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”.