A dangerous chemical leak that forced nearly 50,000 people from their homes in Orange County, California, may have taken a hopeful turn after crews discovered what officials described as a pressure-relieving crack in the leaking industrial tank.

Officials said Sunday the discovery at the GKN Aerospace facility in Garden Grove could change the strategy for handling the crisis, which has entered its fourth day.

“With this new information, it could change our trajectory and our strategy to this event,” Orange County Fire Authority Interim Chief TJ McGovern said in a post on X. “Last night was a successful operation for this emerging incident.”

The leak began on Thursday at the facility on Western Avenue in Garden Grove. Authorities expanded evacuation orders Friday to neighborhoods across Garden Grove, Cypress, Stanton, Anaheim, Buena Park and Westminster.

The leaking tank is estimated to contain about 7,000 gallons of methyl methacrylate, a highly flammable industrial chemical that can release toxic fumes and potentially trigger explosions if temperatures continue to rise. No injuries have been reported, but more than 50,000 residents were under an evacuation order over the Memorial Day weekend.

California State Sen. Tom Umberg said Sunday that the tank temperature reached 100 degrees during overnight operations, the highest reading possible on monitoring equipment, but said the newly discovered pressure release could help reduce the danger.

“That may avoid the two concerns that we all had,” Umberg said. “One was an explosion, the other was a leak of liquid material vaporizing into a toxic fume, a toxic plume.”

Just days earlier, officials warned the situation could end in catastrophe.

“There are literally two options left remaining: One, the tank fails and spills a total of about [6,000] to 7,000 gallons of very bad chemicals into the parking lot and that area,” OCFA Incident Commander Craig Covey said Friday. “Or two, the tank goes into a thermal runaway and blows up, affecting the tanks that are around it that have fuel or chemicals in them as well.”

Gov. Gavin Newsom declared a state of emergency Saturday to free up state resources.

“The safety of Orange County residents is the top priority,” Newsom said. “We are mobilizing every state resource available to support local responders and make sure the community has what they need to stay safe.”

Meanwhile, Orange County District Attorney Todd Spitzer announced an investigation into the incident and urged potential whistleblowers to come forward.

“I am indicating to employees who work at GKN: If you want to come forward and you want to be interviewed and you want to tell us what you know, now is the time,” Spitzer said.

Methyl methacrylate is a flammable, colorless liquid used in the production of resins, plastics and plastic dentures and is a hazardous substance regulated by the federal government.

The substance can irritate the lungs, eyes and skin and in high doses can cause reduced lung function, along with dizziness and memory problems, according to the Environmental Protection Agency. Air monitoring tests have so far found that air pollution around the evacuation zone is within normal limits.

If the temperature inside the tank rises, it will cause pressure to build as the methyl methacrylate converts from a liquid to a gas, increasing the risk of explosion, which could ignite other tanks at the site.

A blast that releases the chemical into the air would send it into a wider area, and could create vapors that are hazardous to inhale, according to Orange County’s top health officer, Dr. Regina Chinsio-Kwong.

“If you are not in the evacuation zone, we don’t expect any health impact,” Dr. Chinsio-Kwong said. “If you were told to evacuate, please evacuate.”