This story was originally published by the Texas Tribune, and has been updated.

The owner of a flooded-out chemical plant in Crosby said early Thursday it received reports of explosions at the plant.

Arkema Inc. said the Harris County Emergency Operations Center notified the company at 2 a.m. Thursday of explosions and black smoke coming from its Crosby plant, which was inundated by Hurricane Harvey's floodwaters.

But the Harris County sheriff Thursday morning described the incident as a chemical reaction, not an explosion.

The development comes a day after Arkema warned that the organic peroxides used in the site’s manufacturing process had begun to heat up after the plant lost its primary source of power and backup power from generators. Without electricity to power refrigeration, the chemicals were expected to degrade, possibly leading to some type of explosion or fire.

The plant has nine vans, each with 36,000 pounds of organic peroxide stored in cardboard containers. Containers in one of the vans popped and caught fire, producing smoke that wafted 30 to 40 feet into the air, local officials told reporters early Thursday.

Arkema expects each of the vans will eventually ignite as they lose power and refrigeration.

“Please do not return to the area within the evacuation zone until local emergency response authorities announce it is safe to do so,” the company’s statement said.

Assistant Chief Bob Royall, with the Harris County Fire Marshall, told reporters the chemicals inside each van that loses refrigeration “will burn with intensity until the fuel is consumed, and then they will die down again.”

His office and the Harris County Sheriff’s Department downplayed environmental and public health risks from the plant, going as far as suggesting that “explosion” was not the proper terminology for the chemical reactions in the vans.

“They were different organic peroxides of different grades that were released, and it created a pop in the containers where they were being stored,” Sheriff Ed Gonzalez told reporters. “It wasn’t an explosion, I want to be very clear.”

“We just don’t believe there’s any further threat, even to the broader community. Even if somebody stayed behind in the active zone,” Gonzalez added. “We just want to manage the narrative a little bit, to make sure people don’t get in a panic if there doesn’t have to be.”

The county has been consulting with Arkema and outside experts since early Tuesday about how best to handle the chemical reactions.

“We’ve developed what we consider a very safe plan,” said Royall. “Everything is going exactly as we expected.”

“If you want to call it an explosion, there’s a technical definition, and I’m not going to get into that,” he told reporters.

Fifteen sheriff’s deputies at the scene were taken to the hospital Thursday morning after reporting that smoke had irritated their eyes and throats. All have been released, the sheriff’s office tweeted at 9:20 a.m.