The chemical industry has been well aware of the risks of the type of thermal runaway reaction that forced 50,000 people from their homes in Orange County last weekend, reviving years of warnings from researchers about the potential dangers.
Nearly 15% of incidents in the U.S. involving uncontrolled chemical reactions between 1980 to 2001 were thermal runaway incidents that involved rapid polymerization of a chemical, according to a study published in the journal ACS Omega, citing information from the U.S. Chemical Safety and Hazard Investigation Board.
Such incidents have led to deaths globally, but some experts say the industry has struggled to improve safety.
In Orange County, the crisis was sparked by thousands of gallons of a highly toxic chemical in a failing pressurized chemical tank that was heating up at a Garden Grove aerospace firm. There was a potential of fire or flash fire over many city blocks, and there were businesses, dozens of homes and an elementary school in a potential damage blast zone.
The worst-case scenario was averted over the Memorial Day weekend. But serious questions remain over how such a near-disaster could have happened.
Authorities suspect that the cooling system responsible for maintaining the temperature of a tank filled with a hazardous chemical at GKN Aerospace failed, leading to the crisis at the facility that triggered evacuations, Orange County Fire Authority Interim Chief TJ McGovern said Tuesday.
This likely led to a buildup of heat in the pressurized tank filled with 7,000 gallons of a highly reactive liquid chemical called methyl methacrylate, or MMA, which can be used to make items such as Plexiglass as well as household goods.
“We don’t know why, but it stopped cooling,” McGovern said Tuesday. “So that’s what started this event, to where the product heated up and it off-gassed through the relief valve, and that’s how this whole response started. We’re just now being able to get to the tanks, so there’s definitely more to come of what caused it.”
Fire officials and experts were faced with a seemingly no-win situation: a “boiling liquid expanding vapor explosion,” or BLEVE, which would have caused widespread damage and released toxic material into the air, or a potential chemical spill that could have fouled up waterways and the ocean. Inhaling MMA can irritate the lungs and, at high levels of exposure, can cause severe respiratory distress and hospitalization; long-term exposure has been linked to serious organ damage.
Although fire officials referenced the off-gassing of “fumes” and said on Friday that the tank was “no longer purging any kind of product,” the county’s health officer, Dr. Regina Chinsio-Kwong, on Monday said no fumes or vapors were issued during the incident. The U.S. Environmental Protection Agency said its air monitors had not detected toxic airborne chemicals, but environmental experts were skeptical that no toxic substances had been released.
The suspected failure of a cooling system, and the introduction of heat to a pressurized tank with MMA, planted the seeds of a potential catastrophe.
When liquid MMA is exposed to heat or light, it will start a chain reaction, said Elaine Villanueva Bernal, a lecturer at Cal State Long Beach’s department of chemistry and biochemistry.
As MMA solidifies, “it produces heat, and then in producing that heat, it furthers the chain reaction, so it keeps going and going and going,” Bernal said.
If it gets out of control, this leads to a process called a thermal runaway.
MMA is a highly reactive chemical, a monomer that can be used to make polymers of hard, durable, lightweight and transparent plastics. But introducing heat to MMA in a pressurized tank caused the chemical to react, starting its transformation from a liquid to solid state, which produces even more heat.
Eventually, it can result in a BLEVE.
That refers to when a liquid is “rapidly depressurized, causing a nearly instantaneous transition from liquid to vapor with a corresponding energy release,” and is “often accompanied by a large aerosol fireball,” according to the American Institute of Chemical Engineers’ Center for Chemical Process Safety.
GKN Aerospace, based in Britain, makes landing gears, jet engines and other materials for commercial and military aircraft at its Garden Grove facility. The company did not respond to questions Tuesday, but earlier said that “we apologize for the ongoing disruption this incident is causing and our priority remains its safe resolution.”
