Firefighters contain the blaze at a Texas chemical plant but a mandatory evacuation order remains in place

Tens of thousands of residents had evacuated their homes by Thanksgiving day following a series of explosions at a Texas chemical plant, Jefferson County spokeswoman Allison Nathan Getz told CNN.

Firefighters have made progress suppressing a Texas chemical plant blaze but authorities are keeping a mandatory evacuation order in place as a precaution.

Tens of thousands of residents within a 4-mile radius of the TPC Group plant in the small city of Port Neches evacuated their homes Wednesday after a series of explosions at the site, according to Jefferson County spokeswoman Allison Nathan. The chemical fire continued to burn on Thursday.

Jefferson County Judge Jeff Branick, who issued the mandatory evacuation, said Thursday firefighters were spraying water cannons over the blaze so the water vapors could cool the fire, causing it to burn out. The fire was contained but Branick said he wasn't prepared to lift the order until he felt it was safe for residents to return.

"I can confirm that the situation is improving, but we are not completely out of the woods as yet," Branick said.

Officials will meet at the plant early Friday to decide whether it's safe enough to lift the evacuation order, he said.

"I can't say that it's controlled. Whenever I can say that it's controlled, then I'll feel that the community is safe from another explosion," Branick said.

The first explosion at the plant rocked Port Neches early Wednesday. More explosions occurred during the day, including one that launched a tower into the air "like a missile," Branick said.

The blasts shattered windows, destroyed roofs and left residents fearing for their safety after officials initially urged them to "shelter in place."

Eight people injured in the blast were treated and released, Branick said. Three of the injured worked for TPC, a company spokesman said.

TPC has not yet said what caused the explosion and has not described the extent of the damage.

Branick, who issued the mandatory evacuation after the afternoon blast, said he was sorry for "any plans that might have been interrupted."

"I know that it's extremely frustrating, particularly on the eve of Thanksgiving, for you to be away from your homes and family, and I can feel your frustration," he said at a Wednesday news conference. "But I want to emphasize that the safety of the community is always going to be our top concern."

Officials told residents not to worry about their belongings, adding that they have increased patrols in the areas of evacuation to prevent looting, CNN affiliate KPRC reported.

Besides Port Neches, Branick's evacuation orders included the cities of Groves, Nederland and the northern part of Port Arthur.

But the chemical levels in the air tracked about 4 miles away from the explosion are "well below concentrations of health concern or odorous levels," the Texas Commission on Environmental Quality said.

In the hours following the first explosion, black debris floated in the air, CNN affiliate KTRK reported.

"The black stuff floating, don't touch it," said Troy Monk, TPC Group's director of health safety and security.

The plant makes products for chemical and petroleum companies, TPC Group said.

The fire is burning a chemical called butadiene -- a colorless gas with a gasoline-like smell that is considered a health hazard, according to the US National Library of Medicine. Butadiene is made from processing petroleum and is used to make synthetic rubber and plastics.

The health effects

Health effects from butadiene exposure can vary, the Occupational Safety and Health Administration says.

Lower exposures can cause irritation to the eyes, throat nose and lungs as well as cause frostbite. Higher exposures can damage the central nervous system or cause symptoms including distorted blurred vision, vertigo, general tiredness, lowered blood pressure, headaches or nausea.

More chronic effects are disputed, the agency says.

"Several human epidemiological studies have shown an increase in cardiovascular diseases and cancer," OSHA says. "However, due to the small numbers of cancers and confounding factors such as smoking, and simultaneous exposure to benzene and styrene, a true causal relationship cannot be established."

Experiments on mice and rats showed there was a "strong causal relationship" between butadiene exposure and cancer, the agency said.

CNN's Darran Simon and Sheena Jones contributed to this report.

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