An explosion that leveled the top floor of an East Oakland duplex and severely burned the building's owner was not the responsibility of Pacific Gas and Electric Co., a utility spokeswoman said Tuesday.

A preliminary investigation of the structure at 2317 and 2319 87th Ave. determined that there was "no gas leak outside the building" when the blast occurred at about 8 p.m. Monday, said PG&E spokeswoman Brandi Ehlers.

Investigators say the explosion may have been caused by a natural gas line rupture, but the exact cause has not been determined.

Assuming that the explosion happened inside the two-story building, any liability would be on the part of the owner, Leon Spencer, 61, who suffered burns over 80 percent of his body, authorities said.

Spencer had brought in neighbors to remodel the upstairs unit in preparation for renting it, authorities said.

Spencer was in critical but stable condition at St. Francis Memorial Hospital in San Francisco, hospital spokeswoman Linda Gillespie said.

Spencer ran out of the duplex shortly after the blast, witnesses said.

A neighbor, Donna Miles, 63, said she had opened the door to her home and had seen Spencer yelling, "Donna, help me!"

"I did see Leon on fire," Miles said.

The upper unit had collapsed onto the lower unit, where Spencer lived, said Battalion Chief Melinda Drayton of the Oakland Fire Department.

The force of the blast also shattered the windows of a nearby residence at 2311 87th Ave. Three adults and a child who live there were evacuated and were being assisted by the American Red Cross, Drayton said.