Some scenes which take place in the Firehouse 51 kitchen are filmed in the actual firehouse kitchen, others are filmed on a studio set. If you see a door to the left of the cooking area, that is the studio set; if you see a drinking fountain, that's the actual firehouse.
Filmed in Chicago. Firehouse 51 is actually Station 18, which is located at 1360 S. Blue Island Ave in Chicago. "Molly's Bar," owned by characters Herman, Dawson, and Otis, is filmed in the real Chicago bar "Lottie's" in Bucktown.
The Self-Contained Breathing Apparatus (SCBAs) worn by the cast are Scott 4.5 Air-Pak 75s. This is one of the most popular brands and models of SCBA with fire departments across America for its durability, reliability, and ease of use. However, the masks worn by the cast members are unrealistic. They are nonfunctional and were made specifically for the series with the anti-fog interior facepiece and exterior voice amplifier removed, the lens elongated, and the regulator mounted at an odd angle to clearly show the actors' faces. These masks would fog badly if they were actually flowing air. Real SCBA masks are put on separately from the regulator, which is connected after the mask is on, and disconnected before the mask is removed. The air demand and exhalation valves make a loud noise when operating, and muffle the voice of the wearer.
Before starring as Firefighter Peter Mills, Charlie Barnett guest appeared in Dick Wolf's show Law & Order: Special Victims Unit in the episode "Gray" as Chuck Mills, a rapist, and in the Law & Order: Criminal Intent episode "Cadaver" as Dr. Sam Harris.
Some of the cast reappear in other Chicago shows as different characters for example Charlie Babbo (Ben Darrden) play a little boy who gets badly injured during a car accident in Chicago Med. All though these are two different characters they are both called Ben
Season 1 features a story arc in which Joe Cruz lets a gang member die by inaction. He goes to Lt. Casey (Jesse Spencer) to confess. Season 6 of House M.D. (2004) featured a story arc where Jesse Spencer's character Dr. Robert Chase committed a similar act.