Firefighters contending with a dangerously overheating industrial tank of a hazardous chemical in Southern California have eliminated the possibility of the tank exploding after a crack relieved some of the mounting pressure, they said on Monday.

Although the worst-case scenario for the tank of highly flammable methyl methacrylate had been ruled out, dangers remain, and tens of thousands of people remained under evacuation orders, the Orange County Fire Authority said.

The tank began overheating on Thursday at the GKN Aerospace facility in Garden Grove, a city of about 172,000 people roughly 32 km south of downtown Los Angeles.

By Saturday, California Governor Gavin Newsom had declared a state of emergency and evacuation orders had been issued for an area home to tens of thousands of people as fears mounted that the tank could rupture and spill up to 26,500 litres of toxic material or explode and endanger nearby tanks. Newsom on Monday said California had secured a federal emergency declaration for the incident from US President Donald Trump.

"This new federal assistance will further bolster our resources to help resolve this situation," he said in a post on X.

Firefighters celebrated the appearance of a crack in the tank over the weekend, which helped relieve pressure, and the tank had cooled slightly to 34 degrees Celsius from over 38 C.

"That is incredibly positive news," Craig Covey, a division chief at the Orange County Fire Authority, said in a video statement.

Firefighters have been dousing the tank with water to cool it, and have taken the risk of approaching the tank to check temperatures only after the sun has gone down, officials said.

GKN, a British company, uses its Garden Grove plant to make windows and canopies for commercial and military aircraft, according to its website, and has issued apologies for the disruption its overheating tank has caused to Californians.

Besides the fear of the tank exploding, officials have worried that the toxic chemical could leak, and that vapours expelled from the tank could cause respiratory problems in people after prolonged exposure, although air-quality monitors had not detected vapour as of the latest health update cited by officials over the weekend. (Reuters)



Edited by Cecil Wong