Mobil Refinery Explosion Laid to Human Error : Industry: Documents reveal alarm and safety devices were not working on Nov. 24, 1987, and that plant personnel knew it.

Newly obtained information about a devastating blast at Mobil’s Torrance refinery reveals that human error caused an explosion that has triggered two years of legal, political and regulatory battles for the nation’s fifth-largest industrial corporation.

A federal safety report says that in the days before the accident, Mobil failed to follow its own written procedures, which call for alarms to be working during refinery operation. Had those procedures been followed, the federal report says, “the incident would have been avoided.”

Although Mobil long had maintained that “malfunctioning instrumentation” caused the blast, the company conceded that human error was a factor after being questioned about the federal documents by The Times.

Since the accident on Nov. 24, 1987, which caused $17 million in damage and injured 10, Mobil has declined to release details of the explosion and the results of various investigations into the cause of the blast.

The Times obtained Mobil memos and the federal safety report, as well as other documents, months after filing requests with the U.S. Occupational Safety and Health Administration and the city of Torrance under the federal Freedom of Information Act and the California Public Records Act. The documents were gathered as part of the city and OSHA’s investigation into the explosion.

The explosion was triggered by an undetected buildup of hazardous hydrofluoric acid, which is used to boost the octane of unleaded gasoline refined at the plant. The acid overflowed into a tank and mixed with another chemical, causing the blast.

A confidential Mobil memo that is included in the newly available documents says that three alarm systems and monitoring devices designed to warn refinery workers of an unsafe buildup of hydrofluoric acid were not working when the accident occurred. Moreover, Mobil officials knew that the systems were not working. Instead, supervisors at the facility were relying on periodic chemical tests and a separate alarm system to monitor hydrofluoric acid levels. However, what they did not know at the time was that the backup alarm system was not hooked up, the company memo states.

The explosion sent a fireball 1,500 feet into the air, knocked out windows in nearby houses and sent shock waves for miles. Six passers-by and four refinery workers have alleged that they suffered injuries, including broken eardrums, back injuries and, in one case, lung damage from breathing acid fumes.

In the wake of the accident, Mobil spent millions to improve training and plant safety and asserts that the public should not worry about any recurrence.

But trust between the oil company and local officials evaporated after the accident and safety issues raised by the explosion remain an urgent part of the public agenda in Torrance. City officials are vocal in worrying that a similar or worse accident could occur.

Those issues are coming to a head in confrontations involving Mobil, the South Coast Air Quality Management District and Torrance residents, who will vote March 6 on a ballot measure that could force Mobil to spend up to $100 million to restructure its refinery operations. Mobil has said it is prepared to spend more than $500,000 to defeat the measure.

Refinery manager Wyman Robb, saying in a recent interview that the accident “is old stuff” not worth dredging up, declined to answer questions about the role that human error played in the explosion.

“If we have to deal with it in court, we have to deal with it in court. I don’t think we necessarily have to deal with it . . . with the public right now.”

Reading from a prepared statement, he added: “Any allegation that Mobil knew that the (unit that exploded) was unsafe and went ahead to operate it is absurd. Safety is, and has been, our top priority.”

“Obviously mistakes were made, such as equipment failure and human error,” said Mobil spokesman Jim Carbonetti in a separate recent statement. “We have learned from these mistakes and have invested millions of dollars to improve our operations to make certain it does not happen again.”

Despite Mobil’s assurances, the new information about the central role of human error in the accident is already providing ammunition to those arguing that hydrogen fluoride--which in its liquid form is hydrofluoric acid--should be banned from the Mobil facility and from three other refineries in Los Angeles County. They argue that the plants should be converted to use sulfuric acid instead.

Torrance Mayor Katy Geissert said the new information strengthens her resolve to pursue a city lawsuit filed against Mobil last April that seeks increased regulatory power over the refinery. The documents, she said, show “strong evidence” that “the potential for human error is so great that the further use of hydrofluoric acid” may no longer be acceptable at the refinery.

“You eliminate hydrofluoric acid at the Mobil refinery and you eliminate the possibility of stupid acts and honest mistakes killing our residents,” said Councilman Dan Walker, sponsor of the March 6 ballot measure.

