Scores of firefighters battled the fire. In just three hours they poured 1.8 million gallons of water on the blaze, according to data compiled by the San Francisco Public Utilities Commission.

The fire damaged seven businesses: five in the building that went up in flames and two others nearby. No one was living in the upper floors of the building but 15 residents in adjacent structures were displaced.

The blaze also led to a political skirmish involving Supervisor Aaron Peskin, who criticized Fire Chief Joanne Hayes-White over how the Fire Department battled the blaze. Peskin apologized days later.

De Cossio is declining to release the name of the restaurant where investigators believe the fire started, citing an ongoing investigation. The four eateries on the first floor of the building are Tuk Tuk Thai Cafe, Ferry Plaza Seafood, the Salzburg and Rogue Ales Public House.

All seven of the businesses impacted by the fire have applied for disaster mitigation funds, according to the Office of Economic and Workforce Development.

The structure that went up in flames has 11 separate owners, including several trusts, and was built in 1914, according to the San Francisco Assessor's Office

De Cossio says because the building is so old, sprinklers and fire alarms were not required to be installed in businesses on the first floor.

A series of large fires in San Francisco several years ago prompted some officials and tenant advocates to push for more of the city's older apartment buildings to be equipped with sprinklers.

The last time a fire official inspected the first floor of the building was in July 2016, according to De Cossio. The department inspects businesses like the restaurants on the ground floor only when prompted by complaints -- not on an annual basis, he said. Crews last inspected the upper floors in 2014.

The fire spread so quickly and got so big because of the construction being done on the building's two vacant residential floors, De Cossio said.

"The building was in a compromised condition because it was under construction," he said.