Pulvermacher told reporters Friday afternoon that nothing had been ruled out as the cause of the blast. He said investigators were following up on reports of work being done in the vicinity of the explosion.

Fitchburg house explosion: Neighbor found victim in house debris Mike St. John found his neighbor, Brian Grittner, seated in a pond of pink insulation in what remained of his Fitchburg home. Two explosions had just leveled the building, leaving Grittner, prone and incoherent, but alive.

“We’re trying to determine what caused this and how we can prevent this from happening in the future,” Pulvermacher said.

The investigation had found no evidence of a leak or explosion in the underground gas distribution system, said Steve Schultz, a spokesman for Madison Gas & Electric. That would rule out an underground gas main rupture, but not necessarily a gas leak inside the destroyed house.

MGE did not receive calls for a gas leak prior to the explosion, and the company’s first responders were on the scene within 10 minutes to shut off gas to the residence, Schultz said.

“We completed a thorough survey of the area to ensure the safety of the surrounding neighborhood,” he said. “We are actively participating with the ongoing investigation.”

Grittner told his mother the last thing he remembered before waking up in an ambulance was opening up the refrigerator.

“It’s astonishing that he looks as good as he does,” Nichols said.