LEWISTON — A joint State Fire Marshal’s Office and Lewiston Fire Department investigation into an explosion that injured five people at the Great Falls Balloon Festival on Saturday determined that the blast was caused by a mechanical malfunction.

The investigation concluded Monday, Steve McCausland, spokesman for the Department of Public Safety, said. Fire marshals, along with Lewiston fire officials and representatives from the Federal Aviation Administration and the state propane board, found that a malfunction on a propane tank valve led to the explosion, which was triggered by the pilot light, McCausland said.

The conclusion “coincides with what the pilot told investigators on Saturday,” McCausland said.

Other than “minor singeing,” McCausland said, “there was no permanent damage” to the balloon and equipment. McCausland said it was possible that the balloon could be back in the air in the near future.

The instantaneous fireball injured five of seven people waiting for takeoff in the basket of the hot air balloon named Passion during the festival’s Saturday evening launch.

Pilot Andre Boucher of Derry, N.H.,was released Monday from Maine Medical Center in Portland after being treated for his injuries, a hospital spokesperson said.

Twelve-year old Mason Mahonen was also treated at Maine Medical Center and released on Monday, the spokesperson said.

McCausland said he could not recall another hot air balloon accident requiring fire marshal investigation in Maine.