When walls start shaking and dishes rattle ominously, Clifford Heise hurries outside his Torrance home to stare at the southern sky.

“If it’s red, you know it’s Mobil,” he says, “and you think, ‘Quick, which way is the wind blowing?’ ”

For hundreds who live near the mammoth Mobil Oil Corp. refinery in Torrance, the fear of earthquakes is overshadowed by a fear of toxic clouds. In their imaginings of hell, a blast somehow unleashes a deadly poison that wafts over the refinery fence and straight into their homes, scorching their skin, searing their lungs.

Nearly six years ago, spurred on by such fears and a spate of accidents, Torrance’s normally mild-mannered city government sued Mobil in an effort to declare the refinery a public nuisance. The result: a widely praised 1990 court-approved agreement in which Mobil promised to either stop using highly toxic hydrofluoric acid or craft a safe version. The story had a David-and-Goliath flavor, as a quiet Los Angeles suburb appeared to wrest a major concession from the nation’s sixth-largest industrial corporation.

Today, however, some in Torrance are wondering who really won.

Jolted by a fiery Oct. 19 explosion at Mobil that sent 28 injured workers to area hospitals, some residents have grown cynical that anything — whether legal pacts or citizen outcry — will make the refinery safe enough.

Even so, the City Council appears poised to accept Mobil’s plan to switch to a modified form of “HF,” rather than phasing it out altogether. That possibility is viewed with dismay by some who fear that the acid could wreak a Bhopal-type disaster in the South Bay.

*

The council vote, which could come at Tuesday’s meeting, is the toughest test yet of a legal agreement that had been heralded nationally as a model of public-private cooperation.

Some residents fret about a maze of secrecy agreements between Mobil and the city. Some simply want straight answers.

A recent Mobil presentation, Heise complains, was “so clouded with technical jargon that no one could figure out what they were talking about.”

Images of clouds proliferate in the drama now playing out in Torrance: deadly acid clouds, exploding butane clouds, steam swirling daily above Mobil’s towers, suspicions that legal pacts and technical studies are clouding the truth about what goes on behind the refinery’s gracefully landscaped borders.

Mobil officials promise that their modified HF and other techniques will reduce by 80% the chance that a toxic cloud could threaten refinery neighbors. They praise its development as a $20-million technological breakthrough.

“We believe this new alkylation process takes us a major step closer to our goal of becoming the safest refinery in the world,” Mobil wrote in a recent letter sent to 43,000 Torrance households.

The stakes are high for Mobil. If it were forced to drop HF for the industry’s alternative, sulfuric acid, it would have to spend as much as $100 million to retool the refinery, company officials say.

*

A turning point in the controversy came last month when both a court-supervised safety adviser and Torrance’s fire chief came out in favor of Mobil’s modified HF. The new technology “represents a significant reduction in risk to both on-site and off-site populations,” Fire Chief R. Scott Adams wrote in a report to the council.

Some residents remain wary, citing an array of concerns:

* Under a court-monitored deadline, Torrance must decide by Feb. 16 whether to object to the use of modified HF. That means the City Council could vote before the state’s workplace safety agency, Cal/OSHA, completes its report on the recent explosion, expected in mid-February.

(Cal/OSHA reassigned its primary criminal investigator on the Mobil case last month. The action came after Mobil complained about a local newspaper story quoting the investigator expressing concern about the potential for an HF release in the explosion. The investigator has since been unavailable for comment. Cal/OSHA reassigns investigators to avoid jeopardizing an investigation if employers question their conduct, a Cal/OSHA spokesman said.)

* The 1990 pact required Mobil to eliminate HF unless it no longer formed “an aerosol or dense vapor cloud upon release.” Although the modified version no longer forms an aerosol, Mobil has been unable to show that it would not form a dense vapor cloud, according to a report from the safety adviser, EQE Engineering of Irvine.

Even so, the modified version does meet revised rules that permit Mobil’s use of HF as long as it is shown to pose no greater risk than sulfuric acid, according to EQE. The revisions were approved by the City Council in September behind closed doors.

* Mobil has not made public its study comparing the risks of modified HF with those of sulfuric acid, calling it proprietary. That study was used by the safety adviser to prepare its recommendation.

* Although Mobil researchers have announced the discovery of an additive that they say can reduce HF’s dangerous, cloud-forming tendencies, Mobil has not publicly disclosed the identity of the additive, citing competitive concerns. The identity is known to the safety adviser and some city officials, who are bound by confidentiality agreements with Mobil.

In an attempt to assuage the public’s fears, researchers from Mobil’s laboratory in Paulsboro, N.J., tried to explain their work at a meeting last month.

*

Mobil showed film footage of white puffs of airborne hydrofluoric acid billowing at an industry test site in Oklahoma. Traditional HF produced a large balloon-like cloud, while the acid mixed with the new additive created a mist that was visibly smaller and more transparent.

