Two days before Thanksgiving, a thunderous explosion shook Mobil Oil Corp.'s refinery in Torrance, sending refinery workers running for cover and igniting a spectacular fire that burned for two days.
Furious flames fueled by a rich mixture of propane and butane soared into the night sky, snarling traffic on major streets and the nearby San Diego freeway.
The blast, which was heard for miles around, shattered windows in nearby homes and businesses, stained cars with a petroleum residue and caused millions of dollars in damage to the refinery. Mobil has received at least 250 property damage claims from neighbors, but only four people at the refinery suffered minor injuries.
Mobil has apologized for any inconvenience the explosion may have caused and has sought to reassure the community that safety is its highest priority.
But the Nov. 24 explosion has rekindled a debate about whether a major refinery processing millions of gallons of gasoline, diesel, jet and other fuels daily can operate safely in a densely populated urban area.
Members of the Torrance City Council want that question answered.
It is the same question that was asked in December, 1979, after an explosion and fire at Mobil killed two refinery workers and a passing motorist when her car ignited a vapor cloud that had drifted from the tank farm at Van Ness Avenue and Del Amo Boulevard.
"They are a major landowner right in the center of our city," Torrance Mayor Katy Geissert, said last week. "We certainly have a responsibility to the public to do whatever is within our authority to ensure a safe operation."
The concerns about safety grew when Mobil announced late Friday that the explosion was caused by too much lethal hydrofluoric acid in a refinery unit.
"It certainly heightens our concern about how the hydrofluoric acid is being used, controlled and contained," Geissert said.
After investigating, Mobil found that the explosion and fire started in a propane treater in part of the refinery called an alkylation unit.
The 30-foot-tall alkylation unit removes water and other impurities from fuels while producing gasoline, propane and butane. The propane treater is designed to remove small amounts of acid from liquid propane.
Mobil blamed the excess acid in the propane treater on "malfunctioning instrumentation" in the alkylation unit. The resulting reaction "created abnormal pressure" in the propane treater vessel, "causing it to rupture," the company said. Pieces of the exploding vessel then severed nearby pipelines, fueling the fire.
"The hydrofluoric acid never escaped off the property," said Thomas Gregory, the refinery's manager of safety and training. "There was no danger to the public."
The Environmental Policy Institute in Washington reported earlier this month that 58 U.S. oil refineries, including Mobil and two others in the Los Angeles area, use hydrofluoric acid.
The environmental group warned that a major accident that released hydrofluoric acid could pose as serious a danger as the methyl isocyanate leak at a Union Carbide plant in Bhopal, India, that killed more than 2,000 people in December, 1984.
The group said tests conducted last year in the Nevada desert for the oil industry by the Lawrence Livermore National Laboratories show that a 1,000-gallon release of hydrofluoric acid could "produce a toxic gas cloud lethal to all human beings exposed within a range of five miles from its release point."
The nonprofit organization said hydrofluoric acid forms a dense cloud that hugs the ground and moves with the wind away from the accident site.
In October, more than 60 people were injured and 3,000 residents were evacuated in Texas City, Tex., when a hydrofluoric acid leak at a Marathon Oil Co. refinery sent a vapor cloud over the city.
Nearly 500,000 people live within five miles of the Mobil refinery.
Mobil refinery manager Wyman D. Robb said the environmental group "largely overstated" the risk involved. Robb said Mobil workers are trained in the handling of the chemical and any emergency that might arise.
About 250,000 pounds of the acid is now stored in vessels at the Torrance refinery, down from a peak of 450,000 pounds, according to Mobil.
Robb said the acid is used at the refinery as a catalyst to boost the octane in gasoline. "We have been using this process at the Torrance refinery for over 40 years," Robb said. "We have never had a serious incident where the acid has been emitted into the community."
"We have an awful lot of respect for it," Robb said. "We have designed and built our process units with the utmost of safety."
In addition, the company has pledged to install backup instrumentation before the damaged refinery unit is placed back in service.