Los Angeles (United States) (AFP) - The threat of a toxic chemical tank explosion in Southern California has subsided enough to allow some of the 50,000 residents who were evacuated to return to their homes, officials said late Monday.

Garden Grove Police Chief Amir El-Farra said the downsizing of the evacuation zone came after new data and discussions with subject matter experts.

“For those that remain impacted, I know this may be frustrating. That number is approximately 16,000 of you. Please understand that we are doing this for your safety, and we will continue to work diligently,” El-Farra said.

Concerns that the flammable chemical in the tank could explode or leak toxic fumes prompted authorities on Friday to order evacuations in the heavily populated Garden Grove area of Orange County, southeast of Los Angeles and about five miles from Disneyland.

The tank contains 7,000 gallons (26,000 liters) of methyl methacrylate, a volatile liquid used to make plastics.

The crisis began late last week when authorities detected a leak in the tank, and subsequently a crack, though they did not say if the two were related.

“There is currently no active leak, and continuous live atmospheric monitoring confirms there are no chemicals leaking,” county fire officials said late Sunday.

On Monday, pressure in the tank was declining, and the temperature had fallen to 93F (34C) from 100F (38C), Orange County Fire Authority Incident Commander Craig Covey said.

“The crack is there. We have verified that it’s there, and the tank has released its pressure,” Covey said.

“That is incredibly positive news as we turn the corner on this incident,” Covey said.

Federal regulators had dispatched a team of experts to advise on possible outcomes, with Environmental Protection Agency (EPA) chief Lee Zeldin telling CNN on Sunday that the “most catastrophic scenario” would be if one tank exploded and caused other tanks nearby to explode with it.

However, Zeldin said “the most likely scenario” was “a low-volume release” enabling authorities to monitor, neutralize and contain the threat.

The tank is owned by GKN Aerospace, which operates 32 manufacturing locations in 12 countries, per its website.

The Birmingham, UK-headquartered company develops airplane technology and said in a statement Sunday that it is “working around the clock to mitigate the risk of a leak.”

Disneyland officials said the “resort remains open to guests,” and they were keeping close tabs on the matter.

The EPA says methyl methacrylate is irritating to the skin, eyes, and mucous membranes in humans. It can also cause respiratory and neurological reactions in cases of acute or prolonged exposure.