Yet researchers’ attempts to explain the technology — in language laden with dense scientific terms — simply riled the crowd. “It’s like, they just don’t get it, how serious this is,” Councilman George Nakano said.

The residents’ frustration shows that the Mobil pact has effectively taken the HF decision out of citizens’ hands, said Carlos Porras, Southern California director of Citizens for a Better Environment.

But Michael Leslie, an attorney representing the city, defends the Torrance-Mobil pact as a clear-cut success. Without it, he said, “we wouldn’t be addressing any of these issues. The city would have no real input into practices at the refinery.”

The debate has special resonance in a county that clings to the notion of clean air and clean industry while consuming colossal amounts of gasoline from this very refinery.

Some critics question whether a massive oil refinery can operate safely alongside homes and playgrounds in Torrance, a sedate, middle-class suburb of 135,000 people 20 miles southwest of Downtown Los Angeles.

Refinery manager Joel Maness insists that it can.

“The thought that any industrial facility has to be located out in the middle of the desert, with nothing but jack rabbits within a hundred-mile radius, is absurd,” Maness said.

Mobil sprawls across northern Torrance, 750 acres of industrial spires, steaming pipes and tanks visible from freeways miles away, the source of 16% of the gasoline consumed in Southern California.

The refinery opened in 1929 amid bean and strawberry fields but was soon surrounded by tidy stucco houses whose occupants seemed largely unconcerned about petrochemical safety. After all, Torrance takes pride in a peaceable mix of homes and industry, its slogan boasting, “A Balanced City: Industrial, Residential, Commercial.”

*

The peace ruptured one winter evening in 1979, when a butane cloud escaped from Mobil and wafted toward a passing car. The car apparently ignited the cloud, setting off a huge fire that killed the driver and two workers.

Then, in 1987, an explosion caused a 17-hour fire, injured six workers and led to a small HF release that did not leave the refinery grounds. Public alarm over toxic clouds grew, especially because a massive HF release in Texas weeks earlier had sent more than 1,000 people to hospitals with skin, nose, eye and lung irritations.

A 1990 citizens ballot initiative seeking to end Mobil’s use of HF lost at the polls. But that same year City Hall and Mobil resolved the city’s public nuisance lawsuit with a court-approved consent decree, hailed in both industry and environmental circles as a landmark.

The decree established a court-supervised safety adviser, a consulting firm that will monitor the refinery through 1997. It also required Mobil to stop using HF by 1997 unless a safe form was approved by the safety adviser by the end of 1994.

Meanwhile, Maness arrived in mid-1990 to head up refinery operations. A Texas native with a soft-spoken drawl and a ready smile, he has worked hard to defuse tensions between Mobil and its neighbors. He talks proudly of millions of dollars invested in recent safety improvements, of community open houses and other programs “putting a face on the refinery.”

His efforts have won praise from city officials, especially when years passed without a major accident at Mobil.

Mobil now mails a regular newsletter to residents, reporting on items such as the $50,000 contributed by Mobil to the Torrance Parks and Recreation Department, the $300,000 gift to Torrance Memorial Medical Center, free CPR training, scholarships for Torrance students and the Mobil St. Patrick’s Day Run for the Blind.

*

The days of city-Mobil feuding seemed like ancient history. Then, on Oct. 19, flammable gases spewed from a pipeline that apparently had been left disconnected, exploding close to the unit where HF is used. Abruptly, residents began paying close attention to Torrance-Mobil relations.

The immediate question is whether Mobil will continue using HF.

The chemical stirred widespread concern after 1986 industry tests found that a 1,000-gallon HF release could generate a dense, ground-hugging cloud potentially lethal as far as five miles downwind. The Torrance refinery, which uses the acid to boost the octane of unleaded gasoline, stores 29,000 gallons on-site.

Since 1979, HF has been involved in eight of 65 Mobil incidents listed in a Torrance Fire Department report given to the council. But only two known incidents involved measurable amounts of HF, according to a Mobil safety official: 165 pounds released in the 1987 explosion and 32 pounds released in a 1992 mechanical failure. No acid wafted off-site, Mobil and city officials say.

“There is not one documented incident in which HF has extended beyond the fence line,” said Battalion Chief Kennith Hall, the Fire Department’s hazardous materials chief.

While engineers, lawyers and politicians work toward a truce in this “balanced city,” some are devising a more down-to-earth defense against toxic clouds.

*

An emergency drill called “Shelter in Place” was launched last fall in the 22,000-student Torrance Unified School District, a response to potential accidents at Mobil, other plants or the railroad tracks traversing the city.

When a special bell rings, students take shelter inside classrooms where teachers place duct tape around windows and stuff wet towels under doors — just in case a chemical cloud comes their way.