Other mistake: During the paint factory fire incident, when the Battalion Chief (Battalion 14) contacts LA dispatch over the HT he says, "LA, Battalion 14, this fire is contained," but the bizarre subtitles read "Calling Battalion 14..." Subtitles from Universal Studios 2010 DVD.
Other mistake: During the paint factory fire, when Engine 2 rolls up, we can see the red, large, rectangular vinyl material that is adhered to the front of the engine, with the company number printed on it. There's also vinyl material adhered to the top of the cab as well as the back of the engine with nothing on it, presumably covering the engine company's real number.
Other mistake: When Squad 51 is dispatched to the possible heart attack, while Chet’s at the base station responding to the dispatcher, the lightbar atop Squad 51 has nothing covering the chrome, but en route in the close up there's black tape covering much of the chrome trim.
Other mistake: During the fire at the paint factory, just after the barrels at the back of the pickup up truck explode, in the next shot we see Marco and Chet manning a hose. In this closeup, another fireman runs up to them and he's wearing a helmet with 51 on it, but it's obvious he's not one of 51's guys, plus Roy and John are with the burn victim and Mike's at the engine. The fact that it's a closeup and we can see perfectly well that he's not actually from 51 makes this too odd.
Other mistake: After Mr. Winthrop is brought to the ER, there is a closeup of his EKG monitor as it's picking up multiple PVCs, but when Brackett asks him about the tension in his life, the monitor seen behind him is showing a flat line. This happens once again after Roy and John leave the treatment room, just before they move him to CCU.
Answer: It is standard practice to wet down driveways so that they stand out in a long shot.
stiiggy