Many of the extras in the film are actual Chicago firefighters. A casting call was put out in a Department memo prior to the start of shooting. In addition, many suburban firemen participated in the funeral procession.
There are three arson victims, Donald Cosgrove, Alan Seagrave, and Jeffrey Holcomb. Cosgrove is after the real life Chicago Fireman/Author William Cosgrove who served as Robert De Niro's technical advisor for the movie. Seagrave is the name of a fire apparatus (fire and ladder truck) manufacturer. The firehouse where Engine 17 and Truck 46 were quartered is the real, in-service firehouse of the Chicago Fire dept's Engine 65 and Truck 52.
The numbers of the fire companies are all "dead" numbers in the Chicago Fire Dept. Engine 17, Truck 46, Engine 24, Truck 6 (now back in service as of March of 2004), & Engine 33, (referred to, not actually seen in the movie), are all out of service. The Chicago Fire Dept. has 24 battalions, battalion 25 was created for the movie.
The production company totally refurbished 6 pieces of fire apparatus, and upon completion of filming, donated 5 of them to the Chicago Fire Dept., who used 4 of them as front line equipment for several years, and one as a spare. The only one that was not donated to the city was the truck that was flipped over, which was totaled for that shot.
The photos of firefighters seen on the walls of the investigators office are of the Los Angeles Country fire fighters who were on scene during the filming of the fire scenes as a precautionary measure.
In an interesting twist of fate, Brad Pitt lost out on the role of Brian McCaffrey in Backdraft to William Baldwin, who then had to be released from his contract to play the small part of J. D. in Thelma & Louise that was re-cast with Brad Pitt.
The Fire Engine 17 used in the movie was purchased by a Volunteer EMS/Fire company in North Eastern PA and is currently under renovations to restore it back to active duty as a first due unit after several years of storage.
The Hans Zimmer score heard during the final scene of the movie can not be found on the official soundtrack. It is however on the album 'Passions And Achievements: A 20-Year Retrospective Of Soundtracks From The Films Of Director Ron Howard"'.