HOUSTON -- Cleanup at a chemical plant continued Sunday after an explosion shattered windows in nearby homes and set buildings at the facility ablaze.

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Team Coverage: Explosions Caught On Camera

The explosion was caused by a mechanical failure in a vessel, Houston Fire Department District Chief Tommy Dowdy said Saturday, but it still wasn't clear what vessel failed nor what type of product was in it.

He said the vessels remained too hot to approach.

State and federal environment officials were monitoring the scene at Marcus Oil and Chemical on Saturday as the Houston Fire Department stood by to cool any hot spots.

The plant makes polyethylene waxes used in paint and printing ink.

Dowdy said about half of the plant was damaged during the fire, which broke out shortly before 6 p.m. Friday. He said millions of bags of wax the plant produced melted and flowed out into a parking lot where firefighters at one point were working.

"It was six to eight inches thick in the parking lot," Dowdy said. "Once it started getting several inches deep, it was impossible to work in that area."

Dowdy said one firefighter was burned when he fell forward in the wax and used his hands to catch himself. The firefighter was treated at a nearby hospital. A second firefighter was also transported to a hospital after suffering a back injury and nine residents went to the hospital for treatment of minor injuries, he said.

The district chief said he believed some were treated for shock from the blast, which blew out windows at a number of nearby homes. The blast was heard as far away as Alvin, 24 miles southeast of Houston.

"We were all talking -- my family and I -- and we just heard this big boom. We went outside. My girls were already outside and said they saw this big, orange explosion, above trees and houses in the way. We could smell it," said Delia Torres, who lives five miles from the plant.

Other residents said they thought the explosions were loud claps of thunder or sonic booms.

"It was so powerful," said Connie Lara, a neighbor. "Our 35-inch color TV fell face down onto the living room floor. It was wedged in an entertainment center. Now the wall in the living room is cracked all the way across."

"I thought it was an airplane that crashed into something -- one of these buildings down here. That's just how bad it was," said Audrey Green, who witnessed the explosion.

The U.S. Chemical Safety and Hazard Investigation Board was sending a team to the site for a preliminary investigation.

Dowdy told the Houston Chronicle in Saturday's editions that the fire was believed to have started near storage tanks on the grounds, but he it was extinguished by late evening. He said that he did not know what had been in the tanks.

Explosions were still erupting from the fire 90 minutes after the blaze began. The fire went to three alarms at about 7:15 p.m. Approximately 120 firefighters battled the blaze for hours.

Five people were working in the warehouse at the time of the explosion and were not injured, officials said.

"We were working and we heard something explode," plant worker Miguel Trejo said. "We don't know what exactly happened. We heard the noise and the fire department came in and sent us all out."

Dowdy said firefighters were trying to limit the amount of water they poured on the fire to prevent any runoff from the plant, a seven-acre facility located in a neighborhood of single-family homes, apartments and industrial plants.

Lenny Ogle, manager of a Shell station half a mile away, said the initial explosion shot flames about 75 feet in the air. "It was a ball of fire straight up in the air," he said.

Houston Fire Department District Chief Phil Boriskie said that the hazardous materials team was conducting an evaluation. He said that there were no reports of chemical exposure.

Danny Perez, who works for the Precinct 6 constable's office, was playing a video game at his home in Pearland when the explosion occurred.

"I was playing Grand Theft Auto, blowing up people, and all of a sudden, boom," he said. "It shook my house.

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