CROSBY, Texas -- It happened at 2 a.m. local time Thursday: the first of two explosions at an Arkema chemical plant lit up the night sky in Crosby, Texas. The explosions sent a cloud of acrid smoke into the air, and more than a dozen sheriff's deputies to the hospital.

By morning, a fire was still burning.

A 1.5-mile radius around the plant had been evacuated Tuesday after company representatives warned local officials their emergency plans had failed.

"We believe the smoke is a non-toxic irritant," said Harris County Sheriff Ed Gonzalez.

The company had backup generators, all of which failed. Then, refrigeration units in three of nine trailers failed, reports CBS News correspondent David Begnaud.

The Arkema plant in Crosby, Texas on Thursday morning. CBS News

Officials warned that the highly combustible compounds, known as organic peroxides, were sure to burn as the temperature rose, although they downplayed the harm.

Arkema executive Richard Rennard defended the company's response.

"No one is in danger based on the fire that we expect," he said. "We believe at this point that the safest thing to do is to allow the other eight containers -- the product in those -- to degrade and burn."

The Environmental Protection agency reports it hasn't detected any concentrations of toxic materials in the air.

Arkema gave CBS News a list of all the hazardous chemicals there.

It wouldn't give us the exact locations of those chemicals, citing national security concerns, but claims it stored them a "good distance" from the trailers that remain at risk of bursting into flames.

Richard Rennard, left, and David Begnaud. CBS News

"I just have a simple question," Begnaud said at one point. "Regarding the chemical, can you tell us what it is and exactly what it contains?"

"Yes, it's liquid organic peroxide," Rennard replied.

"So what is it that makes it so worrisome?" Begnaud asked.

"The concern is that when these things degrade, they generate heat. When they generate heat, they can burn. And when they burn, you can have an explosion," Rennard said.

The Occupational Safety and Health Administration inspected Arkema's Crosby facility last year and found ten serious violations. But experts say it's premature to speculate whether or not they were related to Thursday's explosions.

On Thursday afternoon, the U.S. Chemical Safety Board launched an investigation into what happened.