Des Moines, Iowa10-29-2007Two interstate freeways in Iowa have been shut down by an explosion and fire at a chemical plant near Des Moines.One worker suffered minor injuries in the blast at the Barton Solvents plant.The fire has been burning out of control this afternoon, sending flames and clouds of black smoke soaring above the plant.Exploding barrels could be seen hurled into the sky.An emergency management official says 55-gallon barrels and 300-gallon tanks are exploding, and that there are concerns about loaded rail cars and truck tanks there.A transportation official says the decision to close Interstates 80 and 235 near the fire was made because of the thick smoke and the toxic fumes.