Factual error: When Roy is electrocuted and falls from the roof, after Karen uses the defibrillator paddles on Roy, she lifts both paddles, looks at the EKG monitor and says "He's converted." How exactly could Karen have known that he's converted? It's impossible for the EKG monitor to show anything at all. Either the defib paddles have to be in contact with Roy's body for the "quick-look" to get a reading, which they weren't, or the ECG electrode discs have to be on Roy's chest connecting him to the EKG monitor, and they weren't. As an aside, just watching Marco having problems attaching the air mask, and quickly glancing up towards the camera frustrated, then giving up is priceless.
Other mistake: On scene at the traffic accident, when the woman and the boy with non-serious injuries are seated at the back of the ambulance, neither Roy or Johnny are going along with them to Rampart, yet Johnny puts the drug box inside the back of the ambulance with them, and the ambulance drives off. With their drug box! Captain Stanley even says that he'll advise dispatch that they're available for a run at the scene, while the guys will be looking for the dog.
Other mistake: While Roy is showing Brice the squad, after Brice annoyingly locks Squad 51's side bay door, he asks, "How about the OB box?" but the subtitles read, "How about the OV box?" Then a minute later Brice says, "Let's look at the OB box," and again the subtitles read "OV box."
Audio problem: When Vince and Mike pull the tabletop out from under the car, while Roy is under there with Mrs. Merkle, we hear the audio of Roy loudly saying, "I'm telling you right now, we're gonna have to brace this thing well, this thing will...," but what's oddly funny is that the dialogue is dubbed right over Roy saying, "Wait, wait, let me check her over...," which is a neat trick that he can say both lines at the same time.
Other mistake: After Johnny takes Captain Stanley's BP, when Chet tells the guys, "Animal fat is the root of all evil," and also after John jokes, "How to survive on no meals a day," check out Roy's feet because he's wearing shoes (looks like black sneakers) that are below the ankle, with no socks. Then in a few moments they're all dispatched to the 'possible heart attack' and when they're at the scene, while Roy is sitting with the patient, he's wearing socks and his uniform shoes (their tops are above the ankle) as usual.
Visible crew/equipment: During the fire late at night, after Johnny and Roy run to the burning house, when Captain Stanley tells Chet to get the exposure and later warns to watch for spot fires, the moving shadow of the cameraman/camera is visible on the ground, right beside Captain Stanley's shadow.
Other mistake: Roy uses the Biophone when he tells Brackett the vitals of a woman with cardiac symptoms, and then Johnny uses the landline to tell Brackett that there's "Another victim, female, 8 months pregnant, she's gone into labor." Brackett responds, "The mother's probably had an MI... Any cervix dilation on the daughter?" It is impossible for Brackett to have known that the two women are related, let alone that they're mother and daughter.
Visible crew/equipment: When all the guys are on site of an overturned tractor trailer, Captain Stanley says "Let's cool off that cab." In the next closeup of Stoker spinning a gear, the reflection of the cameraman (with mustache and hat) holding a handheld camera is visible on the engine's red surface.
Visible crew/equipment: When Roy and Johnny leave Rampart and are heading back in the squad, about 16:40 minutes in, as they are discussing whether Roy has told his wife about house hunting, you can see two signs on the ceiling of the squad's cab. The signs say 'Emergency Saturday 8PM Rehearsal Mark VI Prod'. Possibly they are magnetic signs for the squad doors so people don't mistake the squad for a real fire department vehicle? (00:16:20)
Visible crew/equipment: At training center, after 18's guy falls into the trench with the sulfur trioxide, as they're removing his turnout coat just as Roy opens the drug box, seen behind Marco are four crew members who are near the tanker with the sulfur trioxide, past the trench.
Other mistake: When Johnny prepares Chef Michel's recipe, he leaves the casserole dish in the oven while Station 51 is dispatched to the structure fire. When he and Roy return, Johnny opens the hot oven door to find it smoking and the dish bubbled over, and even though the oven door is supposedly very hot, Roy places his hand on the inside of that door and actually leans on it like there's absolutely no problem.
Visible crew/equipment: While Roy and Johnny are climbing up to rescue the boy on the bridge, there's a closeup of the boy as he breathes heavily. When this shot pans to the right we see Roy (his stunt double actually) place the rope behind his back, and a mysterious dark gloved hand quickly appears behind Roy (and it's not Johnny's hand).
Other mistake: At the chemical plant, when Captain Stanley gets to the roof and realizes they have to shut off the main valve, over the HT he says, "Engine 8, HT 51, shut off the power..., Engine 15 supply Truck 8...," but the weird subtitles read, "Engine 80, Team 51, shut off the power..., Engine 15, Supply Truck 80..." Then a bit later Captain Stanley tells Mike over the HT, "Engine 51, HT 51, charge the line," but the subtitles read, "Engine 51, Team 51, start your line." Then as soon as Mike charges the line, Captain Stanley tells Roy and Chet, "Okay, full fog, full fog...," but again the weird subtitles read, "Okay, hold strong, hold strong."
Visible crew/equipment: While rescuing the invalid, when Roy climbs out of the second floor window he suffers an electrical shock, and when he falls in the closeup we can see the crash mat that he lands on when part of it flips up from the force of his weight. Also note that all the shrubs below the window have vanished.
Revealing mistake: After Johnny joins Roy in the ambulance and the patient flatlines they continue to Rampart, and when Brackett asks 51 for a strip, if we look out the window that's beside Johnny, we can see GlamourTrams in the distance. And when Roy says, "Isopeterenol drip, 10-4," we can see GlamourTrams right outside the window. They are driving around Universal's lot while shooting the footage inside the ambulance.
Continuity mistake: When Dixie shows Johnny the newspaper, Johnny reads the ad aloud which states, "Wanted, 1925 Paige fire truck, $25,000, if in mint condition," and Johnny says that it is exactly what the ad submitter wants. The "it" being Roy and Johnny's refurbished fire truck. The problem is that in 3x2, "The Old Engine," when Johnny and Roy are telling Chet and Marco about their purchase, Johnny says that it's a 1932 Dennis, and when they're looking it over, the blue "Dennis" emblem is attached to the hood of the engine.
Revealing mistake: After the MI patient from the construction site is brought to treatment 1, when Early uses the laryngoscope for an endotracheal intubation, we can see that he merely places the laryngoscope at the side of the man's face, especially since we can still see the entire distal end beside the man's neck.
Visible crew/equipment: While Brackett is on Copter 10, after the dispatcher tells the pilot that the truck driver has been heard on the CB saying that he's trapped in the cab, repeating the same location, when we see the bird's-eye view of Copter 10 flying below, the shadow of the filming chopper is right beside the shadow of Copter 10, at the top of the screen.