The worst threats from a damaged chemical tank in Southern California have passed, with authorities saying a major explosion was no longer imminent, but evacuations are still in place amid continued risks on May 26.

The damaged tank prompted tens of thousands of evacuations near Garden Grove, California, in Orange County, south of Los Angeles, starting on May 21. The tank, which stores a toxic industrial chemical, overheated and caused pressure to build up.

Officials have previously said the crisis would lead to a catastrophic explosion or a spill of the roughly 7,000 gallons of methyl methacrylate at the GKN Aerospace manufacturing facility.

By May 25, they were more optimistic.

“The most catastrophic and worst-case scenario was mitigated and resolved,” said TJ McGovern, interim chief of the Orange County Fire Authority, in a news conference the evening of May 25.

The potential for the most serious crisis was averted after officials discovered a crack in the tank, which relieved significant pressure and the likelihood of a BLEVE, or a “boiling liquid expanding vapor explosion.” The evacuation zone was reduced on May 25, but still covered about 16,000 residents, the fire authority said.

“Residents have been displaced from their homes, businesses have been impacted, and I am relieved that many of you will be able to return home,” Garden Grove Mayor Stephanie Klopfenstein said. “Garden Grove will get through this together.”

President Donald Trump, on May 25, signed an emergency declaration at the federal level.

Thousands of residents can go back home after explosion risk mitigated

A damaged chemical tank in southern California cracked over the weekend, which authorities were hopeful would relieve pressure and reduce the risk of an explosion.

Some 50,000 residents in Garden Grove, a city of roughly 170,000 about 40 miles (60km) south of downtown Los Angeles, have been evacuated and are waiting for a resolution.

The tank overheated on Thursday and began venting vapors, leaving local and state officials scrambling to evade a worst possible scenario at the aerospace company site.

No injuries have been yet reported.

Fire officials planned to send in a team overnight to determine if the pressure has been relieved, which would reduce the worst-case scenario of an explosion, TJ McGovern, the Orange county fire authority interim chief, said in a video posted late on Sunday to the agency’s X account.

Atmospheric modeling showed an active leak from the tank as of Sunday night, McGovern said.

Firefighters have repeatedly sprayed the tank with water in an attempt to cool the chemical inside, methyl methacrylate, which is used to make plastic parts. The tank’s interior reached 100 degrees (37.7 Celsius) on Sunday, an increase of 10 degrees Fahrenheit (5.5 Celsius) since Saturday.

Fire officials over the weekend discovered the tank had cracked, lowering the potential for a devastating blast.

The tank at GKN Aerospace Transparency Systems, which makes parts for commercial and military aircraft, holds 6,000 to 7,000 gallons (22,700 to 26,500 liters) of methyl methacrylate used to make plastic parts.

Monitoring tests found air pollution around the evacuation zone was within normal limits and specialized equipment is being used to ensure gas is not released, state and federal environmental officials said Saturday.

The first goal of firefighters is to cool off the chemical inside the tank to prevent a leak or explosion.

Drones were monitoring temperatures at 10-minute intervals to watch for any spikes. Containment barriers have been set up to prevent the chemical from getting into storm drains or reaching creeks or the nearby ocean in the event of a spill, the Orange county fire authority division chief, Craig Covey, said on social media.

As the interior temperature rises, methyl methacrylate converts from a liquid to a gas and increases the pressure, according to Andrew Whelton, a Purdue University engineering professor who said the crack could mean product or pressure is being released, reducing the chance of explosion.

“Think of a soda can. If you leave it in a hot car it can explode,” Whelton said. “But if you put a hole in the can, the product is released and the can itself doesn’t explode.”

Aerial photos taken by the Associated Press showed streets in the area were empty on Sunday, while several evacuation shelters were open. At a high school in neighboring La Palma, people slept in cars or on mats and sleeping bags on the asphalt.

Garden Grove is next to Anaheim, home to Disneyland’s two theme parks, which were not under evacuation orders. Park officials said they were monitoring the situation.

Exposure to methyl methacrylate can cause serious respiratory problems, neurological problems and irritation to the skin, eyes and throat, according to fact sheets about the chemical.

Some Garden Grove residents filed a class action federal lawsuit on Saturday against GKN Aerospace Transparency Systems, which operates the facility where the tank is located. Lawyers for the residents argued that regardless of what happens, property values in the surrounding community are sure to be impacted.

GKN Aerospace did not comment on the lawsuit but has apologized to residents and businesses forced to evacuate. It said Sunday it was “working around the clock to mitigate the risk of a leak”.