One person died after a four-alarm fire sparked by a plumbing torch ripped through a Lowell apartment building Tuesday afternoon, authorities said. An elderly man making repairs with the torch in a bathroom on the second floor of the Central Street building is believed to have started the fire by accident. The body found Wednesday morning was probably that of the man, the state fire marshal’s office said. The Office of the State Medical Examiner will make the official identification. Firefighters battling heavy flames were unsuccessful at rescuing the man, the Lowell Fire Department said. The building had an ethnic market on the first floor and residences on the second and third floors.