COLUMBUS, Ohio (AP) _ A natural gas explosion blew out the rear of a duplex row house Tuesday, injuring nine people, including six firefighters and one gas company worker, officials said.

Fire Battalion Chief David Zwayer said the gas company worker was the most seriously injured. He was reported in stable condition with second- and third- degree burns over about 20 percent of his body.

Three firefighters were hospitalized, while the other three were released after treatment.

Two people who lived in the house, Charles Brooks and Christine Raad, were treated at a hospital and released after being hit by flying glass.

Brooks said he was moving an old furnace in the basement of the duplex when he apparently knocked a gas line loose.

Brooks said he called the fire department and Columbia Gas Co. The utility worker, William Rogers Jr., 32, of Plain City, went into the basement first.

''That's when it blew up,'' Brooks said.

Zwayer said natural gas explodes when it builds up to certain levels and is ignited either by a spark or a pilot light.

Lynn Reed, who also lives in the house, said her sister, Christine, Christine's son and Brooks were outside when they saw the flash, which knocked her sister and Brooks over.