San Francisco City Hall was still experiencing operational problems Wednesday morning related to a small electrical fire that occurred there the night before, city officials said.
The fire was reported shortly before 9:30 p.m. in an electrical vault in the building's basement.
The basement's sprinkler system was activated and fire crews responded, and the blaze was extinguished quickly.
Those in the building were evacuated, including hundreds of people who were attending a private reception for the U.S. Green Building Council's Greenbuild International Conference, San Francisco Department of Public Works spokeswoman Rachel Gordon said.
The cause of the blaze was still under investigation Wednesday, but authorities believe it was sparked by a problem with one of two electrical feeds into the vault, Gordon said.
City Hall was operating on generator power Wednesday morning.
The third and fourth floors of the building had only intermittent power and many city employees were working off-site as a result, Gordon said.
The first and second floors, which contain various city departments, were open for business. Crews had brought large temporary lights into the Board of Supervisors chambers on the second floor, where only half of the overhead chandeliers were lit.
Mayor Ed Lee said he has surveyed the damage, and that there was water about 2 or 3 inches deep in parts of the basement.
"Everyone did a good job," Lee said. "We're making sure we investigate everything that could have been compromised by the intense heat."
Authorities said the city's Elections Department, which is located in the basement of City Hall, was unaffected by the fire.
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