Deliberate mistake: After the fireworks begin exploding at the warehouse fire, when Captain Stanley and Roy are helping Willy out, they are knocked to the ground by an explosion, and in two of the following exterior shots the large sign that reads "Kiddytime Toy Co" is visible. This shot is from season 4, episode "The Screenwriter", when the guys respond to the fire at the toy factory that also made fireworks.
Continuity mistake: When Johnny is doing overtime with Engine 8, dispatch sends the two guys of Squad 8 on an unknown type rescue and they leave Station 8, but when Johnny and Captain Stone walk back into the kitchen, Squad 8 is still parked in the apparatus bay.
Visible crew/equipment: When Station 51 is dispatched to the injured sky diver, we can see the area around the electrical tower when they arrive, particularly where Roy and Johnny start climbing up. When Johnny rappels down with Lucky, in the wide shot, just as they reach the ground the crew's ladder can be seen at the right side of the screen, in the same area where Johnny and Roy started their climb.
Visible crew/equipment: When the dispatcher drops tones for the trapped victim of a traffic accident, just after we hear Captain Stanley say, "KMG365," we can see movement between the front passenger and driver seats of Engine 51, precisely where the camera is. Captain Stanley is still at the radio base station and Mike hasn't opened the door yet.
Continuity mistake: When Johnny and Roy are with the heart transplant patient who is having chest pains, after they contact Rampart, in the wide shots Johnny has the stethoscope around his neck, but in his closeups the stethoscope is gone.
Visible crew/equipment: When Gage and DeSoto are stuck cleaning the squad again before The Inspection, Captain Stanley walks in and the actor's T-mark is visible on the floor just before he steps on it. Additionally, when Stanley walks away, and Chet catches up to him, another T-mark is visible on the floor near the doorway.
Continuity mistake: Just before the opening credits both Engine 51 and Squad 51 are inside the station. The alarm goes off and when Squad 51 leaves the station Engine 51 has vanished.
Continuity mistake: During the actual rescue of the boy from the overturned car in the water, Roy's, Johnny's, and Chet's shoes are water-type shoes, which then change back to their uniform shoes.
Other mistake: When Squad 51 is dispatched to an 'unknown type rescue', as the squad rolls out we can see the Crown engine from the show's first two seasons parked in the apparatus bay, instead of 51's current Ward LaFrance.
Revealing mistake: When Station 51 responds to the traffic accident, after Captain Stanley hands Johnny the Ajax tool, in the closeup it's obvious that the hands are not really Johnny's. Then there's another shot of the real Johnny, but once he removes his goggles, interestingly it's the stunt double who's in the following shots by the car, even when Johnny cuts himself, it's the stunt double.
Continuity mistake: After Station 51 is dispatched to 'traffic accident, victim trapped', when they get the anti-shock suit on the boy Roy's watch reads 5:25. Then at the hospital, when Johnny asks Roy about the time, Roy looks at his watch and says "About 5:00."
Continuity mistake: During Roy and Johnny's rescue of the sky diver, the stuntmen are not wearing the fire department uniform shoes, they are wearing different shoes, and Roy's watch differs as well.
Continuity mistake: When Johnny walks into the office to drop off the trash bin, he sees the Chief's clock on the wall and it reads 2:09, but when Johnny brings the clock to Captain Stanley and he gives it to Chet to hide, the clock's hands read 6:44. And when they're all dispatched, the timeout is 14:15.
Continuity mistake: At the scene of the vehicle accident, when the boy is removed from the overturned car, he has a bruise near his chin that reaches below his mouth area. When he's in the ER, that bruise is now twice the size and reaches his cheek area.
Continuity mistake: When Roy and Johnny climb the electrical tower to rescue the sky diver, in the closeups Johnny hangs onto the diagonal cross beam when he reaches out to Lucky, but in the wide shot the stunt double hangs onto the tower's main vertical frame when he reaches out to Lucky.
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.
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.
Other mistake: After Chet's practical joke on Karen, she's quite ticked off, and Roy and Johnny are a bit uncomfortable, and then when Station 51 is dispatched to the unknown type rescue they all head to the apparatus bay. In the next shot when Karen, Roy, and Johnny get into the squad just watch all the actors' faces. First Johnny cracks up, then Roy and Karen, who even put their heads down to hide their laughter, particularly Roy who ducks his head behind the steering wheel. Fun to watch.
Visible crew/equipment: When Roy tells Karen that she'll know when she can do it on her own when she'll have to, the reflection of set lighting is visible on the squad's chrome spotlight. Additionally, when Station 51 is dispatched to the structure fire the rear bay door closed, but when the rigs roll out the rear bay door is open.
Other mistake: After Station 51 arrives at the structure fire, Captain Stanley tells Mike to get water to their lines (charging the two lines) and then mule the supply line back to the hydrant. When Marco and Chet get the two lines, they head to the house with Captain Stanley and start hosing the fire down with charged lines. A few shots later, we see Mike going to the back of Engine 51, and the two lines that Chet, Marco, and Cap have been using are flat and not even charged yet.
Answer: It is standard practice to wet down driveways so that they stand out in a long shot.
stiiggy