The fire was reported shortly before 5 a.m. in a townhouse on the 100 block of Tammy Circle, said Lewis Broschard, fire marshal for the Contra Costa County Fire Protection District.
Smoke and flames were visible from the first and second floors of the townhouse when firefighters arrived, one resident who had been able to escape was waiting outside. The resident told firefighters that another resident was still inside.
Firefighters located the second resident, a 60-year-old woman, on a sofabed in the living room on the ground floor, but she was already dead when she was found, Broschard said.
The fire began in the living room where the woman was found, but the cause remains under investigation. The woman's cause of death remains unknown pending an autopsy that is scheduled for Monday.
In addition to the extensive damage caused to the unit where the fire started, there was also damage to the attached units on either side, Broschard said. A total of four adults and four children were displaced, and the total structural damage is estimated at around $250,000.
The surviving occupant in the primary unit told fire investigators that smoke detectors in the home were not working. Broschard said the death underscored the importance of changing the batteries on smoke detectors twice a year and testing them once a month.
"The smoke generation in this fire was extreme. He barely had enough time to get out and unfortunately she didn't have enough time to get out," Broschard said.
"Had the smoke alarm been operational it would have woken them up sooner," Broschard said.