The city of Oakland, Calif., said officially this week that we might never know what caused the nation's worst structure fire in 14 years -- the Ghost Ship fire that killed 36 in the city's Fruitvale district.

All but one of the 36 victims were attending a late-night electronic music performance on the warehouse's second floor on Dec 2, 2016, and were overcome by smoke from a blaze that started on the first floor of the cluttered building. The onsite manager and his assistant have been charged with involuntary manslaughter and are being held in Alameda County Jail in Dublin, Calif., awaiting arraignment next month.

Formal report

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government investigators issued a 50-page "Origin and Cause Report" on Monday that found the fire started in the corner of the ground floor but caused so much destruction that the precise cause of the Ghost Ship blaze could not be determined after the fact. "No conclusive determination of the initial heat source or the first materials ignited was made," the report said. "The fire classification is UNDETERMINED."

The two-story building at 1305 31st Ave. was zoned as a commercial warehouse and did not have permission to accommodate live/work residents or to host live concerts. But the so-called Ghost Ship warehouse was well known in the San Francisco Bay Area arts community and even promoted itself on social media

The building had repeated visits from Oakland police and firefighters from a firehouse one block away, but city officials took no action to ordering the warehouse closed down or brought up to code.

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Instead, the live/work warehouse operated openly despite numerous complaints from neighbors about noise and debris accumulating on the sidewalk outside in the vacant lot next door.

Inhabitants

The facility had some 25 full-time residents living in makeshift living spaces assembled from old furniture, pianos and hanging rugs, and the clutter would have made it difficult to escape from the burning building. The lights, powered by an extension cord arrangement from the auto shop next door on 31st Avenue, went out shortly after the fire began, the report said.

Most of the victims died near the Ghost Ship's second-floor performance space. The main path down to the ground floor, where the exits were, was a stairway made up of stacked pallets that quickly was consumed by flames. A more traditional stairway was hidden behind decorations and was not known to most concertgoers.

Narrow escapes

More than 50 firefighters from three Oakland stations were needed to douse the flames. The report also includes an interview with survivors who were lucky enough to be near an exit when the smoke began to get thick, or were familiar enough with the structure to get out anyway.

One survivor told investigators that he was able to escape out through a window he remembered from a previous visit to the warehouse. The Ghost Ship had no fire alarms, no sprinklers and no lighted exit signs that could have been visible despite the thick smoke. One victim was found just 10 feet from the front door, the report said.

The fire was investigated by Oakland's fire and police departments, the Alameda County Arson Task Force and the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, the report said..