With the recovery of bodies from the Oakland warehouse fire now complete, officials are now focusing their attention on determining the cause of the blaze that killed 36 people during a concert.
Authorities on Wednesday said they are examining all potential causes, including whether some sort of an electrical problem with a refrigerator and other appliances might be responsible. They stressed they have not made any final determinations.
Former residents of the warehouse have described it as a serious fire danger, lacking sprinklers and filled with debris, trash and old furniture. Photos from inside the building show a vast tangle of electrical wires as well as a heating system that appeared to be hooked up to portable propane generators.
At the time of the fire, Oakland officials were investigating the warehouse in connection with reports of code violations and safety issues. City officials said the building was zoned for use as a warehouse, not for housing or a venue for concerts.
Jean. M. Daly, a former arson prosecutor in Los Angeles and San Francisco who specializes in fire cases, said investigators are going to seek to determine where the fire began — "the area of origin." They will do this by studying burn patterns and the intensity of the fire.
"The heavier the damage, the longer the burn, the more likely it is the area of origin," Daly said.
In this case, she said, authorities have alluded to a 45-degree pattern of the burn near three appliances — a refrigerator, a smaller fridge and a toaster — suggesting that is where the fire might have started.
But uncovering the origins of the fire "will take a microscopic examination of the appliances and the wiring," Daly said. "That takes time in a lab."
She said the situation is rather like the chicken-and-the-egg problem: Did an appliance ignite the fire or did wiring to an appliance set the appliance on fire? She said investigators for the federal Bureau of Alcohol, Tobacco, Firearms and Explosives would take the parts of the appliances to their lab to examine the plugs, the motors and other parts.
At the same time, the investigators will examine the building's wiring and breakers for short circuits and overloads and do what is known as arc mapping.
"They are going to look for … signs that it burned before the appliances and the building," Daly said. "Once investigators isolate the cause, they can then seek to determine who is responsible."
Robert Rowe, a former Downey fire marshal and a fire investigator, said determining the age of the warehouse's wiring would be one of the first issues addressed.
"Have there been any upgrades to the electrical system or is this the original wiring? Back when this was a warehouse, its electrical system was designed for a particular purpose," he said. "But modern equipment, laptops, chargers, sound systems, air conditioners and fridges place a very different burden on the system."
Rowe said the building's electrical system might have been modified without permits. Circuit breakers may have been replaced with large amp breakers because they were tripping. "When you don't replace the wiring, that can overtax the system and overheat the wiring," he said.