FREEPORT, Texas -- An explosion rocked a chemical plant Friday in Brazoria County, injuring workers and keeping neighboring residents locked inside their homes for hours.

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Workers Describe Explosion

The explosion happened shortly before 9:30 a.m. at BASF Corp., 602 Copper Road, in Freeport.

NewsChopper2 showed a thick plume of black smoke billowing from several tankers at the plant.

BASF officials said that a railcar exploded. It was carrying ammonia, cyclohexanone and oxime, which are used in the manufacture of nylon.

Ammonia is a colorless, pungent gas, extensively used to manufacture fertilizers and a wide variety of nitrogen-containing organic and inorganic chemicals. It can cause a burning sensation and cough if inhaled, and can cause skin to burn and blister.

Company officials released the following timeline.

• 9:10 a.m.: Employees were working on the railcar when a chemical release was reported.
• 9:20 a.m.: Area was evacuated.
• 9:30 a.m.: Explosion and fire were reported.

"The tank car over-pressured, causing the explosion," said Sharon Rogers, with BASF.

The fire was contained to the plant, but emergency officials asked people working and living in the area to take some precautions.

No evacuations were ordered, except for workers at the plant, authorities said.

"We have four minor injuries reported. No fatalities. (The injuries) are in the nature of cuts and scrapes," Rogers said. "All of our personnel are accounted for."

Six others, living downwind from the plant, complained of respiratory problems and were treated at local hospitals.

Officials said workers prepare for emergencies like this.

"They sounded the alarm and we went out to the assembly points. You could hear it leaking," said Jimmy Alexander, a plant worker.

"We looked out the door and it looked like a bomb went off," another BASF worker said.

"(It was a) big fireball with heat coming from it. And then I ducked to hide and then I saw pieces falling down," said Robert Sturdy, a plant worker.

"We just started running. Debris was just flying everywhere so we got to our bosses and we all got together and got to a safe assembly point," said John Nunez, a plant worker.

Shelter-In-Place Order

Emergency crews have issued a shelter-in-place order for nearby residents while the cleanup continues.

When a shelter-in-place is issued, nearby residents should:

Go inside
Shut all doors and windows
Turn off air conditioners and heaters to prevent outside air from getting inside
Turn on the radio to listen for instructions
Stay off the phone

Sheriff's deputies told News2Houston that roads around the plant at state Highway 332 and Copper Road were closed.

Motorists were asked to take FM 523 if needed.

BASF officials said that the community was not in danger, despite the incident.

Eyewitness Accounts

Witnesses said that the explosion shook their homes and that they could see a large plume of black smoke coming from the plant. The blast was felt 40 to 50 miles away, according to witnesses.

Esther Ramirez was at a Denny's across the street.

"We were eating breakfast and all of a sudden, it felt like the building had lifted and pretty much dropped and the windows shook. It almost was like a deafening sound and people started running. Of course, it was close enough to the plant so there was men who work in the plant sitting there eating also and they ran out of the restaurant with their cell phones trying to find some information. People immediately left the restaurant. It was very scary since 9/11 happened," Ramirez said.

Witnesses said that the explosion also blew the windows out of a nearby motel.

Ceiling tiles fell and other damage was reported at a convenience store across the street from the plant.

"It was very, very bad. I thought my store was coming on top of my head," said Victor, who works at the store. "Everything started to fall. The whole roof came down. I was really scared."

BASF Freeport Plant

BASF employs approximately 1,121 people at the plant, and 371 of those are contractors. There are 16 plants on site that make 11 different chemical products, company officials said.

The Freeport plant makes acrylic acid, which is used in textiles and plastics.

It's one of Freeport's largest employers.

Freeport is approximately 50 miles south of Houston and has one of the world’s largest chemical complexes.