Hydrofluoric acid, which is more toxic than hydrogen cyanide gas, has the potential of forming a lethal, ground-hugging cloud. The explosion and fire released an estimated 12 gallons of hydrofluoric acid.

In addition to local concern, the Southern California Air Quality Management District staff has pending a recommendation that the bulk use of hydrofluoric acid at the four refineries be banned.

Mobil, whose Torrance refinery produces 12% of all gasoline consumed in Southern California, says that it would cost $100 million to convert to sulfuric acid.

The unit that exploded performs alkylation, a process discovered in the 1930s that uses hydrofluoric acid as a catalyst to combine petroleum gases to produce high-octane unleaded gasoline.

The explosion took place some distance from the main part of the alkylation unit and the blast did not rupture any of the tanks containing large amounts of hydrofluoric acid. Mobil typically has about 29,000 gallons of the substance on hand. It is used only for the alkylation process, with the bulk of it circulating through the unit, rather than staying in storage.

The tank that exploded is part of a four-stage section whose job is to separate acid from propane, a by-product of the alkylation reaction.

That is done first by gravity; the acid is heavier than propane and mixes poorly with it. The acid settles in a barrel-like “boot” about the size of a 55-gallon drum.

The explosion occurred when the acid overflowed the boot and into a tank, known as the KOH treater, which was filled with either sodium hydroxide or potassium hydroxide. It has not been disclosed which of the two chemicals was in the KOH treater, although they are equally hazardous when mixed with hydrofluoric acid.

A trail of trouble led up to the explosion.

Ten days before the explosion, there were problems with the acid level in the boot and the instruments that measure it, according to a Mobil memo.

Four days before the explosion, the KOH treater overheated seriously, according to an OSHA report.

According to a transcript of an interview with Torrance investigators, Mobil instrument technician Steve Bowling said: “The paint was peeling off (the KOH treater). . . . They knew that something was not right. . . . There’s not supposed to be heat there at all.”

Mobil found out that the drain valve in the acid boot “had been blocked inappropriately, allowing some acid to reach the KOH treater,” said a memo by refinery manager Robb. He wrote without elaboration that “corrective follow-up was taken.” The memo does not say whether the alarms were working at that time.

The day before the explosion, a Mobil memo said that the acid boot alarms were still out of order and told operators to check the acid boot levels twice a shift. The memo emphasized that it would be safer to bypass the KOH treater “if you have any doubts about where the acid level is.”

The memo ended: “Work safely.”

The day of the accident, Mobil put the KOH treater on line at 2:30 a.m.

A number of things were unusual. Three devices that could signal or prevent an accident were not working in the acid-removal system.

The automatic level controller for hydrofluoric acid in the boot--which works on the same principle as the float in a household toilet--”did not appear to be working,” said a Robb memo. Alarms connected to the controller also were not working properly. Operators “were controlling the level of hydrofluoric acid manually,” he wrote.

In addition, Robb wrote that an instrument used to check the acid visually--called a sight glass--was “inoperable.”

A Mobil work order for instrument technicians that day says that the automatic level controller and the acid level alarms connected to it needed repair.

In response to that work order, Bowling, a 5 1/2-year veteran at Mobil, checked the system about 10 a.m. He couldn’t fix the alarms and told that to the unit operators.

In the interview, Torrance Police Detective Gary Hilton twice asked Bowling about Mobil’s apparent lack of response to learning he was unable to fix the alarms:

“If you told them at 10 in the morning, why didn’t they do something about it?” Hilton asked.

“Well, I don’t know why, . . .” Bowling said.

In addition to the decision to restart the alkylation unit with three alarm and safety devices not working, Mobil also decided not to run the acid through an intermediary treatment station called the alumina tower.

Had the acid been run through the alumina tower, the overflow of acid might have been detected before it reached the explosive contents of the KOH treater because the tower has its own set of alarms. OSHA and the Torrance Fire Department criticized Mobil for bypassing the tower.

The reasons Mobil bypassed the tower have never been explained publicly.

With the sight glass inoperable, the automatic acid-level controller shut off, its high- and low-level alarms known to be malfunctioning and the alumina tower bypassed, all that Mobil had to warn of a potential explosion was periodic chemical sampling and one last set of acid-level alarms, according to a Robb memo and other documents.

The last chemical test was done 1 1/2 hours before the explosion and Robb’s memo says it detected no problems.

