When Squad 39 arrives at the heart attack scene, the rig is similar to Squad 51 (probably the same rig with a different number on it), but at the fireworks factory, Squad 39 is an older model rig (possibly the original Squad 51 from the pilot).
The heart attack victim showed a flat line on the ECG. They then defibrillate two times. Defibrillation is only done when the patient is in V-fib, it would not be effective on a flat line.
Chet says the wall and door are warm but he feels them with heavy turnout gloves on both hands which would prevent him from determining the temperature.
After the construction worker is brought into Rampart by Squad 39, Dr. Early inserts a Laryngoscope for the Intubation Tube, however the scope can be seen resting on the side of the victims face and not inserted orally as it should have been to insert the tube.
Just after Johnny arrives at Station 8 for his overtime shift on Engine 8, Squad 8 is dispatched to an unknown type rescue. After the Squad departs the apparatus bay Code 3, Johnny goes back in the kitchen with the Captain. As they talk, the Squad can clearly be seen through the screen door parked in the bay as if it was never dispatched.
Johnny is working overtime at Station 8. Which would have equipment such as Helmets & Turnout coats. Since Johnny is working with Engine 8, you can see that he is wearing a Station 51 Paramedic helmet, which he wouldn't need at all.