The Big Apple firefighter’s union is steaming mad over the sudden discovery of 68 boxes of Ground Zero health data following the Sept. 11, 2001 terror attacks — files they were told never existed. The recently surfaced boxes contain thousands of pages of information on possible toxins at the Lower Manhattan site that union members said could be used to add new ailments to the list of covered 9/11-related illnesses. Some 343 FDNY firefighters lost their lives at the World Trade Center site on 9/11 with hundreds more having lost their lives since from health-related maladies.