An explosion and fire ripped through a gasoline processing unit at an Exxon Mobil refinery in Torrance, California, 20 miles south of Los Angeles on Wednesday, slightly injuring four workers and shattering windows of surrounding buildings, authorities said.
Investigators were trying to determine the cause of the blast, which occurred shortly before 9 a.m. PST, but there was no evidence of foul play, according to Torrance Fire Captain Steve Deuel.
Deuel said a small ground fire following the explosion was quickly extinguished. Firefighters and refinery crews also contained a gasoline leak caused by the blast, he said.
"All personnel have been accounted for," Exxon Mobil said in a statement. "Four contractors have been taken to Long Beach Medical Center for evaluation for minor injuries."
Earlier, Torrance Mayor Patrick Furey told local television station KNBC that people who live near the refinery should take precautions.
"The most important thing is to shelter in place, stay indoors, no outdoor activity, turn the air conditioners off, keep the windows closed," Furey told the station.
A structure at the refinery was visibly damaged, with smoke smoldering from twisted metal, and the air near the blast site smelled of sulfur and chemicals.
The South Coast Air Quality Management District dispatched inspectors to take air samples for analysis "as quickly as possible," said agency spokesman Sam Atwood.
The agency issued a health advisory urging children, the elderly or individuals with respiratory or heart conditions to stay indoors if they can see or smell smoke and for otherwise healthy people to avoid strenuous activity outdoors if they can see or smell smoke.
The California Department of Industrial Relations opened a probe into the blast, agency spokeswoman Julia Bernstein said.
The workplace safety agency issued an order forbidding Exxon Mobil from operating the 100,000-barrel-per-day fluid catalytic cracker – a central gasoline-producing unit – until the investigation is complete, Bernstein said. The department said the shutdown of the unit could last up to six months.
The refinery has a capacity of 155,000 barrels per day, according to Exxon Mobil.
Gasoline in Los Angeles surged to the highest level in about 18 months after the explosion on fears that local supply will tighten in the weeks ahead. The surge could translate to higher pump prices just as Californians and other U.S. motorists are benefiting from the slump in crude oil prices.
The fluid catalytic cracker is the facility's main gasoline producing unit. Tesoro Corp recently shut its nearby 240,000-barrel-per-day refinery in Martinez after United Steelworkers union members walked out.
Cory Milsap, an electrical contractor at the plant, said many workers were sent home after the explosion. The refinery occupies 750 acres and has 650 employees and 550 contractors.
"All I heard was a loud sound…all I saw was smoke and people running, so I made sure I got out of there," Milsap said.
Giselle Monreal, who lives across the street from the facility, said the blast shook the ground like an earthquake, knocking a 52-inch flat-screen television off its stand onto a coffee table and shattering a window in her garage.
Surrounding areas were not evacuated, but nearby schools kept students and staff indoors immediately after the explosion as a precaution, Fire Captain Deuel said.
Students at 14 schools near the refinery were ordered to shelter in place because of concerns over air quality, Torrance Unified School District spokeswoman Tammy Khan told Reuters.
Exxon was looking into the cause of the explosion, according to Gesuina Paras, a public and government affairs adviser at the company.
Trade publication OPIS, citing an unidentified source, reported that an electrostatic precipitator (ESP), which reduces fluid catalytic cracker particulates, exploded as contract workers were doing maintenance on the nearby fluid catalytic cracking unit, or FCC.
"Contractors working on the FCC to fix the expanders," the source said, adding that an injection of ammonia on top of the flue gas stream caused a pressure buildup, which resulted in the ESP unit explosion.
The unit could take up to a year to replace, the source said.
The incident came after the United Steelworkers walked out of 11 facilities, including nine refineries accounting for 13 percent of U.S. production capacity, after negotiations on a national contract stalled on Feb. 1. One of the central issues, according to the union, is employee safety.
Torrance has not been involved in the walkouts.
Striking refinery workers said Wednesday's blast underscored concerns the United Steelworkers has about safety standards at refineries and chemical plants nationwide.