During opening 1971 sequence, an 80's style Dodge Caravan can be seen parked on the street while the firefighters are in route to the fire.
A cobra street lamp is present in the 1971 scene. They were not in use back then.
In the 1971 scenes we can see buildings that are retrofitted with brown thermopane replacement windows. These types of windows were not comon until the early 1980s.
Throughout the movie, numerous firefighters are seen *not* wearing their air packs.
In the opening scenes, Dennis McCaffrey is wearing an officer's helmet that reads "Engine 17". But, going to the fire, he climbs into the officer's seat on the ladder truck. If he was wearing the Engine 17 helmet, his place would have been on the actual engine. To ride the ladder truck, his helmet would have read "Truck 46".
The first victim's body doesn't land on the car after the explosion, but is there when firefighters arrive.
When Brian and Jen are on the fire truck, Jen's bra starts out lying on top of a hose, jumps back on her body and then disappears altogether by the time she has her jacket on.
In the apartment fire, Stephen goes in to save a little boy. When there's an explosion, Brian falls back and his boots are all the way up, on another shot when he's on the floor his boots are folded down.
The position of the keys dropped in the theatre.
In the final fire scene, both brothers are swimming in an elevator shaft filled with water, but as they are trying to escape that building moments later, there is no water running off them, or in their boots.
At the end of the movie the fire trucks exit the south facing doors of the fire house and we can see a setting sun in the western sky in the background. When they are filming from an aircraft, we can see the Chicago skyline with the first light of sunrise in the background. The only way you could view the Chicago skyline after sunset is from a boat on Lake Michigan. If it was evening in the view from the aircraft, there would be a lot more traffic on the roads. The scene was likely filmed early on a Sunday morning to minimize traffic disruption.
In the apartment building, Tim puts on his mask when he sets off with Steve to check the rooms. When we see them coming down the corridor, Tim is neither wearing nor carrying his mask.
When Brian McCaffrey climbs the ladder to the top of the chemical plant fire, the angle is so steep that he is required to use his arms to keep his balance. But, when he gets to the top, we see the angle of the ladder has been lowered.
In the sewing company fire, the woman that was rescued (woman in green dress) can be seen in the crowd outside of the building as 17 is approaching the building.
At the fire at the theater, Donald is holding the electrical plug with the crowbar, but in the next shot, he's got his hand on it and in the next shot, it's back to the crowbar.
When Steven and Axe are hanging from the platform, Steven's grip switches from overhand, to underhand (as he is trying to pull them both back up), and back again (just before they fall).
In the last scene the trees have green summer leaves as the trucks exit the house. During the ride, they are passing trees that do not have leaves because it is winter.
When Brian is talking to the Alderman during the retirement party, his fork alternates between the plate and his mouth between shots.
When Bull drives Bryan at home his arm changes position repeatedly between shots.
When Brian jumps aboard the ladder truck for the final fire he was just carrying his coat, now he's wearing it.
When Rimgale has Brian lift the trash can to prove his theory on how the arsonist was creating backdrafts, Rimgale is smoking a cigarette. The cigarette repeatedly changes length becoming longer and shorter, and then longer again in each shot of Rimgale. There is no time for Rimgale to smoke a whole cigarette, then light another one and smoke most of another in this short scene.
The fire truck crashes onto its side twice.
During the first fire, Stephen has a door chuck in his helmet when he comes through the door. When he is talking to Brian, the door chuck is gone.
The position of Brian's hands and arms when he is in the bar talking to the bartender right before Tim reads his station assignments. In one shot, they're holding the beer glass, in another shot, they're folded and in another shot, he's eating.
When Brian goes to talk to Ronald at the mental hospital, Brian lays out some reports and pictures on the table. Ronald picks up a report and starts to read while Brian asks him who's doing this. The top page of the report that Ronald has in his hands changes positions in between shots several times.
Several establishing shots of Co. 17 engines headed to fires early in the movie show them crossing a Chicago River bridge with Merchandise Mart in the background soon after leaving the firehouse indicating that Co. 17 is located near downtown Chicago. At the end of the movie when the pull back shots shows Co. 17's engines headed towards the fire, the skyline of downtown Chicago is considerably further away, indicating a location on the west edge of the city of Chicago
During the "you go, we go" sequence, lighting equipment is visible several times
The stunt mat that Shadow lands on after the explosion.
Reflected in the screen door after the "stinking spinach" line.
In the warehouse fire, when Bull is holding onto Axe and the explosion knocks them off the platform, you see Bull dangling from his "harness" and reaching for the beam in mid-air for a split second before the camera angle changes.
The paramedic doing CPR on Steven in the back on the ambulance at the end is doing it wrong, she is bending her elbows when she pushes on his chest, you are supposed to keep your elbows straight thus putting more pressure on the chest.
At the end of the movie the driver of the ladder truck is shown smoking a cigarette in the truck. Smoking is expressly forbidden in any city vehicle.
Experienced firefighters would know better than to ride elevators in buildings where fires may or may not be in progress.
In the final factory fire scene when Kurt Russell is wounded on the catwalk, the two firefighters who trying to get to Kurt are covered by William Baldwin spraying and soaking them with the water hose. One guy is wearing a hat and as the two reach Kurt, he takes off his hat and his hair is completely dry (as if he just got out of his dressing room). Though the hat would cover his hair from the water, he would still be sweating profusely due to the intense heat and wearing a heavy firefighters jacket.
The pressure dials on the fire truck at the garment factory all read zero.
Just as the department goes to a call when the hippies are around, you can see the overhead light-bar on while the fire bell rings.
In the garment factory fire when Brian goes off searching for a person, there is a drain on the floor and you can see the fuel the crew spread on the floor, the camera then cuts to a different angle and when it returns the fuel is on fire.
In the opening scene, Dennis McCaffrey is verbally referred to as "Captain" a number of times. However, while responding to the fire in which he is killed, he is shown wearing the lapel pin of a Lieutenant (Single Bugle on red background) instead of the lapel pin of a Captain (Double, Parallel Bugles on red background).
When Bull is in the back of the ambulance and he starts crashing, the paramedics give him lidocaine to settle his heart rhythm. Lidocaine isn't given in severe trauma patients, because one of the side effects is hypotension, something he already has from the blood loss.