The FDNY Commissioner position has usually been held by former members of the department, including former Chiefs of Department, Staff Chiefs, Deputy Chiefs, etc. It does not say anywhere that a civilian (non-FDNY) cannot be appointed the position, and it is ultimately the decision of the Mayor of NYC. Obviously, for many reasons, it is better for the department if a former FDNY member is given the position, however, Mayor Bloomberg hates the FDNY and will probably end up appointing someone else that un-qualified for the position.