Authorities in Southern California have evacuated about 40,000 people after a large tank containing a hazardous chemical on the premises of an aerospace giant began spewing vapor Thursday, according to reports.
Orange County firefighters responded at about 3:22 p.m. Thursday to “an aerospace manufacturing company in the 12100 block of Western Ave. in Garden Grove” after vapors escaped the relief valve of a 34,000-gallon tank containing methyl methacrylate and that had begun to heat up, the Orange County Fire Authority (OCFA) said.
The company at the affected location is GKN Aerospace, a U.K.-headquartered company that supplies commercial and military aircraft parts and products globally—including the windows on the Orion capsule in which the Artemis II astronauts traveled around the moon.
The OCFA labeled the incident a “unique hazmat incident.” Some 40,000 people were evacuated, with some describing the incident as scary and shocking, the Associated Press (AP) reported.
I’m proclaiming a state of emergency in Orange County as California continues to respond to the hazardous chemical incident in Garden Grove.@Cal_OES has been mobilized for over 24 hours and state agencies are supporting impacted communities to protect public safety, and assist… pic.twitter.com/pOLZWkX0vD
— Governor Gavin Newsom (@CAgovernor) May 23, 2026
Evacuees rest in the shelter while the news plays on a television after a chemical leak from a large storage tank threatened residents in Garden Grove, California on May 22, 2026. Tens of thousands of people were ordered to leave their homes in California Friday after a huge chemical tank began leaking, with warnings it might blow up, sending toxic fumes over a heavily populated area. (Photo by Blake Fagan / AFP via Getty Images)
Methyl methacrylate is a chemical used to make resins, plastics, water-repellent concrete, and dental cement and ceramic fillers, according to the U.S. Environmental Protection Agency.
The vapor from the overheated tank is “a fruity and heavy smell” and could cause irritation to the eyes, nose, respiratory tract and lungs, leading to symptoms such as sore throat, runny nose, burning eyes, and nausea, Dr. Regina Chinsio-Kwong, Orange County’s Health Officer, told the press late Friday.
Dizziness, headaches, and severe respiratory issues can result from prolonged exposure, Dr. Chinsio-Kwong added.
The vapor had not built to detectable levels in the air as of late Friday, Dr. Chinsio-Kwong said.
Authorities deployed an overhead sprinkler system and firefighting drones to some initial success, while also issuing evacuation orders to neighborhoods around the company’s premises and designating evacuation centers, according to the OCFA.
Residents returned home on new orders late Thursday following the initial success but by Friday morning the tank could not be secured, OCFA Chief and Unified Incident Commander Craig Covey told the press Friday.
A valve on the tank was found to be inoperable, stalling cleanup plans and prompting a reissue of evacuation orders and an expansion of the affected zones, the OCFA said early Friday.
Chief Covey told the press Saturday that while the initial firefighting operation successfully reduced the external temperature of the affected tank, it did not reduce the internal temperature in the tank, which kept rising.
***CRITICAL INCIDENT UPDATE***
Unified Incident Commander Craig Covey providing this morning‘s update. pic.twitter.com/er52WXgh3J— OCFA (@OCFireAuthority) May 23, 2026
The combined teams of firefighters, industrial chemists, and emergency response personnel went back on the offensive late Friday and discovered that the tank’s internal temperature had risen to 90 degrees, up from 77 degrees Friday morning, he said.
“We put [the teams] back in harm’s way last night, with an attempt to go in and neutralize the additional tank,” he said in part.
The teams have been brainstorming for either eventuality of a spill or an explosion. A spill would let out 6,000–7,000 gallons of “very bad chemicals” onto the parking lot on the company’s premises, while an explosion, which would result from a thermal runaway, would affect adjacent chemical-laden tanks, worsening the outcome, Chief Covey told the press. (RELATED: Septic Truck Explodes After Being Struck By Train, Video Shows)
“Letting this thing just fail and blow up is unacceptable to us. Our goal is to find something and not allow that happen, not let it damage our community, not let it damage our environment,” he said.
Should the tank fail, the teams have been developing “aggressive contingency plans” such as constructing dykes and dams to channel and contain the chemical as well as fire and medical emergencies for the teams confronting the high-risk situation round the clock as residents in the affected areas heeded the authorities’ calls to evacuate, lessening the risk of a more complex emergency response, he said.
“There are no reports of injuries at this time and our priority remains the safety of our employees, responders, and the surrounding community,” a GKN Aerospace spokesperson told the AP via email. “We will provide verified updates as soon as more information becomes available.”