Visible crew/equipment: When Station 51 arrive at the movie studio, after the car's explosion Captain Stanley tells dispatch to respond another engine, mobile aid unit, and another ambulance. In the next shot from the interior of Engine 51, the cameraman and camera are visible in the passenger side mirror.
Visible crew/equipment: When Station 51 is being dispatched to 'auto accident with injuries' there's a closeup of Sam Lanier, the dispatcher, and in the next overhead shot of the apparatus bay, we can see the reflection/shadow of equipment moving on Engine 51's windshield, at the bottom left corner.
Answer: It is standard practice to wet down driveways so that they stand out in a long shot.
stiiggy