When the firefighters break out the back window of the woman's van, it is obvious that it is annealed glass (probably sugar glass) rather than the laminated tempered glass required in vehicles.
When Squad 51 first gets on the freeway, the fog is supposed to be so thick that Johnny has to step out onto the running board for a better view, but in two shots from the vehicle perspective, a man is visible through the fog. He even casually walks off-camera in the second shot.
As the Station 51 crew starts out for the fog-bound freeway pileup, the first establishing shot of the station is in full, cloudless sunshine with blue sky. Then as the camera switches to a point-of-view from inside, it is an obvious use of a light gray "day-for-night" filter on the next several shots, before they get to the actual on-set fog effects.
While responding to the accident, Gage tells the accident victim who was pleading him to help his brother to close the hood on a wrecked car to smother a fire. A short time later, the car hood is open again.
As the squad was driving through the fog, a crew member was visible standing on the on the right side of the scene when viewed through the windshield from Johnny's side. The person was standing the first two times he or she is seen. The third time you can see the person turn and walk out of the scene just before Johnny gets out of the squad.
The freeway pileup is said to be on the southbound 405, between Century Blvd. and Western Ave. When Captain Stanley asks Engine 45 to sound their horn to assess distance, he estimates Engine 45 "must be south of the curve" and "about a half-mile" from Engine 51. While there is a curve on the 405 Freeway between Century and Western, the distance is too great for Captain Stanley to have heard Engine 45's horn. The Century Blvd. offramp is near LAX (exit 46), and the Western offramp is in Torrance (Exit 38A), approximately eight miles apart from each other.
When Squad 51 is dispatched to the suicide attempt, the dispatcher says "time out, 1:32" which in conventional emergency dispatching would be 1:32 AM, since a 24-hour system is used. Since it is the early afternoon, he should have said "13:32".