Clyde Watarai, 57, a 16-year veteran of the department, died Wednesday after a long battle with lung cancer, according to SFFD Local 798.
His death came little more than a week after that of Lt. John Murphy, 49, a 24-year veteran, died from melanoma on Jan. 28.
Murphy was originally diagnosed with melanoma on his neck in 2010 that he had developed through repeated exposure to carcinogens while fighting fires, the union said. While it was successfully removed then, his cancer returned two months ago.
"Our hearts are heavy with grief this week as we bury these two men," Tom O'Connor, the union's president, said. "Cancer is becoming an epidemic within the fire department and we must develop new and aggressive methods of protecting our firefighters."
Murphy and Hatarai make five firefighters that have died of cancer in the last five months, the union said, including Capt. Dan Armenta, 63, a firefighter for 31 years who retired in 2010 and died on Oct. 25.
A study by the National Institute for Occupational Safety and Health and the U.S. Fire Administration released in October last year found elevated cancer rates and deaths from cancer among nearly 30,000 firefighters in San Francisco, Chicago and Philadelphia.
The study found that higher rates cancer of respiratory, digestive and urinary systems accounted for most of the increased risk. Firefighters in the study also had a risk of mesothelioma, a cancer associated with asbestos exposure, that was two times higher than that in the U.S. population as a whole.