IRMO, S.C. -- Investigators say an electrical problem ignited a Christmas tree, causing a fire that killed a 5-year-old boy and his 18-month-old sister in their suburban Columbia apartment.

Irmo Fire District Chief Investigator Jeff Allen said the tree helped the fire to spread quickly after it started Wednesday morning.

The father of the children was asleep with his kids in upstairs bedrooms of the apartment when the fire started. The father tried to save his children, but got disoriented by the smoke and jumped out a window. The fire was then too hot for him to get back inside.

Allen says one or two sprinklers likely would have stopped the fire and saved the children. The building was built before South Carolina law required sprinklers in apartment buildings.