The two-alarm fire broke out Saturday afternoon in the Fleishhacker Pool house, which is located at the foot of Sloat Boulevard.
Thick smoke was pouring out of the building when firefighters arrived. Crews did not go inside.
"Upon arrival I went into defensive operations right away," Assistant Chief Tom Siragusa said. "This is an abandoned building. There's no reason for any life hazard to be concerned. The risk was too great for an abandoned building at this point."
One firefighter was rushed to the hospital and evaluated for smoke inhalation. No one else was injured.
The cause of the fire is under investigation.
The building, known for its striking interior, has been closed since 1971. Since then it has been home to squatters and the homeless.