May 26 (UPI) — Officials have reduced the size of the evacuation order in southern California, as the risk of a tank full of chemicals exploding has ended.

About 16,000 people were still under evacuation orders, effective Monday at 6 p.m. PDT, down from 44,000 initially evacuated, as interim Orange County Fire Chief TJ McGovern said at a press conference that the “most catastrophic and worst-case scenario was mitigated and resolved.”

“It’s not over yet, and I want to re-emphasize that: It’s not over yet. We still have work to do,” he said.

Firefighters “still have to mitigate a fire and very small explosion concern, and also a spill potential,” McGovern said.

The evacuations were initially issued on Friday after a tank containing methyl methacrylate in Garden Grove, Calif., at the GKN Aerospace manufacturing plant started to leak vapor. That’s when Gov. Gavin Newsom declared a state of emergency.

The tank started to overheat on Thursday, started to bulge and reached what is called a “boiling liquid expanding vapor explosion.” Officials were concerned that the tank could either explode or fail.

On Sunday, the tank cracked causing a spill, reducing fears of explosion. About 60,000 people had been evacuated.

The reason the tank overheated was a faulty valve that is part of a refrigeration system that keeps the tank at 50 degrees Fahrenheit, Orange County Fire Division Chief Craig Covey said Monday.

“One of the valves in that system froze up, so [the cooling system] was no longer being circulated,” NBC reported Covey said. “And due to that failure, the tank went into the heating-up process because it wasn’t continuing to be chilled.”

At one point, the gauge showed 100 degrees, which was the highest temperature it could show. But by Monday, it read 93 degrees, Covey said.

Firefighters have doused the tank with millions of gallons of water to bring the temperature down, Covey said. A deluge sprinkler system has also eased the fire risk.

GKN Aerospace, based in Great Britain, issued an apology, saying the company is “fully focused” on working with emergency services to resolve the situation.

A proposed class-action lawsuit has been filed against the owners of the tank, USA Today reported.

The Orange County District Attorney’s Office said it created an anonymous tip line and online reporting form to gather information. The Environmental Protection Agency is involved in the emergency response, Administrator Lee Zeldin said.

“Our community is rightfully angry and, now that the threat has been reduced, our work will immediately prioritize demanding accountability from all responsible actors,” said Rep. Derek Tran, D-Calif., on Monday. “I’ll continue working with local, state, and federal partners to ensure our residents get the answers and relief they deserve.”