The employee, San Francisco resident Moustafa Algazawy, was changing a light bulb above some storage lockers at the 76 station at 101 S. Mayfair Ave. when he fell from the ladder he was on, Daly City police Sgt. David Mackriss said.
Algazawy was taken to Seton Medical Center where he was pronounced dead.
Firefighters initially said Algazawy had been electrocuted, but Mackriss said an autopsy will determine whether he died from electrocution or from the fall.
A manager who saw Algazawy fall suffered a heart attack, apparently from the trauma of witnessing the incident, Cal/OSHA spokeswoman Krisann Chasarik said. He was transported to Peninsula Medical Center with what Mackriss called a "a severe grief reaction."
Mackriss said the gas station will remain closed today while detectives and Cal/OSHA investigate the teen's death.