Continuity mistake: When Ritter pulls up to the overpass, the car's lights are on. They are off in the next shot when he exits the car and on again in the next shot as he walks away from it.
Escape Route - S9-E8
Continuity mistake: When Casey is in Molly's bar, Stella places a beer down in front of him. The level and amount of foam changes several times throughout the scene before Casey brings the glass to his lips.
Answer: Internet sources give many reasons why firefighters do this, but in regards to your question, it's probably because opening walls and ceilings creates better ventilation which allows heat and smoke to escape, giving firefighters better visibility and lowering the temperature.
raywest ★