The 28-year-old woman was lighting candles inside a parked motor home at about 10:20 p.m. when she picked up what she thought was another candle, police said.
It was actually a firecracker, and when she lit it, it exploded in her hands, police said. Her injuries were not life-threatening.
The motor home was parked in lot at San Bruno Avenue and Division Street, police said. She was transported to San Francisco General Hospital.