FORT WORTH, Texas  —  A series of explosions rocked a chemical plant Thursday and set off a raging fire, injuring three people and sending up a pillar of black smoke that could be seen 30 miles away.

The cause of the fire was not immediately known. Workers at the Valley Solvents & Chemicals (search) plant told authorities they heard an explosion and then noticed a fire near a tractor-trailer that had just pulled in to deliver chemicals, said fire Lt. Kent Worley.

The driver suffered a burned leg, one employee had arm burns and another hurt his back trying to flee, Worley said.

Firefighters battled the blaze for about three hours after the blast, and the fire had diminished by late afternoon.

It raged in and around more than a dozen large metal and plastic tanks containing 2,000 to 4,000 gallons of methanol, sulfuric acid, hydrochloric acid, ethanol and other chemicals.

The Environmental Protection Agency (search) has sent an official to the scene with air-monitoring equipment to provide information to local officials, said Cynthia Fanning (search), a spokeswoman for the EPA in Dallas.

Valley Solvents officials didn't immediately return phone calls seeking comment.

The blaze was in a large industrial area not close to any residential neighborhoods.

"It shook all the buildings here," said Angela McCollum, who works at a cement plant about 100 yards away. "All I can see is just tons of fire and tons of smoke, and it's really kind of scary."