Heavyweight - S3-E5
Continuity mistake: At the start, after Station 51 is dispatched to the apartment fire, when a musician asks Captain Stanley for help removing instruments from the burning building, the next shot showing Truck 98 rolling up is footage from 2x13, "Drivers", during the fire at the Atlas Hotel. We can even see the smoke through the Atlas Hotel's windows, and Squad 51 parked across the street. More footage from the Atlas Hotel fire is shown when Engine 16 rolls up. Additional footage from other episodes are shown as well, when we see helmets and rigs bearing company numbers that were not called to this fire.