DES MOINES, Iowa (AP) _ A spark ignited a spilled chemical and exploded in a fireball at a tire plant Wednesday, killing one person.

Thick, black smoke could be seen 10 miles from the Titan Tire plant. One square mile around the plant was evacuated because the leaked chemical, heptol, posed the threat of even bigger explosions.

The area was declared safe an hour after firefighters arrived and sprayed the scene with water.

Fire department spokeswoman Linda Frangenberg said a tanker was delivering heptol to the plant, but there was ``an error in the connection'' so the chemical leaked.

Police said the driver of the Bulkmatic Transport Co. tanker truck, Douglas Oswald, 25, of Plainfield, Ill., was killed in the fire. He was standing about 20 feet from the rear of the tanker when it blew.

One plant employee suffered smoke inhalation.

Officials from both companies did not immediately return calls.