When squad 51 returns from their first run, the fire engine in the garage is the Crown rig from the first few seasons, and not the Ward la France.
The first time Dr. Brackett talks to Tommy's mother, her purse strap switches from her shoulder to her arm between shots.
When Johnny and Roy are talking about the election in the station restroom, the lights above the sinks are on but the switches are in the Off position.
The sculptor (Sharon Gless) encases her male subject in plaster and glue, and doesn't call paramedics for a couple of hours. But plaster generates considerable heat as it dries, so the model would have been at risk for burns more than for itching, en-robed in that much plaster. This is why make-up artists do not use plaster on skin for life-casting.
Going up in the elevator the men are seen putting on their safety belts. But while climbing around on the crane they are never connected to a safety line, which would be 100% mandatory according to all safety rules.
When backing in to station after 1st run beacons on truck are not on. On closeup of vehicle entering station beacons are on.