Little Rock ? A tanker car transporting flammable gas derailed in a switchyard and exploded in a ball of fire Saturday, killing one person and forcing the evacuation of hundreds of homes.

A plume of smoke covered the south end of the city, and at least seven people went to hospital emergency rooms with complaints of respiratory problems.

At least two homes were destroyed – including one where the victim died – and several vehicles were totaled in the quarter-mile area surrounding the accident, police spokesman Chris Rankin said. A 209-foot-long railroad bridge also caught fire and was destroyed, a Union Pacific spokesman said.

The propylene tank was still burning Saturday evening, but the fire was under control, Rankin said.

Union Pacific officials planned to let the tank burn out and estimated it would take until early this morning. Police canceled the evacuation order Saturday afternoon.

Initially, police thought the chemical involved was vinyl acetate, which releases poisonous fumes. Officers went door to door, urging thousands of people in a 2-by-5 mile area to move to the north side of town. Propylene is less dangerous.

A Union Pacific train coming from Chicago hit the back of another freight train in the rail yard, causing the eight cars to derail, said Union Pacific spokesman Mark Davis.