CONSTANTIA, N.Y. (AP) _ Thirteen volunteer firefighters battling a house fire survived a explosion that blew the sides off the two-story stone and wood-frame home.

Witnesses described one firefighter being blown out a door and another being trapped under building materials after a fireball burst through the house and flames shot 20 feet into the air.

``The thought on everyone's mind is how bad this could have been. They were blessed and lucky,'' said Terry Bennett, a spokeswoman for the Oswego County Emergency Management Office.

There were about 100 firefighters on the scene at the time of the explosion, she said.

Heather Grote had arrived home from work about 7 p.m. Wednesday and found her house filled with smoke. She asked neighbor Matthew Whaley for help and Whaley called 911, said Whaley's fiancee, Sarah Locke.

The two homes, and a half-dozen others, are located on a rural, dead-end street on the north side of Oneida Lake, about 15 miles northeast of Syracuse.

Whaley said he turned off a 500-pound propane tank outside Grote's home. The tank had been making a funny noise, Locke said.

When firefighters arrived, they began battling the flames and searching for the fire's source, Bennett said. Everything appeared to be under control when the explosion occurred, she said.

``It was a huge boom,'' Locke said.

Twelve of the 13 firefighters injured in the blast were transported to area hospitals. One firefighter remained hospitalized in fair condition Thursday.

The state Fire Marshal's Office was investigating the cause of the blast.