The exact cause of the natural gas build up is not known, but the evidence points to an explosion from inside the house not a gas line leading into the house from the outside.
A surveillance camera from a block away captured the exact moment of the explosion. In slow motion, a destructive fireball shot out into the night sky
"Like a boom and it just rattled all the way out through the house. I thought it was an earthquake," Gilbert Armstrong said.
Armstrong lives two doors down from the blast, and spent part of the morning washing parts of his neighbor's home off his cars.
On Monday night, once he realized it was an explosion and not an earthquake, he ran towards the damaged building and found 61-year-old Leon Spencer lying in his front yard on fire. "He was saying call Donna, call Donna," Armstrong said.
Armstrong immediately called next door neighbor Donna Miles.
"When I tried to open my door, the handle in my doorknob was hot and I just creepily opened and then I looked down and Leon was downstairs just saying, 'Donna, Donna help me, help me," she said. "And he was already on fire."
Neighbors say Spencer lives downstairs in this duplex and had been renovating the upstairs to rent. Some say the smell of gas was out here for days, and Miles got a whiff minutes before the blast.
"When I went into my apartment yesterday evening, after work, I smelled faint, it was so faintly," she said.
PG&E sent out a crew last night with natural gas detection devices and found no leaks along the perimeter of the house. A PG&E spokesperson says gas connections inside the house are the responsibility of the owner.
Oakland Fire Department told ABC7 there will be two investigations; one by PG&E and the other by city building department.
Miles is being cared for by the Red Cross until authorities can tell her when she and her great grandchild can house is structurally sound.
As for Spencer, he is hospitalized with burns to 80 percent of his body.