GARDEN GROVE, Calif. (AP) — About 16,000 people remain under evacuation orders in Southern California as an overheated chemical tank still poses a risk to homes closest to the site, and officials Tuesday gave no word on when they might be able to return home.

The crisis forced 50,000 people to evacuate in and around the Orange County city of Garden Grove last week. A crack that formed by chance on the tank relieved pressure and helped avert a catastrophic explosion, allowing most evacuees to return home over the Memorial Day weekend.

But the risk of a smaller explosion or potential spill kept orders in place for about a third of the evacuees. Many are living out of hotel rooms, tents, emergency shelters at schools or staying with family or friends.

Isabel Mendez was among those still waiting to return to her mobile home. She said she broke out in a rash on her face and developed tingling lips and a sore throat while evacuating last week. After spending several expensive nights in a hotel, she is now staying with her mother in the Los Angeles area.

She remains uncertain about returning home because she does not trust official assurances that the area is safe.

“Of course it is still dangerous,” she said.

Exposure to methyl methacrylate — a highly flammable chemical used to make plastics — can cause serious respiratory problems, neurological problems and irritation to the skin, eyes and throat, according to the federal Environmental Protection Agency. The tank at GKN Aerospace Transparency Systems, which makes cockpit windows, canopies and windshields, contains 6,000 to 7,000 gallons (22,700 to 26,500 liters) of the chemical.

“We apologize for the ongoing disruption this incident is causing and our priority remains its safe resolution,” the company said, “so that residents can return to their homes as quickly as possible.”

Separately, an implosion of a chemical tank Tuesday at a pulp and paper mill in Washington state injured at least 10 people, while an undisclosed number of others had been killed or remained missing.

Crews at the California plant worked overnight to ensure two nearby tanks were neutralized and would not be affected by the compromised tank, Orange County Fire Capt. Brian Yau said.

The tank overheated because a valve on the cooling system failed that kept it at at 50 degrees, (10 degrees Celsius), said Orange County Fire Authority Division Chief Craig Covey.

Crews sprayed water on the tank until the interior temperature stabilized to 92 F (33.3 C), down from 100 F (37.7 C) over the weekend, the fire department said Tuesday. A sprinkler system is still dousing the tank, and the company said its technical specialists and firefighters removed insulation from the tank to help cool it.

So far testing has found no contamination, officials said.

Orange County Health Director Regina Chinsio-Kwong tried to reassure people returning home over the holiday weekend, saying "you should feel comfortable going home even if you’re across the street from that new zone line.”

Concern among residents

The crisis interrupted Memorial Day plans, graduation ceremonies and daily life in central Orange County, which is made up of a cluster of cities including Garden Grove.

The city of 170,000 people, along with neighboring Westminster, is home to Little Saigon, the largest Vietnamese community outside Vietnam, and is next to Anaheim, home to Disneyland’s two theme parks, which were outside the evacuation zone.

Henry Nguyen, a 56-year-old auto mechanic, and his family spent the first two nights sleeping in their car.

Days into the evacuation, Nguyen said he sneaked into their Stanton home, which was filled with fumes, to rescue the family’s dog, cat and betta fish.

He also got a tent, which he pitched by an emergency shelter that officials set up in a nearby park building in Fountain Valley. Nguyen said he’s trying to focus on the experience like it’s a camping trip in the heart of densely populated Orange County.

He even brought archery equipment to use at a range in the park to help his teenage daughter, who was back at high school Tuesday, keep busy until they can go home.

“There’s no time frame,” he said.

Environmental risks remain

The South Coast Air Quality Management District will monitor the air for several months and the EPA will be checking sewer and storm drains for spills, Orange County Supervisor Janet Nguyen said.

As the tank heated up, the chemical converted from liquid to gas, ramping up the pressure and explosion risk, said Andrew Whelton, a Purdue University engineering professor who has studied environmental contamination. Some of the methyl methacrylate may already have hardened into a stable plastic similar to plexiglass, reducing the danger, he said.

“The tank was on track for a catastrophic explosion,” Whelton said. “The formation of a crack seems to have allowed pressure to vent.”

The risk remains of a smaller blast that could send projectiles or even a chemical plume toward nearby homes, he said.

The tank needs to get closer to 60 to 70 degrees Fahrenheit (15.6 to 21.1 degrees C) before conditions are considered significantly safer, he said.

The California crisis is reminiscent of a 2014 chemical spill in Charleston, West Virginia when storage tanks failed. The disaster inspired a new state law requiring more inspections and registrations of aboveground storage tanks.

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This story has been updated to correct a quote’s attribution to Orange County Fire Authority Division Chief Craig Covey not TJ McGovern, an interim fire chief of the Orange County Fire Authority.

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Weber reported from Los Angeles and Bellisle from Seattle. Associated Press journalists Leah Willingham in Boston; Jamie Stengle in Dallas; and Ethan Swope in Garden Grove, California, contributed to this report.