JOHNSTOWN — An explosion that destroyed a house Monday night and left three people injured originated when two propane tanks malfunctioned, according to fire investigators.

Officials said Mike McGrail, owner of Big Mike's restaurant in Gloversville, and his wife, Debbie, were airlifted to University Hospital in Syracuse after the explosion at their home at 280 Elmwood Ave. Extension. They were listed in serious condition today in the hospital's burn unit.

Their son suffered minor injuries, was treated at Nathan Littauer Hospital and returned to the scene Monday night.

Fulton County Fire Coordinator Garth Hillier said the initial call for a house explosion came in at 7:12 p.m. When firefighters arrived, the family members were out of the house and firefighters assisted in getting them out of the rubble. The fire was brought under control in about 30 minutes.

"It was something that was pretty amazing," said Hillier. "What was a nice split ranch house is completely destroyed. It is literally flattened. There is insulation, boards and wood across the street. There were parts of the house in the trees surrounding the house."

Hillier said the two adults were in the basement and may have been searching for the gas leak, while their son was on the first floor when the explosion occurred. The son escaped through a window and Mike McGrath also got out of the house, while neighbors helped Debbie McGrath escape, Hillier said.

County fire investigation teams interviewed the victims and neighbors and determined the cause was two propane tanks at the rear of the home.

"We believe it was accidental," Hillier said. "There is nothing criminal, and the area of origin is the propane tanks."