Orange County fire officials said on Monday that the threat of a major explosion from an unstable tank of toxic chemical was eliminated, but that the danger of a smaller-scale explosion remained.
“The crisis is not averted,” TJ McGovern, the interim fire chief for the Orange County Fire Authority, said at a news conference on Monday. “Let me be clear. Evacuation zones are still in place. The threat is not eliminated.”
In an interview with the TV station KTLA, Mr. McGovern said that the tank could still leak or explode, though not to the extent they first feared.
That threat, he said, means that evacuation orders were still in place for more than 40,000 residents who live near the industrial site in Garden Grove, Calif., as local authorities assessed whether it was safe for residents to return home.
The statements on Monday came after the authorities said that a crack had continued to relieve pressure in the tank, dropping temperatures inside.
On Sunday night, the authorities said, firefighters — who have been hosing down the 22-year-old tank for days in an attempt to cool it — removed insulation to hasten their progress.
“The trajectory is headed in the right direction for the first time since Thursday,” Thomas J. Umberg, a state senator who represents the area that has been evacuated, said on Monday.
“The challenge now is that people want to get back in their homes,” he said, adding, “and they can’t go back until it’s safe.”
On Monday, Gov. Gavin Newsom announced that the state had secured a presidential emergency declaration from the Trump administration, which could help displaced people and businesses that closed.
Firefighters responded on Thursday to an industrial site, belonging to GKN Aerospace, where a tank containing about 7,000 gallons of the chemical methyl methacrylate was becoming pressurized and releasing gas as the tank overheated.
According to the Environmental Protection Agency, exposure to methyl methacrylate can irritate the eyes and skin and make it difficult to breathe, among other symptoms. Birth defects have appeared in exposed animals.
Local authorities issued evacuation orders to thousands on Friday, as the tank’s temperature increased and the tank bulged, a sign that it could potentially explode. On Sunday, officials said they found that the tank had cracked, relieving some of the internal pressure. Internal temperatures also dropped from 100 degrees to 93 degrees, possibly solidifying some of the liquid inside.
“The crack is there,” Craig Covey, an incident commander with the fire authority, said on Monday. “We have verified that it’s there, and the tank has released its pressure.”
Mr. McGovern said at a later news conference on Monday that local officials were unsure when it would be safe for residents to return because it was unclear how much liquid in the tank may have solidified.
The Orange County District Attorney’s Office said on Monday that it was investigating GKN, a British manufacturing company that produces jet engine parts, landing gear and other components for military and civilian aircraft.
Christina Morales is a national reporter for The Times.
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