The crisis at a Garden Grove aerospace firm that required the evacuation of 50,000 people was probably caused by the failure of a cooling system designed to regulate the temperature of chemical tanks, interim Orange County Fire Authority Chief TJ McGovern told The Times on Tuesday.
This may have led to a buildup of heat in a pressurized tank filled with 7,000 gallons of a chemical called methyl methacrylate, a highly flammable liquid monomer used to manufacture plastics.
“We don’t know why, but it stopped cooling,” McGovern said. “So that’s what started this event, to where the product heated up … 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.”
Officials evacuated an estimated 50,000 people on Friday after determining one of the three tanks at the aerospace company was in danger of a massive blast called a boiling liquid expanding vapor explosion, which would have caused widespread damage.
Further evaluations over the Memorial Day weekend found the tank had a crack that had reduced pressure, eliminating the possibility of a catastrophic blast.
“Yesterday we really turned a corner,” McGovern said.
The confirmation that the tank was no longer pressurized enabled members of a team — made up of experts from the Fire Authority, Los Angeles and Long Beach fire departments, Los Angeles County and San Bernardino County fire departments, and the California Office of Emergency Services — to get closer to the tank to peel back the external wall and insulation, McGovern said.
This enabled them to focus their unstaffed hose lines on the internal tank to cool the chemical more effectively, dropping the temperature to around 92 degrees.
Although authorities reduced the size of the evacuation zone on Monday, officials stressed that the danger was not over in the immediate area around the Garden Grove aerospace facility. About 16,000 people remain under mandatory evacuation orders in the blocks immediately around the property.
“We want to get you home as soon as possible, and our goal is to do that as soon as it’s safe to do so,” Greg Barta, a spokesperson with the Fire Authority, said during an incident update Tuesday morning.
Officials have also emphasized that the crisis did not result in the release of chemicals that could be harmful.
“I want to reassure everyone who is outside of the new evacuation zone that, when you go home, you can feel safe,” said Orange County Health Officer Dr. Regina Chinsio-Kwong. “There was no contamination, there were no fumes, there were no vapors that came from this incident. There was no leak.”
On Tuesday, McGovern said officials are going to start shutting down one of the two water supplies that are cooling the tank and assess how it 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. … We’re looking at the stability of the internal temperature,” he said.
If the temperature remains constant, officials will 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,” he said.
By Tuesday night, officials probably will have a better picture of next steps, he said, including further reducing the size of the evacuation zones.
“We’re not there yet, but we’re getting there,” McGovern said.