The alarms had been tested and Mobil believed they were working, Robb wrote later.

But Mobil found out after the explosion that the alarm system was not connected to the acid boot, Robb’s memo said.

No one has explained why Mobil’s test failed to disclose that the alarms were not connected.

However, OSHA Regional Administrator Frank Strasheim in a recent interview criticized Mobil’s test as “not valid” because it did not tell the difference between a device that was hooked up and one that was not. John Hermanson, a former OSHA district director who released documents to The Times, said Mobil was “dumb” not to ensure that the alarm was working when other safety devices were known to be out of order.

Despite Mobil’s assertions that employees believed the alarm system was working when they decided to proceed, an OSHA investigative report says that a signal light in the refinery control room should have alerted Mobil that the alarm was not working properly.

At 5:53 p.m., the KOH treater blew up.

It started a raging fire visible for miles. The blast destroyed a water gun at the alkylation unit that could have been used to fight the fire or drench acid fumes. Flaming debris fell across Crenshaw Boulevard. A quarter-mile away, the shock wave blew out windows in 21 homes.

Mobil, which had a contractor working on the water line to the alkylation unit, “did not have water for 20 minutes,” said OSHA, which criticized the oil company for failing to put down emergency hose lines.

Employees ran in--some without safety suits--to turn off valves. That sealed the section from its supply of acid and stemmed the flow of flammables to the fire, which burned itself out the next morning.

Six months later, OSHA issued five citations for serious violations of federal safety regulations. A serious violation is a hazard with a substantial probability of causing death or serious injury and which the employer knew about or should have known about.

The five citations said that Mobil should have had its alarms and controller working, that its operating procedures were inadequate, that relief valves on the KOH treater were the wrong size, that firefighting equipment had been inadequate, and that employees trying to close valves after the explosion should have worn protective suits.

Mobil did not dispute four of the citations and paid a $4,000 fine. OSHA dropped the fifth citation last April, after Mobil successfully argued that no relief valve could have prevented the explosion.

In rebuilding the alkylation unit, Mobil rewired the existing alarms on the acid boot for more reliability and added another acid-level alarm. Procedures now require operators to check the instrument readings against the sight glass. Mobil also installed an automatic shunt system, in case of another acid overflow, to keep acid-laden propane away from the KOH treater. The oil company plans to install an underground tank protected against explosion to dump large amounts of hydrofluoric acid in the event of another emergency.

Since the accident, the refinery also has improved training; last year it installed a computer-assisted learning program specially tailored to the Torrance alkylation unit.

One of the scenarios includes an overflow from the acid boot.

ANATOMY OF MOBIL REFINERY BLAST

The alkylation unit--where the explosion took place--comes after crude oil has been distilled, purified of contaminants and “cracked” into lighter components. Using hazardous hydrofluoric acid as a catalyst, the alkylation process combines hydrocarbons to volatile to use in gasoline to form a high-octane gasoline component. Two byproducts--isobutane and propane--are reclaimed and used elsewhere in the refinery; the hydrofluoric acid is recycled. The explosion took place where propane is separated from hydrofluoric acid.

The explosion occurred away from the main part of the alkylation unit--where most of the hydrofluoric acid is stored and used. It blew apart a tank in a four-stage unit that removes the acid from propane.

Most of the acid is first separated from the propane by gravity. The acid collects in a barrel-like “boot,” (1) which hangs below a larger horizontal storage tank.

Acid from the boot is drained for reuse, while partially cleansed propane goes on the the second stage, a distillation process (2) that removes most of the remaining acid.

A chemical process using aluminum oxide further purifies propane in the third state--the alumina tower(3).

The final stage removes what is supposed to be only trace amounts of acid in a steel tank, known as the KOH treater (4), filled with highly reactive sodium hydroxide or potassium hydroxide.

WHAT WENT WRONG Acid overflowed the boot unnoticed and reached the KOH treater, which detonated like a bomb.

WHY IT HAPPENED A. Sight glass on acid boot inoperable. B. Automatic controller on acid boot was not working; alarms connected to controller were not working. C. Mobil fails to hook up remaining alarm system on acid boot; relies on false readings from unconnected alarm. D. Alumina tower and its alarms had been bypassed.

SOURCES: Mobil, OSHA, Torrance Fire Department