Officials lifted evacuation orders on Monday night for more than half of the 40,000 Southern California residents living near an unstable chemical tank that they had feared would explode.

Emergency personnel said they had averted the worst-case scenario of a major detonation, after struggling over Memorial Day weekend to contain the unstable industrial tank, filled with a toxic substance, in Garden Grove, California. But, officials stressed, the risk of a smaller blast or spill remained and they did not rescind the entire evacuation order.

Some 16,000 people who live closest to the site were still displaced as the Orange County Fire Authority’s standoff with the 22-year-old tank neared the end of its fifth day.

“It’s not over yet,” TJ McGovern, the fire authority’s interim chief, said at a news conference. “We still have work to do.”

Crisis Began Thursday

The crisis, which first emerged Thursday and eventually led to a presidential emergency declaration Monday, eased after firefighters reported that a crack had relieved intense pressure on the tank, helping to drop temperatures inside.

“The trajectory is headed in the right direction for the first time since Thursday,” said Thomas J. Umberg, a state senator who represents the area that has been evacuated.

“The challenge now is that people want to get back in their homes,” he said, adding, “and they can’t go back until it’s safe.”

Officials celebrated their progress Monday evening but said they did not know when the remaining residents would be able to go home.

Erika Ocana, whose house is among the closest to the plant and is still under evacuation orders, does not know when her street will be safe again — and officials’ muddled communications haven’t helped, she said.

‘Is It Going to Explode or Not?’

“Everything they’re posting and saying, they’re not really clear about it,” Ocana said. “Is it going to explode or not? When are we going to know? Are we going to be safe? They’re confusing everybody.”

On Monday afternoon, she decided she couldn’t wait for answers. Ocana, her four children and her mother had evacuated earlier in a rush, without knowing how long they’d be gone. And her mother, a diabetic, was running low on insulin.

Ocana and her 16-year-old son grabbed masks and drove to their cordoned-off block. A sheriff’s deputy allowed them through, she said, but he warned them, “If anything happens, you’re on your own.”

This article originally appeared in The New York Times.

By Reis Thebault, Heather Knight, Shawn Hubler and Christina Morales