Orange County ended up in a much better position than incidents elsewhere. In India, 12 people died and more than 580 were injured after a thermal runaway of styrene and release of styrene vapor occurred at the LG Polymers plant in the port city of Visakhapatnam in 2020. A committee appointed by India’s top environmental court blamed “gross human failure” and a lack of basic safety norms for the disaster, the Associated Press reported.
“Lessons have not been learned,” the ACS Omega study said, referring specifically to styrene-related runaway incidents.
And in 2012, one person died and 36 were injured in an explosion and chemical fire at a chemical plant in Himeji, Japan. The disaster occurred after the “runaway polymerization of acrylic acid” in an intermediate storage tank, a study published in the journal Process Safety and Environmental Protection said, citing information from the factory’s operator, Nippon Shokubai Co.
A study published in 2023 urged more attention to be paid to MMA.
“The correct choice of operating conditions often constitutes the first line of defense against thermal runaway events,” the study, published in the journal Thermochimica Acta, said. Without evaluating potential thermal hazards, implementing safe process designs and strengthening thermal safety, “the highly exothermic nature of the reaction may pose a severe threat to process safety as well as to industrial-scale equipment and to human lives.”
The report from the U.S. Chemical Safety and Hazard Investigation Board, issued in 2002, called on a need to “improve the management of reactive hazards” following two accidents in the 1990s in New Jersey, one of which killed five workers.
“Reactive incidents are a significant chemical safety problem,” the report concluded.
In the case of the Orange County chemical tank, officials watched as the temperature gauge in the crippled tank rose from 77 degrees Fahrenheit on Friday, to 90 degrees on Saturday, to at least 100 degrees on Sunday — the maximum reading on the gauge. At one point, the tank began to bulge.
The easiest solution — pumping in a neutralizing agent to stop the reaction — failed because, presumably, the MMA in the valve had reacted and transformed from a liquid to a solid and clogged up the valve, meaning the neutralizing agent could not be pumped in, nor could the toxic reactive fluid be drained out, according to Elias Picazo, an assistant professor of chemistry at USC.
Crews could not “get anything into the compromised tank because, the theory is, the product was starting to solidify and it gummed up the dump valves,” McGovern said.
All officials could do was spray cool water on the tank, hoping that by cooling it down, tragedy could be avoided. On Monday, Craig Covey, an Orange County Fire Authority division chief, said firefighters wanted the MMA chemical to stabilize and become more like gel — rather than the flammable liquid they were first dealing with. “You have to control that temperature to get that egg done right‚ and not crack the shell,” Covey said.
In the end, though, neither an explosion nor a giant spill of fluid that could foul up waterways and the ocean occurred. The cooling strategy appeared to have worked.
On Monday, “we really turned the corner,” McGovern said. Officials confirmed there was a crack in the tank and it was no longer pressurized, taking the concern of a BLEVE “off the table,” he said.
Officials then reduced the evacuation zone.
The crack “allowed us to get more of our crews into the tank,” he said. “They were able to start peeling back the external wall of the tank and move the insulation.”
Then they were able to focus their unstaffed hose lines more on the internal tank to start better cooling measures and reduce the internal temperature of the substance. As of Tuesday morning, the substance was hovering between 90 and 92 degrees Fahrenheit and water was still flowing on it.
Later Tuesday, crews started shutting down some of the water supply that’s cooling the tank. Crews were going to start with one of the two water systems and see how the temperature responds.
“We’re looking for any fluctuations. What we do not want is the internal temperature to increase because we’re shutting down the water. We would really like it to decrease, but as long as it doesn’t move, we’re looking at the stability of the internal temperature.”
If the temperature remains constant, they’re going to consider shutting down the secondary water supply. After that, if the temperature doesn’t fluctuate, it would “tell us that the fire problem, or the small explosion, has been mitigated,” McGovern said.
By Tuesday night, all remaining evacuation orders were lifted, with authorities declaring there was no remaining danger of an explosion, chemical leak or fire.
Times staff writers Tony Briscoe, Clara Harter and Meg James contributed to this report.
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