Cast members Ed Sullivan, Robert John Burke and Jack McGee actually were New York City fire fighters before becoming actors.
In the pilot episode of the show, both Tommy and Lou are wearing the older long style FDNY turnout coats. Denis Leary got the coat he is wearing from the late Capt. Patrick Brown who was the most decorated FDNY firefighter.
The pilot was filmed in the Yonkers Fire Department Headquarters.
The parts played by John Scurti and Michael Lombardi were written specifically for the actors by Denis Leary.