Investigators have determined that an explosion that leveled a house in St. Paul last fall and killed a man who lived there was accidental and likely caused by a natural gas leak inside the home.

John Lundahl, 80, died from his injuries at Regions Hospital a few weeks after the Nov. 23 blast in the 600 block of Payne Avenue.

On Friday, St. Paul fire investigators said a natural gas leak stemming from a fitting or valve probably caused the blast in the southwest corner of the house where the kitchen was located.

Xcel Energy and the Minnesota Office of Pipeline Safety completed testing on the supply lines on the exterior of the house, Fire Department spokesman Roy Mokosso said. The exterior gas supply piping passed the testing. Xcel Energy also reported the average gas flow at the home increased on the day before and the day of the incident, which is indicative of a leak, he said.

"Leaks are the main cause of gas-fueled explosions," Mokosso said.

The department's investigation was not able to definitively determine the ignition source, but an electric charge from either static electricity or an arc from an electrical circuit could have been the trigger, the report said.

"There were no other items located during the examination that could produce a high-grade explosion other than natural gas, which was present and supplying the structure prior to and at the time of the explosion," the Fire Department's report said.

The blast, which occurred around 8:30 a.m., sent flames shooting as high as 50 feet into the sky and pieces of the wooden house flying in all directions. Debris littered nearby yards and streets. Some debris was tangled in trees 20 to 30 feet off the ground. Many who lived nearby saw or heard the explosion and said it sounded like a sonic boom.

Five other nearby buildings were condemned by the city. Fourteen other buildings, including homes and garages, had damage such as broken windows and cracked walls and ceilings.

Tim Harlow • 612-673-7768