago, would not guess how long an investigation into the cause of the blast would take, other than to say he expected it to last for months.

The FCC will remain shut until state regulators certify the equipment is safe to operate. The company said others parts of the refinery continue to operate.

Ablett also told state senators and a small, somewhat adversarial crowd gathered in a Torrance community center that was webcast last night that it was no surprise or concern that the cause of the explosion on such complex equipment was not immediately known.

"I understand the need for speed, but if we don't truly understand what happened and why it happened, we're not going to position ourselves well to ensure it doesn't happen again," Ablett said.

Investigators know that an electrostatic precipitator (ESP), a device common to modern refineries that removes particulate and other contaminants from gas produced by an FCC, overpressurized and exploded. But state and company officials have not yet determined why. Such a finding will be important to state authorities certifying ExxonMobil to restart the FCC and resuming gasoline production.

Investigating agencies worked for eight months before authorizing a restart of a crude unit involved in an August 2012 fire at Chevron's 225,000 b/d refinery in Richmond, California.

Dave Campbell, an organizer with United Steelworkers (USW) Local 675 who was not at the refinery at the time of the explosion, said many more workers could have been injured or killed if a coffee break at the time had not already cleared the area and an operator not quickly sounded an alarm.

USW workers began a 1 February work stoppage that has since spread to 20pc of US refining capacity — but not the Torrance facility — amid national negotiations over the use of non-union employees, wages and benefits.

"Had it not been for the fact that it was coffee break time, a good chunk of our union leadership would have been involved in that accident," Campbell said.

The four contractors injured in the blast were not working directly on the unit at the time, Campbell said. Two were truck drivers wearing hearing protection that made them unable to hear evacuation alarms.

ExxonMobil did not have an immediate comment on Campbell's remarks.

Ablett and inspectors faced an audience skeptical of assurances that the material cast into surrounding neighborhoods was not toxic or dangerous. Elected leaders worried that, without knowing the cause of the explosion, other refineries risked similar accidents on their ESPs. US representative Ted Lieu today formally requested a US Chemical Safety Board investigation into the accident. State senator Isadore Hall III, whose district includes Torrance, warned that ExxonMobil's stated commitments to determining the cause and preventing similar accidents in the future was not enough.

"Your testimony, to me, it's not convincing," Hall said to applause. "We're going to be holding you accountable and we're going to be making sure that you respond to this incident."