Continuity mistake: When Dawson and the police detective are knocking the door of a suspect a neighbor is coming out to sidewalk and the snow is piled high along the sidewalk and parked cars. The next scene shows the ambulance and fire engine on the road with no trace of any snow. (00:44:00 - 00:47:00)
Continuity mistake: When Brett and Dawson go rescue the two climbers, at the very beginning you can see a long shot of the group where the victim is laying with her legs and arms straight, while in the rest of the scene she lies there haphazardly in consequence of the fall. (00:09:45)
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 ★